From bbf28362487e0e5cc0690ac48561bd0d10f57c1b Mon Sep 17 00:00:00 2001 From: Amar Takhar Date: Sun, 17 Jan 2016 19:20:37 -0500 Subject: Rename old document for reference only. --- c_user/c_user_old_reference_only.rst | 23786 +++++++++++++++++++++++++++++++++ 1 file changed, 23786 insertions(+) create mode 100644 c_user/c_user_old_reference_only.rst (limited to 'c_user/c_user_old_reference_only.rst') diff --git a/c_user/c_user_old_reference_only.rst b/c_user/c_user_old_reference_only.rst new file mode 100644 index 0000000..fe2c2ad --- /dev/null +++ b/c_user/c_user_old_reference_only.rst @@ -0,0 +1,23786 @@ +:orphan: + + + +.. COMMENT: %**end of header + +.. COMMENT: COPYRIGHT (c) 1989-2013. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +.. COMMENT: Master file for the C User's Guide + +.. COMMENT: Joel's Questions + +.. COMMENT: 1. Why does paragraphindent only impact makeinfo? + +.. COMMENT: 2. Why does paragraphindent show up in HTML? + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +.. COMMENT: The following determines which set of the tables and figures we will use. + +.. COMMENT: We default to ASCII but if available TeX or HTML versions will + +.. COMMENT: be used instead. + +.. COMMENT: @clear use-html + +.. COMMENT: @clear use-tex + +.. COMMENT: The following variable says to use texinfo or html for the two column + +.. COMMENT: texinfo tables. For somethings the format does not look good in html. + +.. COMMENT: With our adjustment to the left column in TeX, it nearly always looks + +.. COMMENT: good printed. + +.. COMMENT: Custom whitespace adjustments. We could fiddle a bit more. + +.. COMMENT: @syncodeindex fn cp + +.. COMMENT: variable substitution info: + +.. COMMENT: the language is @value{LANGUAGE} + +.. COMMENT: NOTE: don't use underscore in the name + +.. COMMENT: Title Page Stuff + +.. COMMENT: I don't really like having a short title page. -joel + +.. COMMENT: @shorttitlepage RTEMS Applications C User's Guide + +==================== +RTEMS C User’s Guide +==================== + +.. COMMENT: COPYRIGHT (c) 1988-2015. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +.. COMMENT: The following puts a space somewhere on an otherwise empty page so we + +.. COMMENT: can force the copyright description onto a left hand page. + +COPYRIGHT © 1988 - 2015. + +On-Line Applications Research Corporation (OAR). + +The authors have used their best efforts in preparing +this material. These efforts include the development, research, +and testing of the theories and programs to determine their +effectiveness. No warranty of any kind, expressed or implied, +with regard to the software or the material contained in this +document is provided. No liability arising out of the +application or use of any product described in this document is +assumed. The authors reserve the right to revise this material +and to make changes from time to time in the content hereof +without obligation to notify anyone of such revision or changes. + +The RTEMS Project is hosted at http://www.rtems.org. Any +inquiries concerning RTEMS, its related support components, or its +documentation should be directed to the Community Project hosted athttp://www.rtems.org. + +Any inquiries for commercial services including training, support, custom +development, application development assistance should be directed tohttp://www.rtems.com. + +.. COMMENT: This prevents a black box from being printed on "overflow" lines. + +.. COMMENT: The alternative is to rework a sentence to avoid this problem. + +RTEMS Applications C User’s Guide +################################# + +List of Figures +############### + +.. COMMENT: COPYRIGHT (c) 1989-2015. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Preface +####### + +In recent years, the cost required to develop a +software product has increased significantly while the target +hardware costs have decreased. Now a larger portion of money is +expended in developing, using, and maintaining software. The +trend in computing costs is the complete dominance of software +over hardware costs. Because of this, it is necessary that +formal disciplines be established to increase the probability +that software is characterized by a high degree of correctness, +maintainability, and portability. In addition, these +disciplines must promote practices that aid in the consistent +and orderly development of a software system within schedule and +budgetary constraints. To be effective, these disciplines must +adopt standards which channel individual software efforts toward +a common goal. + +The push for standards in the software development +field has been met with various degrees of success. The +Microprocessor Operating Systems Interfaces (MOSI) effort has +experienced only limited success. As popular as the UNIX +operating system has grown, the attempt to develop a standard +interface definition to allow portable application development +has only recently begun to produce the results needed in this +area. Unfortunately, very little effort has been expended to +provide standards addressing the needs of the real-time +community. Several organizations have addressed this need +during recent years. + +The Real Time Executive Interface Definition (RTEID) +was developed by Motorola with technical input from Software +Components Group. RTEID was adopted by the VMEbus International +Trade Association (VITA) as a baseline draft for their proposed +standard multiprocessor, real-time executive interface, Open +Real-Time Kernel Interface Definition (ORKID). These two groups +are currently working together with the IEEE P1003.4 committee +to insure that the functionality of their proposed standards is +adopted as the real-time extensions to POSIX. + +This emerging standard defines an interface for the +development of real-time software to ease the writing of +real-time application programs that are directly portable across +multiple real-time executive implementations. This interface +includes both the source code interfaces and run-time behavior +as seen by a real-time application. It does not include the +details of how a kernel implements these functions. The +standard’s goal is to serve as a complete definition of external +interfaces so that application code that conforms to these +interfaces will execute properly in all real-time executive +environments. With the use of a standards compliant executive, +routines that acquire memory blocks, create and manage message +queues, establish and use semaphores, and send and receive +signals need not be redeveloped for a different real-time +environment as long as the new environment is compliant with the +standard. Software developers need only concentrate on the +hardware dependencies of the real-time system. Furthermore, +most hardware dependencies for real-time applications can be +localized to the device drivers. + +A compliant executive provides simple and flexible +real-time multiprocessing. It easily lends itself to both +tightly-coupled and loosely-coupled configurations (depending on +the system hardware configuration). Objects such as tasks, +queues, events, signals, semaphores, and memory blocks can be +designated as global objects and accessed by any task regardless +of which processor the object and the accessing task reside. + +The acceptance of a standard for real-time executives +will produce the same advantages enjoyed from the push for UNIX +standardization by AT&T’s System V Interface Definition and +IEEE’s POSIX efforts. A compliant multiprocessing executive +will allow close coupling between UNIX systems and real-time +executives to provide the many benefits of the UNIX development +environment to be applied to real-time software development. +Together they provide the necessary laboratory environment to +implement real-time, distributed, embedded systems using a wide +variety of computer architectures. + +A study was completed in 1988, within the Research, +Development, and Engineering Center, U.S. Army Missile Command, +which compared the various aspects of the Ada programming +language as they related to the application of Ada code in +distributed and/or multiple processing systems. Several +critical conclusions were derived from the study. These +conclusions have a major impact on the way the Army develops +application software for embedded applications. These impacts +apply to both in-house software development and contractor +developed software. + +A conclusion of the analysis, which has been +previously recognized by other agencies attempting to utilize +Ada in a distributed or multiprocessing environment, is that the +Ada programming language does not adequately support +multiprocessing. Ada does provide a mechanism for +multi-tasking, however, this capability exists only for a single +processor system. The language also does not have inherent +capabilities to access global named variables, flags or program +code. These critical features are essential in order for data +to be shared between processors. However, these drawbacks do +have workarounds which are sometimes awkward and defeat the +intent of software maintainability and portability goals. + +Another conclusion drawn from the analysis, was that +the run time executives being delivered with the Ada compilers +were too slow and inefficient to be used in modern missile +systems. A run time executive is the core part of the run time +system code, or operating system code, that controls task +scheduling, input/output management and memory management. +Traditionally, whenever efficient executive (also known as +kernel) code was required by the application, the user developed +in-house software. This software was usually written in +assembly language for optimization. + +Because of this shortcoming in the Ada programming +language, software developers in research and development and +contractors for project managed systems, are mandated by +technology to purchase and utilize off-the-shelf third party +kernel code. The contractor, and eventually the Government, +must pay a licensing fee for every copy of the kernel code used +in an embedded system. + +The main drawback to this development environment is +that the Government does not own, nor has the right to modify +code contained within the kernel. V&V techniques in this +situation are more difficult than if the complete source code +were available. Responsibility for system failures due to faulty +software is yet another area to be resolved under this +environment. + +The Guidance and Control Directorate began a software +development effort to address these problems. A project to +develop an experimental run time kernel was begun that will +eliminate the major drawbacks of the Ada programming language +mentioned above. The Real Time Executive for Multiprocessor Systems +(RTEMS) provides full capabilities for management of tasks, +interrupts, time, and multiple processors in addition to those +features typical of generic operating systems. The code is +Government owned, so no licensing fees are necessary. RTEMS has +been implemented in both the Ada and C programming languages. +It has been ported to the following processor families: + +- Altera NIOS II + +- Analog Devices Blackfin + +- Atmel AVR + +- ARM + +- Freescale (formerly Motorola) MC68xxx + +- Freescale (formerly Motorola) MC683xx + +- Freescale (formerly Motorola) ColdFire + +- Intel i386 and above + +- Lattice Semiconductor LM32 + +- NEC V850 + +- MIPS + +- PowerPC + +- Renesas (formerly Hitachi) SuperH + +- Renesas (formerly Hitachi) H8/300 + +- Renesas M32C + +- SPARC v7, v8, and V9 + +Support for other processor families, including RISC, CISC, and DSP, is +planned. Since almost all of RTEMS is written in a high level language, +ports to additional processor families require minimal effort. + +RTEMS multiprocessor support is capable of handling +either homogeneous or heterogeneous systems. The kernel +automatically compensates for architectural differences (byte +swapping, etc.) between processors. This allows a much easier +transition from one processor family to another without a major +system redesign. + +Since the proposed standards are still in draft form, +RTEMS cannot and does not claim compliance. However, the status +of the standard is being carefully monitored to guarantee that +RTEMS provides the functionality specified in the standard. +Once approved, RTEMS will be made compliant. + +This document is a detailed users guide for a +functionally compliant real-time multiprocessor executive. It +describes the user interface and run-time behavior of Release +4.10.99.0 of the C interface +to RTEMS. + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +.. COMMENT: This chapter is missing the following figures: + +.. COMMENT: Figure 1-1 RTEMS Application Architecture + +.. COMMENT: Figure 1-2 RTEMS Internal Architecture + +Overview +######## + +Introduction +============ + +RTEMS, Real-Time Executive for Multiprocessor Systems, is a +real-time executive (kernel) which provides a high performance +environment for embedded military applications including the +following features: + +- multitasking capabilities + +- homogeneous and heterogeneous multiprocessor systems + +- event-driven, priority-based, preemptive scheduling + +- optional rate monotonic scheduling + +- intertask communication and synchronization + +- priority inheritance + +- responsive interrupt management + +- dynamic memory allocation + +- high level of user configurability + +This manual describes the usage of RTEMS for +applications written in the C programming language. Those +implementation details that are processor dependent are provided +in the Applications Supplement documents. A supplement +document which addresses specific architectural issues that +affect RTEMS is provided for each processor type that is +supported. + +Real-time Application Systems +============================= + +Real-time application systems are a special class of +computer applications. They have a complex set of +characteristics that distinguish them from other software +problems. Generally, they must adhere to more rigorous +requirements. The correctness of the system depends not only on +the results of computations, but also on the time at which the +results are produced. The most important and complex +characteristic of real-time application systems is that they +must receive and respond to a set of external stimuli within +rigid and critical time constraints referred to as deadlines. +Systems can be buried by an avalanche of interdependent, +asynchronous or cyclical event streams. + +Deadlines can be further characterized as either hard +or soft based upon the value of the results when produced after +the deadline has passed. A deadline is hard if the results have +no value or if their use will result in a catastrophic event. +In contrast, results which are produced after a soft deadline +may have some value. + +Another distinguishing requirement of real-time +application systems is the ability to coordinate or manage a +large number of concurrent activities. Since software is a +synchronous entity, this presents special problems. One +instruction follows another in a repeating synchronous cycle. +Even though mechanisms have been developed to allow for the +processing of external asynchronous events, the software design +efforts required to process and manage these events and tasks +are growing more complicated. + +The design process is complicated further by +spreading this activity over a set of processors instead of a +single processor. The challenges associated with designing and +building real-time application systems become very complex when +multiple processors are involved. New requirements such as +interprocessor communication channels and global resources that +must be shared between competing processors are introduced. The +ramifications of multiple processors complicate each and every +characteristic of a real-time system. + +Real-time Executive +=================== + +Fortunately, real-time operating systems or real-time +executives serve as a cornerstone on which to build the +application system. A real-time multitasking executive allows +an application to be cast into a set of logical, autonomous +processes or tasks which become quite manageable. Each task is +internally synchronous, but different tasks execute +independently, resulting in an asynchronous processing stream. +Tasks can be dynamically paused for many reasons resulting in a +different task being allowed to execute for a period of time. +The executive also provides an interface to other system +components such as interrupt handlers and device drivers. +System components may request the executive to allocate and +coordinate resources, and to wait for and trigger synchronizing +conditions. The executive system calls effectively extend the +CPU instruction set to support efficient multitasking. By +causing tasks to travel through well-defined state transitions, +system calls permit an application to demand-switch between +tasks in response to real-time events. + +By proper grouping of responses to stimuli into +separate tasks, a system can now asynchronously switch between +independent streams of execution, directly responding to +external stimuli as they occur. This allows the system design +to meet critical performance specifications which are typically +measured by guaranteed response time and transaction throughput. +The multiprocessor extensions of RTEMS provide the features +necessary to manage the extra requirements introduced by a +system distributed across several processors. It removes the +physical barriers of processor boundaries from the world of the +system designer, enabling more critical aspects of the system to +receive the required attention. Such a system, based on an +efficient real-time, multiprocessor executive, is a more +realistic model of the outside world or environment for which it +is designed. As a result, the system will always be more +logical, efficient, and reliable. + +By using the directives provided by RTEMS, the +real-time applications developer is freed from the problem of +controlling and synchronizing multiple tasks and processors. In +addition, one need not develop, test, debug, and document +routines to manage memory, pass messages, or provide mutual +exclusion. The developer is then able to concentrate solely on +the application. By using standard software components, the +time and cost required to develop sophisticated real-time +applications is significantly reduced. + +RTEMS Application Architecture +============================== + +One important design goal of RTEMS was to provide a +bridge between two critical layers of typical real-time systems. +As shown in the following figure, RTEMS serves as a buffer between the +project dependent application code and the target hardware. +Most hardware dependencies for real-time applications can be +localized to the low level device drivers. + +.. code:: c + + +-----------------------------------------------------------+ + | Application Dependent Software | + | +----------------------------------------+ | + | | Standard Application Components | | + | | +-------------+---+ | + | +---+-----------+ | | | + | | Board Support | | RTEMS | | + | | Package | | | | + +----+---------------+--------------+-----------------+-----| + | Target Hardware | + +-----------------------------------------------------------+ + +The RTEMS I/O interface manager provides an efficient tool for incorporating +these hardware dependencies into the system while simultaneously +providing a general mechanism to the application code that +accesses them. A well designed real-time system can benefit +from this architecture by building a rich library of standard +application components which can be used repeatedly in other +real-time projects. + +RTEMS Internal Architecture +=========================== + +RTEMS can be viewed as a set of layered components that work in +harmony to provide a set of services to a real-time application +system. The executive interface presented to the application is +formed by grouping directives into logical sets called resource managers. +Functions utilized by multiple managers such as scheduling, +dispatching, and object management are provided in the executive +core. The executive core depends on a small set of CPU dependent routines. +Together these components provide a powerful run time +environment that promotes the development of efficient real-time +application systems. The following figure illustrates this organization: + +.. code:: c + + +-----------------------------------------------+ + | RTEMS Executive Interface | + +-----------------------------------------------+ + | RTEMS Core | + +-----------------------------------------------+ + | CPU Dependent Code | + +-----------------------------------------------+ + +Subsequent chapters present a detailed description of the capabilities +provided by each of the following RTEMS managers: + +- initialization + +- task + +- interrupt + +- clock + +- timer + +- semaphore + +- message + +- event + +- signal + +- partition + +- region + +- dual ported memory + +- I/O + +- fatal error + +- rate monotonic + +- user extensions + +- multiprocessing + +User Customization and Extensibility +==================================== + +As thirty-two bit microprocessors have decreased in +cost, they have become increasingly common in a variety of +embedded systems. A wide range of custom and general-purpose +processor boards are based on various thirty-two bit processors. +RTEMS was designed to make no assumptions concerning the +characteristics of individual microprocessor families or of +specific support hardware. In addition, RTEMS allows the system +developer a high degree of freedom in customizing and extending +its features. + +RTEMS assumes the existence of a supported +microprocessor and sufficient memory for both RTEMS and the +real-time application. Board dependent components such as +clocks, interrupt controllers, or I/O devices can be easily +integrated with RTEMS. The customization and extensibility +features allow RTEMS to efficiently support as many environments +as possible. + +Portability +=========== + +The issue of portability was the major factor in the +creation of RTEMS. Since RTEMS is designed to isolate the +hardware dependencies in the specific board support packages, +the real-time application should be easily ported to any other +processor. The use of RTEMS allows the development of real-time +applications which can be completely independent of a particular +microprocessor architecture. + +Memory Requirements +=================== + +Since memory is a critical resource in many real-time +embedded systems, RTEMS was specifically designed to automatically +leave out all services that are not required from the run-time +environment. Features such as networking, various fileystems, +and many other features are completely optional. This allows +the application designer the flexibility to tailor RTEMS to most +efficiently meet system requirements while still satisfying even +the most stringent memory constraints. As a result, the size +of the RTEMS executive is application dependent. + +RTEMS requires RAM to manage each instance of an RTEMS object +that is created. Thus the more RTEMS objects an application +needs, the more memory that must be reserved. See `Configuring a System`_. + +RTEMS utilizes memory for both code and data space. +Although RTEMS’ data space must be in RAM, its code space can be +located in either ROM or RAM. + +Audience +======== + +This manual was written for experienced real-time +software developers. Although some background is provided, it +is assumed that the reader is familiar with the concepts of task +management as well as intertask communication and +synchronization. Since directives, user related data +structures, and examples are presented in C, a basic +understanding of the C programming language +is required to fully +understand the material presented. However, because of the +similarity of the Ada and C RTEMS implementations, users will +find that the use and behavior of the two implementations is +very similar. A working knowledge of the target processor is +helpful in understanding some of RTEMS’ features. A thorough +understanding of the executive cannot be obtained without +studying the entire manual because many of RTEMS’ concepts and +features are interrelated. Experienced RTEMS users will find +that the manual organization facilitates its use as a reference +document. + +Conventions +=========== + +The following conventions are used in this manual: + +- Significant words or phrases as well as all directive + names are printed in bold type. + +- Items in bold capital letters are constants defined by + RTEMS. Each language interface provided by RTEMS includes a + file containing the standard set of constants, data types, and + structure definitions which can be incorporated into the user + application. + +- A number of type definitions are provided by RTEMS and + can be found in rtems.h. + +- The characters "0x" preceding a number indicates that + the number is in hexadecimal format. Any other numbers are + assumed to be in decimal format. + +Manual Organization +=================== + +This first chapter has presented the introductory and +background material for the RTEMS executive. The remaining +chapters of this manual present a detailed description of RTEMS +and the environment, including run time behavior, it creates for +the user. + +A chapter is dedicated to each manager and provides a +detailed discussion of each RTEMS manager and the directives +which it provides. The presentation format for each directive +includes the following sections: + +- Calling sequence + +- Directive status codes + +- Description + +- Notes + +The following provides an overview of the remainder +of this manual: + +Chapter 2: + Key Concepts: presents an introduction to the ideas which are common + across multiple RTEMS managers. + +Chapter 3: + RTEMS Data Types: describes the fundamental data types shared + by the services in the RTEMS Classic API. + +Chapter 4: + Scheduling Concepts: details the various RTEMS scheduling algorithms + and task state transitions. + +Chapter 5: + Initialization Manager: describes the functionality and directives + provided by the Initialization Manager. + +Chapter 6: + Task Manager: describes the functionality and directives provided + by the Task Manager. + +Chapter 7: + Interrupt Manager: describes the functionality and directives + provided by the Interrupt Manager. + +Chapter 8: + Clock Manager: describes the functionality and directives + provided by the Clock Manager. + +Chapter 9: + Timer Manager: describes the functionality and directives provided + by the Timer Manager. + +Chapter 10: + Rate Monotonic Manager: describes the functionality and directives + provided by the Rate Monotonic Manager. + +Chapter 11: + Semaphore Manager: describes the functionality and directives + provided by the Semaphore Manager. + +Chapter 12: + Barrier Manager: describes the functionality and directives + provided by the Barrier Manager. + +Chapter 13: + Message Manager: describes the functionality and directives + provided by the Message Manager. + +Chapter 14: + Event Manager: describes the + functionality and directives provided by the Event Manager. + +Chapter 15: + Signal Manager: describes the + functionality and directives provided by the Signal Manager. + +Chapter 16: + Partition Manager: describes the + functionality and directives provided by the Partition Manager. + +Chapter 17: + Region Manager: describes the + functionality and directives provided by the Region Manager. + +Chapter 18: + Dual-Ported Memory Manager: describes + the functionality and directives provided by the Dual-Ported + Memory Manager. + +Chapter 19: + I/O Manager: describes the + functionality and directives provided by the I/O Manager. + +Chapter 20: + Fatal Error Manager: describes the functionality and directives + provided by the Fatal Error Manager. + +Chapter 21: + Board Support Packages: defines the + functionality required of user-supplied board support packages. + +Chapter 22: + User Extensions: shows the user how to + extend RTEMS to incorporate custom features. + +Chapter 23: + Configuring a System: details the process by which one tailors RTEMS + for a particular single-processor or multiprocessor application. + +Chapter 24: + Multiprocessing Manager: presents a + conceptual overview of the multiprocessing capabilities provided + by RTEMS as well as describing the Multiprocessing + Communications Interface Layer and Multiprocessing Manager + directives. + +Chapter 25: + Stack Bounds Checker: presents the capabilities of the RTEMS + task stack checker which can report stack usage as well as detect + bounds violations. + +Chapter 26: + CPU Usage Statistics: presents the capabilities of the CPU Usage + statistics gathered on a per task basis along with the mechanisms + for reporting and resetting the statistics. + +Chapter 27: + Object Services: presents a collection of helper services useful + when manipulating RTEMS objects. These include methods to assist + in obtaining an object’s name in printable form. Additional services + are provided to decompose an object Id and determine which API + and object class it belongs to. + +Chapter 28: + Chains: presents the methods provided to build, iterate and + manipulate doubly-linked chains. This manager makes the + chain implementation used internally by RTEMS to user space + applications. + +Chapter 29: + Timespec Helpers: presents a set of helper services useful + when manipulating POSIX ``struct timespec`` instances. + +Chapter 30: + Constant Bandwidth Server Scheduler API. + +Chapter 31: + Directive Status Codes: provides a definition of each of the + directive status codes referenced in this manual. + +Chapter 32: + Example Application: provides a template for simple RTEMS applications. + +Chapter 33: + Glossary: defines terms used throughout this manual. + +.. COMMENT: COPYRIGHT (c) 1988-2007. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +.. COMMENT: The following figure was replaced with an ASCII equivalent. + +.. COMMENT: Figure 2-1 Object ID Composition + +Key Concepts +############ + +Introduction +============ + +The facilities provided by RTEMS are built upon a +foundation of very powerful concepts. These concepts must be +understood before the application developer can efficiently +utilize RTEMS. The purpose of this chapter is to familiarize +one with these concepts. + +Objects +======= + +.. index:: objects + +RTEMS provides directives which can be used to +dynamically create, delete, and manipulate a set of predefined +object types. These types include tasks, message queues, +semaphores, memory regions, memory partitions, timers, ports, +and rate monotonic periods. The object-oriented nature of RTEMS +encourages the creation of modular applications built upon +re-usable "building block" routines. + +All objects are created on the local node as required +by the application and have an RTEMS assigned ID. All objects +have a user-assigned name. Although a relationship exists +between an object’s name and its RTEMS assigned ID, the name and +ID are not identical. Object names are completely arbitrary and +selected by the user as a meaningful "tag" which may commonly +reflect the object’s use in the application. Conversely, object +IDs are designed to facilitate efficient object manipulation by +the executive. + +Object Names +------------ +.. index:: object name +.. index:: rtems_object_name + +An object name is an unsigned thirty-two bit entity +associated with the object by the user. The data type``rtems_name`` is used to store object names... index:: rtems_build_name + +Although not required by RTEMS, object names are often +composed of four ASCII characters which help identify that object. +For example, a task which causes a light to blink might be +called "LITE". The ``rtems_build_name`` routine +is provided to build an object name from four ASCII characters. +The following example illustrates this: +.. code:: c + + rtems_object_name my_name; + my_name = rtems_build_name( 'L', 'I', 'T', 'E' ); + +However, it is not required that the application use ASCII +characters to build object names. For example, if an +application requires one-hundred tasks, it would be difficult to +assign meaningful ASCII names to each task. A more convenient +approach would be to name them the binary values one through +one-hundred, respectively... index:: rtems_object_get_name + +RTEMS provides a helper routine, ``rtems_object_get_name``, +which can be used to obtain the name of any RTEMS object using just +its ID. This routine attempts to convert the name into a printable string. + +The following example illustrates the use of this method to print +an object name: +.. code:: c + + #include + #include + void print_name(rtems_id id) + { + char buffer[10]; /* name assumed to be 10 characters or less \*/ + char \*result; + result = rtems_object_get_name( id, sizeof(buffer), buffer ); + printk( "ID=0x%08x name=%s\\n", id, ((result) ? result : "no name") ); + } + +Object IDs +---------- + +.. index:: object ID +.. index:: object ID composition +.. index:: rtems_id + +An object ID is a unique unsigned integer value which uniquely identifies +an object instance. Object IDs are passed as arguments to many directives +in RTEMS and RTEMS translates the ID to an internal object pointer. The +efficient manipulation of object IDs is critical to the performance +of RTEMS services. Because of this, there are two object Id formats +defined. Each target architecture specifies which format it will use. +There is a thirty-two bit format which is used for most of the supported +architectures and supports multiprocessor configurations. There is also +a simpler sixteen bit format which is appropriate for smaller target +architectures and does not support multiprocessor configurations. + +Thirty-Two Object ID Format +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The thirty-two bit format for an object ID is composed of four parts: API, +object class, node, and index. The data type ``rtems_id`` +is used to store object IDs. + +.. code:: c + + 31 27 26 24 23 16 15 0 + +---------+-------+--------------+-------------------------------+ + | | | | | + | Class | API | Node | Index | + | | | | | + +---------+-------+--------------+-------------------------------+ + +The most significant five bits are the object class. The next +three bits indicate the API to which the object class belongs. +The next eight bits (16-23) are the number of the node on which +this object was created. The node number is always one (1) in a single +processor system. The least significant sixteen bits form an +identifier within a particular object type. This identifier, +called the object index, ranges in value from 1 to the maximum +number of objects configured for this object type. + +Sixteen Bit Object ID Format +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The sixteen bit format for an object ID is composed of three parts: API, +object class, and index. The data type ``rtems_id`` +is used to store object IDs. + +.. code:: c + + 15 11 10 8 7 0 + +---------+-------+--------------+ + | | | | + | Class | API | Index | + | | | | + +---------+-------+--------------+ + +The sixteen-bit format is designed to be as similar as possible to the +thrity-two bit format. The differences are limited to the eliminatation +of the node field and reduction of the index field from sixteen-bits +to 8-bits. Thus the sixteen bit format only supports up to 255 object +instances per API/Class combination and single processor systems. +As this format is typically utilized by sixteen-bit processors with +limited address space, this is more than enough object instances. + +Object ID Description +--------------------- + +The components of an object ID make it possible +to quickly locate any object in even the most complicated +multiprocessor system. Object ID’s are associated with an +object by RTEMS when the object is created and the corresponding +ID is returned by the appropriate object create directive. The +object ID is required as input to all directives involving +objects, except those which create an object or obtain the ID of +an object. + +The object identification directives can be used to +dynamically obtain a particular object’s ID given its name. +This mapping is accomplished by searching the name table +associated with this object type. If the name is non-unique, +then the ID associated with the first occurrence of the name +will be returned to the application. Since object IDs are +returned when the object is created, the object identification +directives are not necessary in a properly designed single +processor application. + +In addition, services are provided to portably examine the +subcomponents of an RTEMS ID. These services are +described in detail later in this manual but are prototyped +as follows:.. index:: obtaining class from object ID +.. index:: obtaining node from object ID +.. index:: obtaining index from object ID +.. index:: get class from object ID +.. index:: get node from object ID +.. index:: get index from object ID +.. index:: rtems_object_id_get_api +.. index:: rtems_object_id_get_class +.. index:: rtems_object_id_get_node +.. index:: rtems_object_id_get_index + +.. code:: c + + uint32_t rtems_object_id_get_api( rtems_id ); + uint32_t rtems_object_id_get_class( rtems_id ); + uint32_t rtems_object_id_get_node( rtems_id ); + uint32_t rtems_object_id_get_index( rtems_id ); + +An object control block is a data structure defined +by RTEMS which contains the information necessary to manage a +particular object type. For efficiency reasons, the format of +each object type’s control block is different. However, many of +the fields are similar in function. The number of each type of +control block is application dependent and determined by the +values specified in the user’s Configuration Table. An object +control block is allocated at object create time and freed when +the object is deleted. With the exception of user extension +routines, object control blocks are not directly manipulated by +user applications. + +Communication and Synchronization +================================= +.. index:: communication and synchronization + +In real-time multitasking applications, the ability +for cooperating execution threads to communicate and synchronize +with each other is imperative. A real-time executive should +provide an application with the following capabilities: + +- Data transfer between cooperating tasks + +- Data transfer between tasks and ISRs + +- Synchronization of cooperating tasks + +- Synchronization of tasks and ISRs + +Most RTEMS managers can be used to provide some form +of communication and/or synchronization. However, managers +dedicated specifically to communication and synchronization +provide well established mechanisms which directly map to the +application’s varying needs. This level of flexibility allows +the application designer to match the features of a particular +manager with the complexity of communication and synchronization +required. The following managers were specifically designed for +communication and synchronization: + +- Semaphore + +- Message Queue + +- Event + +- Signal + +The semaphore manager supports mutual exclusion +involving the synchronization of access to one or more shared +user resources. Binary semaphores may utilize the optional +priority inheritance algorithm to avoid the problem of priority +inversion. The message manager supports both communication and +synchronization, while the event manager primarily provides a +high performance synchronization mechanism. The signal manager +supports only asynchronous communication and is typically used +for exception handling. + +Time +==== +.. index:: time + +The development of responsive real-time applications +requires an understanding of how RTEMS maintains and supports +time-related operations. The basic unit of time in RTEMS is +known as a tick. The frequency of clock ticks is completely +application dependent and determines the granularity and +accuracy of all interval and calendar time operations... index:: rtems_interval + +By tracking time in units of ticks, RTEMS is capable +of supporting interval timing functions such as task delays, +timeouts, timeslicing, the delayed execution of timer service +routines, and the rate monotonic scheduling of tasks. An +interval is defined as a number of ticks relative to the current +time. For example, when a task delays for an interval of ten +ticks, it is implied that the task will not execute until ten +clock ticks have occurred. +All intervals are specified using data type``rtems_interval``. + +A characteristic of interval timing is that the +actual interval period may be a fraction of a tick less than the +interval requested. This occurs because the time at which the +delay timer is set up occurs at some time between two clock +ticks. Therefore, the first countdown tick occurs in less than +the complete time interval for a tick. This can be a problem if +the clock granularity is large. + +The rate monotonic scheduling algorithm is a hard +real-time scheduling methodology. This methodology provides +rules which allows one to guarantee that a set of independent +periodic tasks will always meet their deadlines – even under +transient overload conditions. The rate monotonic manager +provides directives built upon the Clock Manager’s interval +timer support routines. + +Interval timing is not sufficient for the many +applications which require that time be kept in wall time or +true calendar form. Consequently, RTEMS maintains the current +date and time. This allows selected time operations to be +scheduled at an actual calendar date and time. For example, a +task could request to delay until midnight on New Year’s Eve +before lowering the ball at Times Square. +The data type ``rtems_time_of_day`` is used to specify +calendar time in RTEMS services. +See `Time and Date Data Structures`_ + +... index:: rtems_time_of_day + +Obviously, the directives which use intervals or wall +time cannot operate without some external mechanism which +provides a periodic clock tick. This clock tick is typically +provided by a real time clock or counter/timer device. + +Memory Management +================= +.. index:: memory management + +RTEMS memory management facilities can be grouped +into two classes: dynamic memory allocation and address +translation. Dynamic memory allocation is required by +applications whose memory requirements vary through the +application’s course of execution. Address translation is +needed by applications which share memory with another CPU or an +intelligent Input/Output processor. The following RTEMS +managers provide facilities to manage memory: + +- Region + +- Partition + +- Dual Ported Memory + +RTEMS memory management features allow an application +to create simple memory pools of fixed size buffers and/or more +complex memory pools of variable size segments. The partition +manager provides directives to manage and maintain pools of +fixed size entities such as resource control blocks. +Alternatively, the region manager provides a more general +purpose memory allocation scheme that supports variable size +blocks of memory which are dynamically obtained and freed by the +application. The dual-ported memory manager provides executive +support for address translation between internal and external +dual-ported RAM address space. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +RTEMS Data Types +################ + +Introduction +============ + +This chapter contains a complete list of the RTEMS primitive +data types in alphabetical order. This is intended to be +an overview and the user is encouraged to look at the appropriate +chapters in the manual for more information about the +usage of the various data types. + +List of Data Types +================== + +The following is a complete list of the RTEMS primitive +data types in alphabetical order: + +- .. index:: rtems_address + + ``rtems_address`` is the data type used to manage + addresses. It is equivalent to + a "void \*" pointer. + +- .. index:: rtems_asr + + ``rtems_asr`` is the return type for an + RTEMS ASR. + +- .. index:: rtems_asr_entry + + ``rtems_asr_entry`` is the address of + the entry point to an RTEMS ASR. + +- .. index:: rtems_attribute + + ``rtems_attribute`` is the data type used + to manage the attributes for RTEMS objects. It is primarily + used as an argument to object create routines to specify + characteristics of the new object. + +- .. index:: rtems_boolean + + ``rtems_boolean`` may only take on the + values of ``TRUE`` and ``FALSE``. + This type is deprecated. Use "bool" instead. + +- .. index:: rtems_context + + ``rtems_context`` is the CPU dependent + data structure used to manage the integer and system + register portion of each task’s context. + +- .. index:: rtems_context_fp + + ``rtems_context_fp`` is the CPU dependent + data structure used to manage the floating point portion of + each task’s context. + +- .. index:: rtems_device_driver + + ``rtems_device_driver`` is the + return type for a RTEMS device driver routine. + +- .. index:: rtems_device_driver_entry + + ``rtems_device_driver_entry`` is the + entry point to a RTEMS device driver routine. + +- .. index:: rtems_device_major_number + + ``rtems_device_major_number`` is the + data type used to manage device major numbers. + +- .. index:: rtems_device_minor_number + + ``rtems_device_minor_number`` is the + data type used to manage device minor numbers. + +- .. index:: rtems_double + + ``rtems_double`` is the RTEMS data + type that corresponds to double precision floating point + on the target hardware. + This type is deprecated. Use "double" instead. + +- .. index:: rtems_event_set + + ``rtems_event_set`` is the data + type used to manage and manipulate RTEMS event sets + with the Event Manager. + +- .. index:: rtems_extension + + ``rtems_extension`` is the return type + for RTEMS user extension routines. + +- .. index:: rtems_fatal_extension + + ``rtems_fatal_extension`` is the + entry point for a fatal error user extension handler routine. + +- .. index:: rtems_id + + ``rtems_id`` is the data type used + to manage and manipulate RTEMS object IDs. + +- .. index:: rtems_interrupt_frame + + ``rtems_interrupt_frame`` is the + data structure that defines the format of the interrupt + stack frame as it appears to a user ISR. This data + structure may not be defined on all ports. + +- .. index:: rtems_interrupt_level + + ``rtems_interrupt_level`` is the + data structure used with the ``rtems_interrupt_disable``,``rtems_interrupt_enable``, and``rtems_interrupt_flash`` routines. This + data type is CPU dependent and usually corresponds to + the contents of the processor register containing + the interrupt mask level. + +- .. index:: rtems_interval + + ``rtems_interval`` is the data + type used to manage and manipulate time intervals. + Intervals are non-negative integers used to measure + the length of time in clock ticks. + +- .. index:: rtems_isr + + ``rtems_isr`` is the return type + of a function implementing an RTEMS ISR. + +- .. index:: rtems_isr_entry + + ``rtems_isr_entry`` is the address of + the entry point to an RTEMS ISR. It is equivalent to the + entry point of the function implementing the ISR. + +- .. index:: rtems_mp_packet_classes + + ``rtems_mp_packet_classes`` is the + enumerated type which specifies the categories of + multiprocessing messages. For example, one of the + classes is for messages that must be processed by + the Task Manager. + +- .. index:: rtems_mode + + ``rtems_mode`` is the data type + used to manage and dynamically manipulate the execution + mode of an RTEMS task. + +- .. index:: rtems_mpci_entry + + ``rtems_mpci_entry`` is the return type + of an RTEMS MPCI routine. + +- .. index:: rtems_mpci_get_packet_entry + + ``rtems_mpci_get_packet_entry`` is the address of + the entry point to the get packet routine for an MPCI implementation. + +- .. index:: rtems_mpci_initialization_entry + + ``rtems_mpci_initialization_entry`` is the address of + the entry point to the initialization routine for an MPCI implementation. + +- .. index:: rtems_mpci_receive_packet_entry + + ``rtems_mpci_receive_packet_entry`` is the address of + the entry point to the receive packet routine for an MPCI implementation. + +- .. index:: rtems_mpci_return_packet_entry + + ``rtems_mpci_return_packet_entry`` is the address of + the entry point to the return packet routine for an MPCI implementation. + +- .. index:: rtems_mpci_send_packet_entry + + ``rtems_mpci_send_packet_entry`` is the address of + the entry point to the send packet routine for an MPCI implementation. + +- .. index:: rtems_mpci_table + + ``rtems_mpci_table`` is the data structure + containing the configuration information for an MPCI. + +- .. index:: rtems_name + + ``rtems_name`` is the data type used to + contain the name of a Classic API object. It is an unsigned + thirty-two bit integer which can be treated as a numeric + value or initialized using ``rtems_build_name`` to + contain four ASCII characters. + +- .. index:: rtems_option + + ``rtems_option`` is the data type + used to specify which behavioral options the caller desires. + It is commonly used with potentially blocking directives to specify + whether the caller is willing to block or return immediately with an error + indicating that the resource was not available. + +- .. index:: rtems_packet_prefix + + ``rtems_packet_prefix`` is the data structure + that defines the first bytes in every packet sent between nodes + in an RTEMS multiprocessor system. It contains routing information + that is expected to be used by the MPCI layer. + +- .. index:: rtems_signal_set + + ``rtems_signal_set`` is the data + type used to manage and manipulate RTEMS signal sets + with the Signal Manager. + +- .. index:: int8_t + + ``int8_t`` is the C99 data type that corresponds to signed eight + bit integers. This data type is defined by RTEMS in a manner that + ensures it is portable across different target processors. + +- .. index:: int16_t + + ``int16_t`` is the C99 data type that corresponds to signed + sixteen bit integers. This data type is defined by RTEMS in a manner + that ensures it is portable across different target processors. + +- .. index:: int32_t + + ``int32_t`` is the C99 data type that corresponds to signed + thirty-two bit integers. This data type is defined by RTEMS in a manner + that ensures it is portable across different target processors. + +- .. index:: int64_t + + ``int64_t`` is the C99 data type that corresponds to signed + sixty-four bit integers. This data type is defined by RTEMS in a manner + that ensures it is portable across different target processors. + +- .. index:: rtems_single + + ``rtems_single`` is the RTEMS data + type that corresponds to single precision floating point + on the target hardware. + This type is deprecated. Use "float" instead. + +- .. index:: rtems_status_codes + + ``rtems_status_codes`` is the return type for most + RTEMS services. This is an enumerated type of approximately twenty-five + values. In general, when a service returns a particular status code, it + indicates that a very specific error condition has occurred. + +- .. index:: rtems_task + + ``rtems_task`` is the return type for an + RTEMS Task. + +- .. index:: rtems_task_argument + + ``rtems_task_argument`` is the data + type for the argument passed to each RTEMS task. In RTEMS 4.7 + and older, this is an unsigned thirty-two bit integer. In + RTEMS 4.8 and newer, this is based upon the C99 type ``uintptr_t`` + which is guaranteed to be an integer large enough to hold a + pointer on the target architecture. + +- .. index:: rtems_task_begin_extension + + ``rtems_task_begin_extension`` is the + entry point for a task beginning execution user extension handler routine. + +- .. index:: rtems_task_create_extension + + ``rtems_task_create_extension`` is the + entry point for a task creation execution user extension handler routine. + +- .. index:: rtems_task_delete_extension + + ``rtems_task_delete_extension`` is the + entry point for a task deletion user extension handler routine. + +- .. index:: rtems_task_entry + + ``rtems_task_entry`` is the address of + the entry point to an RTEMS ASR. It is equivalent to the + entry point of the function implementing the ASR. + +- .. index:: rtems_task_exitted_extension + + ``rtems_task_exitted_extension`` is the + entry point for a task exitted user extension handler routine. + +- .. index:: rtems_task_priority + + ``rtems_task_priority`` is the data type + used to manage and manipulate task priorities. + +- .. index:: rtems_task_restart_extension + + ``rtems_task_restart_extension`` is the + entry point for a task restart user extension handler routine. + +- .. index:: rtems_task_start_extension + + ``rtems_task_start_extension`` is the + entry point for a task start user extension handler routine. + +- .. index:: rtems_task_switch_extension + + ``rtems_task_switch_extension`` is the + entry point for a task context switch user extension handler routine. + +- .. index:: rtems_tcb + + ``rtems_tcb`` is the data structure associated + with each task in an RTEMS system. + +- .. index:: rtems_time_of_day + + ``rtems_time_of_day`` is the data structure + used to manage and manipulate calendar time in RTEMS. + +- .. index:: rtems_timer_service_routine + + ``rtems_timer_service_routine`` is the + return type for an RTEMS Timer Service Routine. + +- .. index:: rtems_timer_service_routine_entry + + ``rtems_timer_service_routine_entry`` is the address of + the entry point to an RTEMS TSR. It is equivalent to the + entry point of the function implementing the TSR. + +- .. index:: rtems_vector_number + + ``rtems_vector_number`` is the data + type used to manage and manipulate interrupt vector numbers. + +- .. index:: uint8_t + + ``uint8_t`` is the C99 data type that corresponds to unsigned + eight bit integers. This data type is defined by RTEMS in a manner that + ensures it is portable across different target processors. + +- .. index:: uint16_t + + ``uint16_t`` is the C99 data type that corresponds to unsigned + sixteen bit integers. This data type is defined by RTEMS in a manner + that ensures it is portable across different target processors. + +- .. index:: uint32_t + + ``uint32_t`` is the C99 data type that corresponds to unsigned + thirty-two bit integers. This data type is defined by RTEMS in a manner + that ensures it is portable across different target processors. + +- .. index:: uint64_t + + ``uint64_t`` is the C99 data type that corresponds to unsigned + sixty-four bit integers. This data type is defined by RTEMS in a manner + that ensures it is portable across different target processors. + +- .. index:: uintptr_t + + ``uintptr_t`` is the C99 data type that corresponds to the + unsigned integer type that is of sufficient size to represent addresses + as unsigned integers. This data type is defined by RTEMS in a manner + that ensures it is portable across different target processors. + +.. COMMENT: COPYRIGHT (c) 1988-2011. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Scheduling Concepts +################### + +.. index:: scheduling +.. index:: task scheduling + +Introduction +============ + +The concept of scheduling in real-time systems dictates the ability to +provide immediate response to specific external events, particularly +the necessity of scheduling tasks to run within a specified time limit +after the occurrence of an event. For example, software embedded in +life-support systems used to monitor hospital patients must take instant +action if a change in the patient’s status is detected. + +The component of RTEMS responsible for providing this capability is +appropriately called the scheduler. The scheduler’s sole purpose is +to allocate the all important resource of processor time to the various +tasks competing for attention. + +Scheduling Algorithms +===================== + +.. index:: scheduling algorithms + +RTEMS provides a plugin framework which allows it to support +multiple scheduling algorithms. RTEMS now includes multiple +scheduling algorithms in the SuperCore and the user can select which +of these they wish to use in their application. In addition, +the user can implement their own scheduling algorithm and +configure RTEMS to use it. + +Supporting multiple scheduling algorithms gives the end user the +option to select the algorithm which is most appropriate to their use +case. Most real-time operating systems schedule tasks using a priority +based algorithm, possibly with preemption control. The classic +RTEMS scheduling algorithm which was the only algorithm available +in RTEMS 4.10 and earlier, is a priority based scheduling algorithm. +This scheduling algoritm is suitable for single core (e.g. non-SMP) +systems and is now known as the *Deterministic Priority Scheduler*. +Unless the user configures another scheduling algorithm, RTEMS will use +this on single core systems. + +Priority Scheduling +------------------- +.. index:: priority scheduling + +When using priority based scheduling, RTEMS allocates the processor using +a priority-based, preemptive algorithm augmented to provide round-robin +characteristics within individual priority groups. The goal of this +algorithm is to guarantee that the task which is executing on the +processor at any point in time is the one with the highest priority +among all tasks in the ready state. + +When a task is added to the ready chain, it is placed behind all other +tasks of the same priority. This rule provides a round-robin within +priority group scheduling characteristic. This means that in a group of +equal priority tasks, tasks will execute in the order they become ready +or FIFO order. Even though there are ways to manipulate and adjust task +priorities, the most important rule to remember is: + +- *Priority based scheduling algorithms will always select the + highest priority task that is ready to run when allocating the processor + to a task.* + +Priority scheduling is the most commonly used scheduling algorithm. +It should be used by applications in which multiple tasks contend for +CPU time or other resources and there is a need to ensure certain tasks +are given priority over other tasks. + +There are a few common methods of accomplishing the mechanics of this +algorithm. These ways involve a list or chain of tasks in the ready state. + +- The least efficient method is to randomly place tasks in the ready + chain forcing the scheduler to scan the entire chain to determine which + task receives the processor. + +- A more efficient method is to schedule the task by placing it + in the proper place on the ready chain based on the designated scheduling + criteria at the time it enters the ready state. Thus, when the processor + is free, the first task on the ready chain is allocated the processor. + +- Another mechanism is to maintain a list of FIFOs per priority. + When a task is readied, it is placed on the rear of the FIFO for its + priority. This method is often used with a bitmap to assist in locating + which FIFOs have ready tasks on them. + +RTEMS currently includes multiple priority based scheduling algorithms +as well as other algorithms which incorporate deadline. Each algorithm +is discussed in the following sections. + +Deterministic Priority Scheduler +-------------------------------- + +This is the scheduler implementation which has always been in RTEMS. +After the 4.10 release series, it was factored into pluggable scheduler +selection. It schedules tasks using a priority based algorithm which +takes into account preemption. It is implemented using an array of FIFOs +with a FIFO per priority. It maintains a bitmap which is used to track +which priorities have ready tasks. + +This algorithm is deterministic (e.g. predictable and fixed) in execution +time. This comes at the cost of using slightly over three (3) kilobytes +of RAM on a system configured to support 256 priority levels. + +This scheduler is only aware of a single core. + +Simple Priority Scheduler +------------------------- + +This scheduler implementation has the same behaviour as the Deterministic +Priority Scheduler but uses only one linked list to manage all ready +tasks. When a task is readied, a linear search of that linked list is +performed to determine where to insert the newly readied task. + +This algorithm uses much less RAM than the Deterministic Priority +Scheduler but is *O(n)* where *n* is the number of ready tasks. +In a small system with a small number of tasks, this will not be a +performance issue. Reducing RAM consumption is often critical in small +systems which are incapable of supporting a large number of tasks. + +This scheduler is only aware of a single core. + +Simple SMP Priority Scheduler +----------------------------- + +This scheduler is based upon the Simple Priority Scheduler and is designed +to have the same behaviour on a single core system. But this scheduler +is capable of scheduling threads across multiple cores in an SMP system. +When given a choice of replacing one of two threads at equal priority +on different cores, this algorithm favors replacing threads which are +preemptible and have executed the longest. + +This algorithm is non-deterministic. When scheduling, it must consider +which tasks are to be executed on each core while avoiding superfluous +task migrations. + +Earliest Deadline First Scheduler +--------------------------------- +.. index:: earliest deadline first scheduling + +This is an alternative scheduler in RTEMS for single core applications. +The primary EDF advantage is high total CPU utilization (theoretically +up to 100%). It assumes that tasks have priorities equal to deadlines. + +This EDF is initially preemptive, however, individual tasks may be declared +not-preemptive. Deadlines are declared using only Rate Monotonic manager which +goal is to handle periodic behavior. Period is always equal to deadline. All +ready tasks reside in a single ready queue implemented using a red-black tree. + +This implementation of EDF schedules two different types of task +priority types while each task may switch between the two types within +its execution. If a task does have a deadline declared using the Rate +Monotonic manager, the task is deadline-driven and its priority is equal +to deadline. On the contrary if a task does not have any deadline or +the deadline is cancelled using the Rate Monotonic manager, the task is +considered a background task with priority equal to that assigned +upon initialization in the same manner as for priority scheduler. Each +background task is of a lower importance than each deadline-driven one +and is scheduled when no deadline-driven task and no higher priority +background task is ready to run. + +Every deadline-driven scheduling algorithm requires means for tasks +to claim a deadline. The Rate Monotonic Manager is responsible for +handling periodic execution. In RTEMS periods are equal to deadlines, +thus if a task announces a period, it has to be finished until the +end of this period. The call of ``rtems_rate_monotonic_period`` +passes the scheduler the length of oncoming deadline. Moreover, the``rtems_rate_monotonic_cancel`` and ``rtems_rate_monotonic_delete`` +calls clear the deadlines assigned to the task. + +Constant Bandwidth Server Scheduling (CBS) +------------------------------------------ +.. index:: constant bandwidth server scheduling + +This is an alternative scheduler in RTEMS for single core applications. +The CBS is a budget aware extension of EDF scheduler. The main goal of this +scheduler is to ensure temporal isolation of tasks meaning that a task’s +execution in terms of meeting deadlines must not be influenced by other +tasks as if they were run on multiple independent processors. + +Each task can be assigned a server (current implementation supports only +one task per server). The server is characterized by period (deadline) +and computation time (budget). The ratio budget/period yields bandwidth, +which is the fraction of CPU to be reserved by the scheduler for each +subsequent period. + +The CBS is equipped with a set of rules applied to tasks attached to servers +ensuring that deadline miss because of another task cannot occur. +In case a task breaks one of the rules, its priority is pulled to background +until the end of its period and then restored again. The rules are: + +- Task cannot exceed its registered budget, + +- Task cannot be + unblocked when a ratio between remaining budget and remaining deadline + is higher than declared bandwidth. + +The CBS provides an extensive API. Unlike EDF, the``rtems_rate_monotonic_period`` does not declare a deadline because +it is carried out using CBS API. This call only announces next period. + +Scheduling Modification Mechanisms +================================== + +.. index:: scheduling mechanisms + +RTEMS provides four mechanisms which allow the user to alter the task +scheduling decisions: + +- user-selectable task priority level + +- task preemption control + +- task timeslicing control + +- manual round-robin selection + +Each of these methods provides a powerful capability to customize sets +of tasks to satisfy the unique and particular requirements encountered +in custom real-time applications. Although each mechanism operates +independently, there is a precedence relationship which governs the +effects of scheduling modifications. The evaluation order for scheduling +characteristics is always priority, preemption mode, and timeslicing. +When reading the descriptions of timeslicing and manual round-robin +it is important to keep in mind that preemption (if enabled) of a task +by higher priority tasks will occur as required, overriding the other +factors presented in the description. + +Task Priority and Scheduling +---------------------------- +.. index:: task priority + +The most significant task scheduling modification mechanism is the ability +for the user to assign a priority level to each individual task when it +is created and to alter a task’s priority at run-time. RTEMS supports +up to 255 priority levels. Level 255 is the lowest priority and level +1 is the highest. + +Preemption +----------.. index:: preemption + +Another way the user can alter the basic scheduling algorithm is by +manipulating the preemption mode flag (``RTEMS_PREEMPT_MASK``) +of individual tasks. If preemption is disabled for a task +(``RTEMS_NO_PREEMPT``), then the task will not relinquish +control of the processor until it terminates, blocks, or re-enables +preemption. Even tasks which become ready to run and possess higher +priority levels will not be allowed to execute. Note that the preemption +setting has no effect on the manner in which a task is scheduled. +It only applies once a task has control of the processor. + +Timeslicing +-----------.. index:: timeslicing +.. index:: round robin scheduling + +Timeslicing or round-robin scheduling is an additional method which +can be used to alter the basic scheduling algorithm. Like preemption, +timeslicing is specified on a task by task basis using the timeslicing +mode flag (``RTEMS_TIMESLICE_MASK``). If timeslicing is +enabled for a task (``RTEMS_TIMESLICE``), then RTEMS will +limit the amount of time the task can execute before the processor is +allocated to another task. Each tick of the real-time clock reduces +the currently running task’s timeslice. When the execution time equals +the timeslice, RTEMS will dispatch another task of the same priority +to execute. If there are no other tasks of the same priority ready to +execute, then the current task is allocated an additional timeslice and +continues to run. Remember that a higher priority task will preempt +the task (unless preemption is disabled) as soon as it is ready to run, +even if the task has not used up its entire timeslice. + +Manual Round-Robin +------------------.. index:: manual round robin + +The final mechanism for altering the RTEMS scheduling algorithm is +called manual round-robin. Manual round-robin is invoked by using the``rtems_task_wake_after`` directive with a time interval +of ``RTEMS_YIELD_PROCESSOR``. This allows a task to give +up the processor and be immediately returned to the ready chain at the +end of its priority group. If no other tasks of the same priority are +ready to run, then the task does not lose control of the processor. + +Dispatching Tasks +=================.. index:: dispatching + +The dispatcher is the RTEMS component responsible for +allocating the processor to a ready task. In order to allocate +the processor to one task, it must be deallocated or retrieved +from the task currently using it. This involves a concept +called a context switch. To perform a context switch, the +dispatcher saves the context of the current task and restores +the context of the task which has been allocated to the +processor. Saving and restoring a task’s context is the +storing/loading of all the essential information about a task to +enable it to continue execution without any effects of the +interruption. For example, the contents of a task’s register +set must be the same when it is given the processor as they were +when it was taken away. All of the information that must be +saved or restored for a context switch is located either in the +TCB or on the task’s stacks. + +Tasks that utilize a numeric coprocessor and are created with the``RTEMS_FLOATING_POINT`` attribute require additional +operations during a context switch. These additional operations +are necessary to save and restore the floating point context of``RTEMS_FLOATING_POINT`` tasks. To avoid unnecessary save +and restore operations, the state of the numeric coprocessor is only +saved when a ``RTEMS_FLOATING_POINT`` task is dispatched +and that task was not the last task to utilize the coprocessor. + +Task State Transitions +======================.. index:: task state transitions + +Tasks in an RTEMS system must always be in one of the +five allowable task states. These states are: executing, ready, +blocked, dormant, and non-existent. + +A task occupies the non-existent state before +a ``rtems_task_create`` has been issued on its behalf. +A task enters the non-existent state from any other state in the system +when it is deleted with the ``rtems_task_delete`` directive. +While a task occupies this state it does not have a TCB or a task ID +assigned to it; therefore, no other tasks in the system may reference +this task. + +When a task is created via the ``rtems_task_create`` +directive it enters the dormant state. This state is not entered through +any other means. Although the task exists in the system, it cannot +actively compete for system resources. It will remain in the dormant +state until it is started via the ``rtems_task_start`` +directive, at which time it enters the ready state. The task is now +permitted to be scheduled for the processor and to compete for other +system resources. + +.. code:: c + + +-------------------------------------------------------------+ + | Non-existent | + | +-------------------------------------------------------+ | + | | | | + | | | | + | | Creating +---------+ Deleting | | + | | -------------------> | Dormant | -------------------> | | + | | +---------+ | | + | | | | | + | | Starting | | | + | | | | | + | | V Deleting | | + | | +-------> +-------+ -------------------> | | + | | Yielding / +----- | Ready | ------+ | | + | | / / +-------+ <--+ \\ | | + | | / / \\ \\ Blocking | | + | | / / Dispatching Readying \\ \\ | | + | | / V \\ V | | + | | +-----------+ Blocking +---------+ | | + | | | Executing | --------------> | Blocked | | | + | | +-----------+ +---------+ | | + | | | | + | | | | + | +-------------------------------------------------------+ | + | Non-existent | + +-------------------------------------------------------------+ + +A task occupies the blocked state whenever it is unable to be scheduled +to run. A running task may block itself or be blocked by other tasks in +the system. The running task blocks itself through voluntary operations +that cause the task to wait. The only way a task can block a task other +than itself is with the ``rtems_task_suspend`` directive. +A task enters the blocked state due to any of the following conditions: + +- A task issues a ``rtems_task_suspend`` directive + which blocks either itself or another task in the system. + +- The running task issues a ``rtems_barrier_wait`` + directive. + +- The running task issues a ``rtems_message_queue_receive`` + directive with the wait option and the message queue is empty. + +- The running task issues an ``rtems_event_receive`` + directive with the wait option and the currently pending events do not + satisfy the request. + +- The running task issues a ``rtems_semaphore_obtain`` + directive with the wait option and the requested semaphore is unavailable. + +- The running task issues a ``rtems_task_wake_after`` + directive which blocks the task for the given time interval. If the time + interval specified is zero, the task yields the processor and remains + in the ready state. + +- The running task issues a ``rtems_task_wake_when`` + directive which blocks the task until the requested date and time arrives. + +- The running task issues a ``rtems_rate_monotonic_period`` + directive and must wait for the specified rate monotonic period + to conclude. + +- The running task issues a ``rtems_region_get_segment`` + directive with the wait option and there is not an available segment large + enough to satisfy the task’s request. + +A blocked task may also be suspended. Therefore, both the suspension +and the blocking condition must be removed before the task becomes ready +to run again. + +A task occupies the ready state when it is able to be scheduled to run, +but currently does not have control of the processor. Tasks of the same +or higher priority will yield the processor by either becoming blocked, +completing their timeslice, or being deleted. All tasks with the same +priority will execute in FIFO order. A task enters the ready state due +to any of the following conditions: + +- A running task issues a ``rtems_task_resume`` + directive for a task that is suspended and the task is not blocked + waiting on any resource. + +- A running task issues a ``rtems_message_queue_send``,``rtems_message_queue_broadcast``, or a``rtems_message_queue_urgent`` directive + which posts a message to the queue on which the blocked task is + waiting. + +- A running task issues an ``rtems_event_send`` + directive which sends an event condition to a task which is blocked + waiting on that event condition. + +- A running task issues a ``rtems_semaphore_release`` + directive which releases the semaphore on which the blocked task is + waiting. + +- A timeout interval expires for a task which was blocked + by a call to the ``rtems_task_wake_after`` directive. + +- A timeout period expires for a task which blocked by a + call to the ``rtems_task_wake_when`` directive. + +- A running task issues a ``rtems_region_return_segment`` + directive which releases a segment to the region on which the blocked task + is waiting and a resulting segment is large enough to satisfy + the task’s request. + +- A rate monotonic period expires for a task which blocked + by a call to the ``rtems_rate_monotonic_period`` directive. + +- A timeout interval expires for a task which was blocked + waiting on a message, event, semaphore, or segment with a + timeout specified. + +- A running task issues a directive which deletes a + message queue, a semaphore, or a region on which the blocked + task is waiting. + +- A running task issues a ``rtems_task_restart`` + directive for the blocked task. + +- The running task, with its preemption mode enabled, may + be made ready by issuing any of the directives that may unblock + a task with a higher priority. This directive may be issued + from the running task itself or from an ISR. + A ready task occupies the executing state when it has + control of the CPU. A task enters the executing state due to + any of the following conditions: + +- The task is the highest priority ready task in the + system. + +- The running task blocks and the task is next in the + scheduling queue. The task may be of equal priority as in + round-robin scheduling or the task may possess the highest + priority of the remaining ready tasks. + +- The running task may reenable its preemption mode and a + task exists in the ready queue that has a higher priority than + the running task. + +- The running task lowers its own priority and another + task is of higher priority as a result. + +- The running task raises the priority of a task above its + own and the running task is in preemption mode. + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Initialization Manager +###################### + +Introduction +============ + +The Initialization Manager is responsible for +initiating and shutting down RTEMS. Initiating RTEMS involves +creating and starting all configured initialization tasks, and +for invoking the initialization routine for each user-supplied +device driver. In a multiprocessor configuration, this manager +also initializes the interprocessor communications layer. The +directives provided by the Initialization Manager are: + +- ``rtems_initialize_executive`` - Initialize RTEMS + +- ``rtems_shutdown_executive`` - Shutdown RTEMS + +Background +========== + +Initialization Tasks +-------------------- +.. index:: initialization tasks + +Initialization task(s) are the mechanism by which +RTEMS transfers initial control to the user’s application. +Initialization tasks differ from other application tasks in that +they are defined in the User Initialization Tasks Table and +automatically created and started by RTEMS as part of its +initialization sequence. Since the initialization tasks are +scheduled using the same algorithm as all other RTEMS tasks, +they must be configured at a priority and mode which will ensure +that they will complete execution before other application tasks +execute. Although there is no upper limit on the number of +initialization tasks, an application is required to define at +least one. + +A typical initialization task will create and start +the static set of application tasks. It may also create any +other objects used by the application. Initialization tasks +which only perform initialization should delete themselves upon +completion to free resources for other tasks. Initialization +tasks may transform themselves into a "normal" application task. +This transformation typically involves changing priority and +execution mode. RTEMS does not automatically delete the +initialization tasks. + +System Initialization +--------------------- + +System Initialization begins with board reset and continues +through RTEMS initialization, initialization of all device +drivers, and eventually a context switch to the first user +task. Remember, that interrupts are disabled during +initialization and the *initialization context* is not +a task in any sense and the user should be very careful +during initialization. + +The BSP must ensure that the there is enough stack +space reserved for the initialization context to +successfully execute the initialization routines for +all device drivers and, in multiprocessor configurations, the +Multiprocessor Communications Interface Layer initialization +routine. + +The Idle Task +------------- + +The Idle Task is the lowest priority task in a system +and executes only when no other task is ready to execute. This +default implementation of this task consists of an infinite +loop. RTEMS allows the Idle Task body to be replaced by a CPU +specific implementation, a BSP specific implementation or an +application specific implementation. + +The Idle Task is preemptible and *WILL* be preempted when +any other task is made ready to execute. This characteristic is +critical to the overall behavior of any application. + +Initialization Manager Failure +------------------------------ + +The ``rtems_fatal_error_occurred`` directive will +be invoked from ``rtems_initialize_executive`` +for any of the following reasons: + +- If either the Configuration Table or the CPU Dependent + Information Table is not provided. + +- If the starting address of the RTEMS RAM Workspace, + supplied by the application in the Configuration Table, is NULL + or is not aligned on a four-byte boundary. + +- If the size of the RTEMS RAM Workspace is not large + enough to initialize and configure the system. + +- If the interrupt stack size specified is too small. + +- If multiprocessing is configured and the node entry in + the Multiprocessor Configuration Table is not between one and + the maximum_nodes entry. + +- If a multiprocessor system is being configured and no + Multiprocessor Communications Interface is specified. + +- If no user initialization tasks are configured. At + least one initialization task must be configured to allow RTEMS + to pass control to the application at the end of the executive + initialization sequence. + +- If any of the user initialization tasks cannot be + created or started successfully. + +A discussion of RTEMS actions when a fatal error occurs +may be found `Announcing a Fatal Error`_. + +Operations +========== + +Initializing RTEMS +------------------ + +The Initialization Manager ``rtems_initialize_executive`` +directives is called by the ``boot_card`` routine. The ``boot_card`` +routine is invoked by the Board Support Package once a basic C run-time +environment is set up. This consists of + +- a valid and accessible text section, read-only data, read-write data and + zero-initialized data, + +- an initialization stack large enough to initialize the rest of the Board + Support Package, RTEMS and the device drivers, + +- all registers and components mandated by Application Binary Interface, and + +- disabled interrupts. + +The ``rtems_initialize_executive`` directive uses a system +initialization linker set to initialize only those parts of the overall RTEMS +feature set that is necessary for a particular application. See `Linker Sets`_. +Each RTEMS feature used the application may optionally register an +initialization handler. The system initialization API is available via``#included ``. + +A list of all initialization steps follows. Some steps are optional depending +on the requested feature set of the application. The initialization steps are +execute in the order presented here. + +:dfn:`RTEMS_SYSINIT_BSP_WORK_AREAS` + The work areas consisting of C Program Heap and the RTEMS Workspace are + initialized by the Board Support Package. This step is mandatory. + +:dfn:`RTEMS_SYSINIT_BSP_START` + Basic initialization step provided by the Board Support Package. This step is + mandatory. + +:dfn:`RTEMS_SYSINIT_DATA_STRUCTURES` + This directive is called when the Board Support Package has completed its basic + initialization and allows RTEMS to initialize the application environment based + upon the information in the Configuration Table, User Initialization Tasks + Table, Device Driver Table, User Extension Table, Multiprocessor Configuration + Table, and the Multiprocessor Communications Interface (MPCI) Table. + +:dfn:`RTEMS_SYSINIT_BSP_LIBC` + Depending on the application configuration the IO library and root filesystem + is initialized. This step is mandatory. + +:dfn:`RTEMS_SYSINIT_BEFORE_DRIVERS` + This directive performs initialization that must occur between basis RTEMS data + structure initialization and device driver initialization. In particular, in a + multiprocessor configuration, this directive will create the MPCI Server Task. + +:dfn:`RTEMS_SYSINIT_BSP_PRE_DRIVERS` + Initialization step performed right before device drivers are initialized + provided by the Board Support Package. This step is mandatory. + +:dfn:`RTEMS_SYSINIT_DEVICE_DRIVERS` + This step initializes all statically configured device drivers and performs all + RTEMS initialization which requires device drivers to be initialized. This + step is mandatory. + In a multiprocessor configuration, this service will initialize the + Multiprocessor Communications Interface (MPCI) and synchronize with the other + nodes in the system. + +:dfn:`RTEMS_SYSINIT_BSP_POST_DRIVERS` + Initialization step performed right after device drivers are initialized + provided by the Board Support Package. This step is mandatory. + +The final action of the ``rtems_initialize_executive`` directive +is to start multitasking. RTEMS does not return to the initialization context +and the initialization stack may be re-used for interrupt processing. + +Many of RTEMS actions during initialization are based upon +the contents of the Configuration Table. For more information +regarding the format and contents of this table, please refer +to the chapter `Configuring a System`_. + +The final action in the initialization sequence is the +initiation of multitasking. When the scheduler and dispatcher +are enabled, the highest priority, ready task will be dispatched +to run. Control will not be returned to the Board Support +Package after multitasking is enabled. The initialization stack may be re-used +for interrupt processing. + +Shutting Down RTEMS +------------------- + +The ``rtems_shutdown_executive`` directive is invoked by the +application to end multitasking and terminate the system. + +Directives +========== + +This section details the Initialization Manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +INITIALIZE_EXECUTIVE - Initialize RTEMS +--------------------------------------- +.. index:: initialize RTEMS +.. index:: start multitasking + +**CALLING SEQUENCE:** + +.. index:: rtems_initialize_executive + +.. code:: c + + void rtems_initialize_executive(void); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +Iterates through the system initialization linker set and invokes the +registered handlers. The final step is to start multitasking. + +**NOTES:** + +This directive should be called by ``boot_card`` only. + +This directive *does not return* to the caller. Errors in the initialization +sequence are usually fatal and lead to a system termination. + +SHUTDOWN_EXECUTIVE - Shutdown RTEMS +----------------------------------- +.. index:: shutdown RTEMS + +**CALLING SEQUENCE:** + +.. index:: rtems_shutdown_executive + +.. code:: c + + void rtems_shutdown_executive( + uint32_t result + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive is called when the application wishes to shutdown RTEMS. The +system is terminated with a fatal source of ``RTEMS_FATAL_SOURCE_EXIT`` and +the specified ``result`` code. + +**NOTES:** + +This directive *must* be the last RTEMS directive +invoked by an application and it *does not return* to the caller. + +This directive may be called any time. + +.. COMMENT: COPYRIGHT (c) 1988-2014. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Task Manager +############ + +.. index:: tasks + +Introduction +============ + +The task manager provides a comprehensive set of directives to +create, delete, and administer tasks. The directives provided +by the task manager are: + +- ``rtems_task_create`` - Create a task + +- ``rtems_task_ident`` - Get ID of a task + +- ``rtems_task_self`` - Obtain ID of caller + +- ``rtems_task_start`` - Start a task + +- ``rtems_task_restart`` - Restart a task + +- ``rtems_task_delete`` - Delete a task + +- ``rtems_task_suspend`` - Suspend a task + +- ``rtems_task_resume`` - Resume a task + +- ``rtems_task_is_suspended`` - Determine if a task is suspended + +- ``rtems_task_set_priority`` - Set task priority + +- ``rtems_task_mode`` - Change current task’s mode + +- ``rtems_task_wake_after`` - Wake up after interval + +- ``rtems_task_wake_when`` - Wake up when specified + +- ``rtems_iterate_over_all_threads`` - Iterate Over Tasks + +- ``rtems_task_variable_add`` - Associate per task variable + +- ``rtems_task_variable_get`` - Obtain value of a a per task variable + +- ``rtems_task_variable_delete`` - Remove per task variable + +Background +========== + +Task Definition +--------------- +.. index:: task, definition + +Many definitions of a task have been proposed in computer literature. +Unfortunately, none of these definitions encompasses all facets of the +concept in a manner which is operating system independent. Several of the +more common definitions are provided to enable each user to select a +definition which best matches their own experience and understanding of the +task concept: + +- a "dispatchable" unit. + +- an entity to which the processor is allocated. + +- an atomic unit of a real-time, multiprocessor system. + +- single threads of execution which concurrently compete for resources. + +- a sequence of closely related computations which can execute + concurrently with other computational sequences. + +From RTEMS’ perspective, a task is the smallest thread of +execution which can compete on its own for system resources. A +task is manifested by the existence of a task control block +(TCB). + +Task Control Block +------------------ + +The Task Control Block (TCB) is an RTEMS defined data structure +which contains all the information that is pertinent to the +execution of a task. During system initialization, RTEMS +reserves a TCB for each task configured. A TCB is allocated +upon creation of the task and is returned to the TCB free list +upon deletion of the task. + +The TCB’s elements are modified as a result of system calls made +by the application in response to external and internal stimuli. +TCBs are the only RTEMS internal data structure that can be +accessed by an application via user extension routines. The TCB +contains a task’s name, ID, current priority, current and +starting states, execution mode, TCB user extension pointer, +scheduling control structures, as well as data required by a +blocked task. + +A task’s context is stored in the TCB when a task switch occurs. +When the task regains control of the processor, its context is +restored from the TCB. When a task is restarted, the initial +state of the task is restored from the starting context area in +the task’s TCB. + +Task States +----------- +.. index:: task states + +A task may exist in one of the following five states: + +- *executing* - Currently scheduled to the CPU + +- *ready* - May be scheduled to the CPU + +- *blocked* - Unable to be scheduled to the CPU + +- *dormant* - Created task that is not started + +- *non-existent* - Uncreated or deleted task + +An active task may occupy the executing, ready, blocked or +dormant state, otherwise the task is considered non-existent. +One or more tasks may be active in the system simultaneously. +Multiple tasks communicate, synchronize, and compete for system +resources with each other via system calls. The multiple tasks +appear to execute in parallel, but actually each is dispatched +to the CPU for periods of time determined by the RTEMS +scheduling algorithm. The scheduling of a task is based on its +current state and priority. + +Task Priority +------------- +.. index:: task priority +.. index:: priority, task +.. index:: rtems_task_priority + +A task’s priority determines its importance in relation to the +other tasks executing on the same processor. RTEMS supports 255 +levels of priority ranging from 1 to 255. The data type``rtems_task_priority`` is used to store task +priorities. + +Tasks of numerically +smaller priority values are more important tasks than tasks of +numerically larger priority values. For example, a task at +priority level 5 is of higher privilege than a task at priority +level 10. There is no limit to the number of tasks assigned to +the same priority. + +Each task has a priority associated with it at all times. The +initial value of this priority is assigned at task creation +time. The priority of a task may be changed at any subsequent +time. + +Priorities are used by the scheduler to determine which ready +task will be allowed to execute. In general, the higher the +logical priority of a task, the more likely it is to receive +processor execution time. + +Task Mode +--------- +.. index:: task mode +.. index:: rtems_task_mode + +A task’s execution mode is a combination of the following +four components: + +- preemption + +- ASR processing + +- timeslicing + +- interrupt level + +It is used to modify RTEMS’ scheduling process and to alter the +execution environment of the task. The data type``rtems_task_mode`` is used to manage the task +execution mode... index:: preemption + +The preemption component allows a task to determine when control of the +processor is relinquished. If preemption is disabled +(``RTEMS_NO_PREEMPT``), the task will retain control of the +processor as long as it is in the executing state – even if a higher +priority task is made ready. If preemption is enabled +(``RTEMS_PREEMPT``) and a higher priority task is made ready, +then the processor will be taken away from the current task immediately and +given to the higher priority task... index:: timeslicing + +The timeslicing component is used by the RTEMS scheduler to determine how +the processor is allocated to tasks of equal priority. If timeslicing is +enabled (``RTEMS_TIMESLICE``), then RTEMS will limit the amount +of time the task can execute before the processor is allocated to another +ready task of equal priority. The length of the timeslice is application +dependent and specified in the Configuration Table. If timeslicing is +disabled (``RTEMS_NO_TIMESLICE``), then the task will be +allowed to execute until a task of higher priority is made ready. If``RTEMS_NO_PREEMPT`` is selected, then the timeslicing +component is ignored by the scheduler. + +The asynchronous signal processing component is used to determine when +received signals are to be processed by the task. +If signal processing is enabled (``RTEMS_ASR``), then signals +sent to the task will be processed the next time the task executes. If +signal processing is disabled (``RTEMS_NO_ASR``), then all +signals received by the task will remain posted until signal processing is +enabled. This component affects only tasks which have established a +routine to process asynchronous signals... index:: interrupt level, task + +The interrupt level component is used to determine which +interrupts will be enabled when the task is executing.``RTEMS_INTERRUPT_LEVEL(n)`` +specifies that the task will execute at interrupt level n. + +- ``RTEMS_PREEMPT`` - enable preemption (default) + +- ``RTEMS_NO_PREEMPT`` - disable preemption + +- ``RTEMS_NO_TIMESLICE`` - disable timeslicing (default) + +- ``RTEMS_TIMESLICE`` - enable timeslicing + +- ``RTEMS_ASR`` - enable ASR processing (default) + +- ``RTEMS_NO_ASR`` - disable ASR processing + +- ``RTEMS_INTERRUPT_LEVEL(0)`` - enable all interrupts (default) + +- ``RTEMS_INTERRUPT_LEVEL(n)`` - execute at interrupt level n + +The set of default modes may be selected by specifying the``RTEMS_DEFAULT_MODES`` constant. + +Accessing Task Arguments +------------------------ +.. index:: task arguments +.. index:: task prototype + +All RTEMS tasks are invoked with a single argument which is +specified when they are started or restarted. The argument is +commonly used to communicate startup information to the task. +The simplest manner in which to define a task which accesses it +argument is:.. index:: rtems_task + +.. code:: c + + rtems_task user_task( + rtems_task_argument argument + ); + +Application tasks requiring more information may view this +single argument as an index into an array of parameter blocks. + +Floating Point Considerations +----------------------------- +.. index:: floating point + +Creating a task with the ``RTEMS_FLOATING_POINT`` attribute +flag results +in additional memory being allocated for the TCB to store the state of the +numeric coprocessor during task switches. This additional memory is*NOT* allocated for ``RTEMS_NO_FLOATING_POINT`` tasks. Saving +and restoring the context of a ``RTEMS_FLOATING_POINT`` task +takes longer than that of a ``RTEMS_NO_FLOATING_POINT`` task +because of the relatively large amount of time required for the numeric +coprocessor to save or restore its computational state. + +Since RTEMS was designed specifically for embedded military applications +which are floating point intensive, the executive is optimized to avoid +unnecessarily saving and restoring the state of the numeric coprocessor. +The state of the numeric coprocessor is only saved when a``RTEMS_FLOATING_POINT`` task is dispatched and that task was +not the last task to utilize the coprocessor. In a system with only one``RTEMS_FLOATING_POINT`` task, the state of the numeric +coprocessor will never be saved or restored. + +Although the overhead imposed by ``RTEMS_FLOATING_POINT`` tasks +is minimal, some applications may wish to completely avoid the overhead +associated with ``RTEMS_FLOATING_POINT`` tasks and still +utilize a numeric coprocessor. By preventing a task from being preempted +while performing a sequence of floating point operations, a``RTEMS_NO_FLOATING_POINT`` task can utilize the numeric +coprocessor without incurring the overhead of a``RTEMS_FLOATING_POINT`` context switch. This approach also +avoids the allocation of a floating point context area. However, if this +approach is taken by the application designer, NO tasks should be created +as ``RTEMS_FLOATING_POINT`` tasks. Otherwise, the floating +point context will not be correctly maintained because RTEMS assumes that +the state of the numeric coprocessor will not be altered by``RTEMS_NO_FLOATING_POINT`` tasks. + +If the supported processor type does not have hardware floating +capabilities or a standard numeric coprocessor, RTEMS will not provide +built-in support for hardware floating point on that processor. In this +case, all tasks are considered ``RTEMS_NO_FLOATING_POINT`` +whether created as ``RTEMS_FLOATING_POINT`` or``RTEMS_NO_FLOATING_POINT`` tasks. A floating point emulation +software library must be utilized for floating point operations. + +On some processors, it is possible to disable the floating point unit +dynamically. If this capability is supported by the target processor, then +RTEMS will utilize this capability to enable the floating point unit only +for tasks which are created with the ``RTEMS_FLOATING_POINT`` +attribute. The consequence of a ``RTEMS_NO_FLOATING_POINT`` +task attempting to access the floating point unit is CPU dependent but will +generally result in an exception condition. + +Per Task Variables +------------------ +.. index:: per task variables + +Per task variables are deprecated, see the warning below. + +Per task variables are used to support global variables whose value +may be unique to a task. After indicating that a variable should be +treated as private (i.e. per-task) the task can access and modify the +variable, but the modifications will not appear to other tasks, and +other tasks’ modifications to that variable will not affect the value +seen by the task. This is accomplished by saving and restoring the +variable’s value each time a task switch occurs to or from the calling task. + +The value seen by other tasks, including those which have not added the +variable to their set and are thus accessing the variable as a common +location shared among tasks, cannot be affected by a task once it has +added a variable to its local set. Changes made to the variable by +other tasks will not affect the value seen by a task which has added the +variable to its private set. + +This feature can be used when a routine is to be spawned repeatedly as +several independent tasks. Although each task will have its own stack, +and thus separate stack variables, they will all share the same static and +global variables. To make a variable not shareable (i.e. a "global" variable +that is specific to a single task), the tasks can call``rtems_task_variable_add`` to make a separate copy of the variable +for each task, but all at the same physical address. + +Task variables increase the context switch time to and from the +tasks that own them so it is desirable to minimize the number of +task variables. One efficient method is to have a single task +variable that is a pointer to a dynamically allocated structure +containing the task’s private "global" data. + +A critical point with per-task variables is that each task must separately +request that the same global variable is per-task private. + +*WARNING*: Per-Task variables are inherently broken on SMP systems. They +only work correctly when there is one task executing in the system and +that task is the logical owner of the value in the per-task variable’s +location. There is no way for a single memory image to contain the +correct value for each task executing on each core. Consequently, +per-task variables are disabled in SMP configurations of RTEMS. +Instead the application developer should +consider the use of POSIX Keys or Thread Local Storage (TLS). POSIX Keys +are not enabled in all RTEMS configurations. + +Building a Task Attribute Set +----------------------------- +.. index:: task attributes, building + +In general, an attribute set is built by a bitwise OR of the +desired components. The set of valid task attribute components +is listed below: + +- ``RTEMS_NO_FLOATING_POINT`` - does not use coprocessor (default) + +- ``RTEMS_FLOATING_POINT`` - uses numeric coprocessor + +- ``RTEMS_LOCAL`` - local task (default) + +- ``RTEMS_GLOBAL`` - global task + +Attribute values are specifically designed to be mutually +exclusive, therefore bitwise OR and addition operations are +equivalent as long as each attribute appears exactly once in the +component list. A component listed as a default is not required +to appear in the component list, although it is a good +programming practice to specify default components. If all +defaults are desired, then ``RTEMS_DEFAULT_ATTRIBUTES`` should be used. + +This example demonstrates the attribute_set parameter needed to +create a local task which utilizes the numeric coprocessor. The +attribute_set parameter could be ``RTEMS_FLOATING_POINT`` or``RTEMS_LOCAL | RTEMS_FLOATING_POINT``. +The attribute_set parameter can be set to``RTEMS_FLOATING_POINT`` because ``RTEMS_LOCAL`` is the default for all created +tasks. If the task were global and used the numeric +coprocessor, then the attribute_set parameter would be``RTEMS_GLOBAL | RTEMS_FLOATING_POINT``. + +Building a Mode and Mask +------------------------ +.. index:: task mode, building + +In general, a mode and its corresponding mask is built by a +bitwise OR of the desired components. The set of valid mode +constants and each mode’s corresponding mask constant is +listed below: + +- ``RTEMS_PREEMPT`` is masked by``RTEMS_PREEMPT_MASK`` and enables preemption + +- ``RTEMS_NO_PREEMPT`` is masked by``RTEMS_PREEMPT_MASK`` and disables preemption + +- ``RTEMS_NO_TIMESLICE`` is masked by``RTEMS_TIMESLICE_MASK`` and disables timeslicing + +- ``RTEMS_TIMESLICE`` is masked by``RTEMS_TIMESLICE_MASK`` and enables timeslicing + +- ``RTEMS_ASR`` is masked by``RTEMS_ASR_MASK`` and enables ASR processing + +- ``RTEMS_NO_ASR`` is masked by``RTEMS_ASR_MASK`` and disables ASR processing + +- ``RTEMS_INTERRUPT_LEVEL(0)`` is masked by``RTEMS_INTERRUPT_MASK`` and enables all interrupts + +- ``RTEMS_INTERRUPT_LEVEL(n)`` is masked by``RTEMS_INTERRUPT_MASK`` and sets interrupts level n + +Mode values are specifically designed to be mutually exclusive, therefore +bitwise OR and addition operations are equivalent as long as each mode +appears exactly once in the component list. A mode component listed as a +default is not required to appear in the mode component list, although it +is a good programming practice to specify default components. If all +defaults are desired, the mode ``RTEMS_DEFAULT_MODES`` and the +mask ``RTEMS_ALL_MODE_MASKS`` should be used. + +The following example demonstrates the mode and mask parameters used with +the ``rtems_task_mode`` +directive to place a task at interrupt level 3 and make it +non-preemptible. The mode should be set to``RTEMS_INTERRUPT_LEVEL(3) | +RTEMS_NO_PREEMPT`` to indicate the desired preemption mode and +interrupt level, while the mask parameter should be set to``RTEMS_INTERRUPT_MASK | +RTEMS_NO_PREEMPT_MASK`` to indicate that the calling task’s +interrupt level and preemption mode are being altered. + +Operations +========== + +Creating Tasks +-------------- + +The ``rtems_task_create`` +directive creates a task by allocating a task +control block, assigning the task a user-specified name, +allocating it a stack and floating point context area, setting a +user-specified initial priority, setting a user-specified +initial mode, and assigning it a task ID. Newly created tasks +are initially placed in the dormant state. All RTEMS tasks +execute in the most privileged mode of the processor. + +Obtaining Task IDs +------------------ + +When a task is created, RTEMS generates a unique task ID and +assigns it to the created task until it is deleted. The task ID +may be obtained by either of two methods. First, as the result +of an invocation of the ``rtems_task_create`` +directive, the task ID is +stored in a user provided location. Second, the task ID may be +obtained later using the ``rtems_task_ident`` +directive. The task ID is +used by other directives to manipulate this task. + +Starting and Restarting Tasks +----------------------------- + +The ``rtems_task_start`` +directive is used to place a dormant task in the +ready state. This enables the task to compete, based on its +current priority, for the processor and other system resources. +Any actions, such as suspension or change of priority, performed +on a task prior to starting it are nullified when the task is +started. + +With the ``rtems_task_start`` +directive the user specifies the task’s +starting address and argument. The argument is used to +communicate some startup information to the task. As part of +this directive, RTEMS initializes the task’s stack based upon +the task’s initial execution mode and start address. The +starting argument is passed to the task in accordance with the +target processor’s calling convention. + +The ``rtems_task_restart`` +directive restarts a task at its initial +starting address with its original priority and execution mode, +but with a possibly different argument. The new argument may be +used to distinguish between the original invocation of the task +and subsequent invocations. The task’s stack and control block +are modified to reflect their original creation values. +Although references to resources that have been requested are +cleared, resources allocated by the task are NOT automatically +returned to RTEMS. A task cannot be restarted unless it has +previously been started (i.e. dormant tasks cannot be +restarted). All restarted tasks are placed in the ready state. + +Suspending and Resuming Tasks +----------------------------- + +The ``rtems_task_suspend`` +directive is used to place either the caller or +another task into a suspended state. The task remains suspended +until a ``rtems_task_resume`` +directive is issued. This implies that a +task may be suspended as well as blocked waiting either to +acquire a resource or for the expiration of a timer. + +The ``rtems_task_resume`` +directive is used to remove another task from +the suspended state. If the task is not also blocked, resuming +it will place it in the ready state, allowing it to once again +compete for the processor and resources. If the task was +blocked as well as suspended, this directive clears the +suspension and leaves the task in the blocked state. + +Suspending a task which is already suspended or resuming a +task which is not suspended is considered an error. +The ``rtems_task_is_suspended`` can be used to +determine if a task is currently suspended. + +Delaying the Currently Executing Task +------------------------------------- + +The ``rtems_task_wake_after`` directive creates a sleep timer +which allows a task to go to sleep for a specified interval. The task is +blocked until the delay interval has elapsed, at which time the task is +unblocked. A task calling the ``rtems_task_wake_after`` +directive with a delay +interval of ``RTEMS_YIELD_PROCESSOR`` ticks will yield the +processor to any other ready task of equal or greater priority and remain +ready to execute. + +The ``rtems_task_wake_when`` +directive creates a sleep timer which allows +a task to go to sleep until a specified date and time. The +calling task is blocked until the specified date and time has +occurred, at which time the task is unblocked. + +Changing Task Priority +---------------------- + +The ``rtems_task_set_priority`` +directive is used to obtain or change the +current priority of either the calling task or another task. If +the new priority requested is``RTEMS_CURRENT_PRIORITY`` or the task’s +actual priority, then the current priority will be returned and +the task’s priority will remain unchanged. If the task’s +priority is altered, then the task will be scheduled according +to its new priority. + +The ``rtems_task_restart`` +directive resets the priority of a task to its +original value. + +Changing Task Mode +------------------ + +The ``rtems_task_mode`` +directive is used to obtain or change the current +execution mode of the calling task. A task’s execution mode is +used to enable preemption, timeslicing, ASR processing, and to +set the task’s interrupt level. + +The ``rtems_task_restart`` +directive resets the mode of a task to its +original value. + +Task Deletion +------------- + +RTEMS provides the ``rtems_task_delete`` +directive to allow a task to +delete itself or any other task. This directive removes all +RTEMS references to the task, frees the task’s control block, +removes it from resource wait queues, and deallocates its stack +as well as the optional floating point context. The task’s name +and ID become inactive at this time, and any subsequent +references to either of them is invalid. In fact, RTEMS may +reuse the task ID for another task which is created later in the +application. + +Unexpired delay timers (i.e. those used by``rtems_task_wake_after`` and``rtems_task_wake_when``) and +timeout timers associated with the task are +automatically deleted, however, other resources dynamically +allocated by the task are NOT automatically returned to RTEMS. +Therefore, before a task is deleted, all of its dynamically +allocated resources should be deallocated by the user. This may +be accomplished by instructing the task to delete itself rather +than directly deleting the task. Other tasks may instruct a +task to delete itself by sending a "delete self" message, event, +or signal, or by restarting the task with special arguments +which instruct the task to delete itself. + +Transition Advice for Obsolete Directives +----------------------------------------- + +Notepads +~~~~~~~~.. index:: rtems_task_get_note +.. index:: rtems_task_set_note + +Task notepads and the associated directives``rtems_task_get_note`` and``rtems_task_set_note`` were removed after the 4.11 Release +Series. These were never thread-safe to access and subject to conflicting +use of the notepad index by libraries which were designed independently. + +It is recommended that applications be modified to use services +which are thread safe and not subject to issues with multiple applications +conflicting over the key (e.g. notepad index) selection. For most +applications, POSIX Keys should be used. These are available in all RTEMS +build configurations. It is also possible that Thread Local Storage is +an option for some use cases. + +Directives +========== + +This section details the task manager’s directives. A +subsection is dedicated to each of this manager’s directives and +describes the calling sequence, related constants, usage, and +status codes. + +TASK_CREATE - Create a task +--------------------------- +.. index:: create a task + +**CALLING SEQUENCE:** + +.. index:: rtems_task_create + +.. code:: c + + rtems_status_code rtems_task_create( + rtems_name name, + rtems_task_priority initial_priority, + size_t stack_size, + rtems_mode initial_modes, + rtems_attribute attribute_set, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - task created successfully +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - invalid task name +``RTEMS_INVALID_PRIORITY`` - invalid task priority +``RTEMS_MP_NOT_CONFIGURED`` - multiprocessing not configured +``RTEMS_TOO_MANY`` - too many tasks created +``RTEMS_UNSATISFIED`` - not enough memory for stack/FP context +``RTEMS_TOO_MANY`` - too many global objects + +**DESCRIPTION:** + +This directive creates a task which resides on the local node. +It allocates and initializes a TCB, a stack, and an optional +floating point context area. The mode parameter contains values +which sets the task’s initial execution mode. The``RTEMS_FLOATING_POINT`` attribute should be +specified if the created task +is to use a numeric coprocessor. For performance reasons, it is +recommended that tasks not using the numeric coprocessor should +specify the ``RTEMS_NO_FLOATING_POINT`` attribute. +If the ``RTEMS_GLOBAL`` +attribute is specified, the task can be accessed from remote +nodes. The task id, returned in id, is used in other task +related directives to access the task. When created, a task is +placed in the dormant state and can only be made ready to +execute using the directive ``rtems_task_start``. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +Valid task priorities range from a high of 1 to a low of 255. + +If the requested stack size is less than the configured +minimum stack size, then RTEMS will use the configured +minimum as the stack size for this task. In addition +to being able to specify the task stack size as a integer, +there are two constants which may be specified: + +- ``RTEMS_MINIMUM_STACK_SIZE`` + is the minimum stack size *RECOMMENDED* for use on this processor. + This value is selected by the RTEMS developers conservatively to + minimize the risk of blown stacks for most user applications. + Using this constant when specifying the task stack size, indicates + that the stack size will be at least``RTEMS_MINIMUM_STACK_SIZE`` bytes in size. If the + user configured minimum stack size is larger than the recommended + minimum, then it will be used. + +- ``RTEMS_CONFIGURED_MINIMUM_STACK_SIZE`` + indicates that this task is to be created with a stack size + of the minimum stack size that was configured by the application. + If not explicitly configured by the application, the default + configured minimum stack size is the processor dependent value``RTEMS_MINIMUM_STACK_SIZE``. Since this uses + the configured minimum stack size value, you may get a stack + size that is smaller or larger than the recommended minimum. This + can be used to provide large stacks for all tasks on complex + applications or small stacks on applications that are trying + to conserve memory. + +Application developers should consider the stack usage of the +device drivers when calculating the stack size required for +tasks which utilize the driver. + +The following task attribute constants are defined by RTEMS: + +- ``RTEMS_NO_FLOATING_POINT`` - does not use coprocessor (default) + +- ``RTEMS_FLOATING_POINT`` - uses numeric coprocessor + +- ``RTEMS_LOCAL`` - local task (default) + +- ``RTEMS_GLOBAL`` - global task + +The following task mode constants are defined by RTEMS: + +- ``RTEMS_PREEMPT`` - enable preemption (default) + +- ``RTEMS_NO_PREEMPT`` - disable preemption + +- ``RTEMS_NO_TIMESLICE`` - disable timeslicing (default) + +- ``RTEMS_TIMESLICE`` - enable timeslicing + +- ``RTEMS_ASR`` - enable ASR processing (default) + +- ``RTEMS_NO_ASR`` - disable ASR processing + +- ``RTEMS_INTERRUPT_LEVEL(0)`` - enable all interrupts (default) + +- ``RTEMS_INTERRUPT_LEVEL(n)`` - execute at interrupt level n + +The interrupt level portion of the task execution mode +supports a maximum of 256 interrupt levels. These levels are +mapped onto the interrupt levels actually supported by the +target processor in a processor dependent fashion. + +Tasks should not be made global unless remote tasks must +interact with them. This avoids the system overhead incurred by +the creation of a global task. When a global task is created, +the task’s name and id must be transmitted to every node in the +system for insertion in the local copy of the global object +table. + +The total number of global objects, including tasks, is limited +by the maximum_global_objects field in the Configuration Table. + +TASK_IDENT - Get ID of a task +----------------------------- +.. index:: get ID of a task + +**CALLING SEQUENCE:** + +.. index:: rtems_task_ident + +.. code:: c + + rtems_status_code rtems_task_ident( + rtems_name name, + uint32_t node, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - task identified successfully +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - invalid task name +``RTEMS_INVALID_NODE`` - invalid node id + +**DESCRIPTION:** + +This directive obtains the task id associated with the task name +specified in name. A task may obtain its own id by specifying``RTEMS_SELF`` or its own task name in name. If the task name is not +unique, then the task id returned will match one of the tasks +with that name. However, this task id is not guaranteed to +correspond to the desired task. The task id, returned in id, is +used in other task related directives to access the task. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +If node is ``RTEMS_SEARCH_ALL_NODES``, all nodes are searched with the +local node being searched first. All other nodes are searched +with the lowest numbered node searched first. + +If node is a valid node number which does not represent the +local node, then only the tasks exported by the designated node +are searched. + +This directive does not generate activity on remote nodes. It +accesses only the local copy of the global object table. + +TASK_SELF - Obtain ID of caller +------------------------------- +.. index:: obtain ID of caller + +**CALLING SEQUENCE:** + +.. index:: rtems_task_self + +.. code:: c + + rtems_id rtems_task_self(void); + +**DIRECTIVE STATUS CODES:** + +Returns the object Id of the calling task. + +**DESCRIPTION:** + +This directive returns the Id of the calling task. + +**NOTES:** + +If called from an interrupt service routine, this directive +will return the Id of the interrupted task. + +TASK_START - Start a task +------------------------- +.. index:: starting a task + +**CALLING SEQUENCE:** + +.. index:: rtems_task_start + +.. code:: c + + rtems_status_code rtems_task_start( + rtems_id id, + rtems_task_entry entry_point, + rtems_task_argument argument + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - ask started successfully +``RTEMS_INVALID_ADDRESS`` - invalid task entry point +``RTEMS_INVALID_ID`` - invalid task id +``RTEMS_INCORRECT_STATE`` - task not in the dormant state +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - cannot start remote task + +**DESCRIPTION:** + +This directive readies the task, specified by ``id``, for execution +based on the priority and execution mode specified when the task +was created. The starting address of the task is given in``entry_point``. The task’s starting argument is contained in +argument. This argument can be a single value or used as an index into an +array of parameter blocks. The type of this numeric argument is an unsigned +integer type with the property that any valid pointer to void can be converted +to this type and then converted back to a pointer to void. The result will +compare equal to the original pointer. + +**NOTES:** + +The calling task will be preempted if its preemption mode is +enabled and the task being started has a higher priority. + +Any actions performed on a dormant task such as suspension or +change of priority are nullified when the task is initiated via +the ``rtems_task_start`` directive. + +TASK_RESTART - Restart a task +----------------------------- +.. index:: restarting a task + +**CALLING SEQUENCE:** + +.. index:: rtems_task_restart + +.. code:: c + + rtems_status_code rtems_task_restart( + rtems_id id, + rtems_task_argument argument + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - task restarted successfully +``RTEMS_INVALID_ID`` - task id invalid +``RTEMS_INCORRECT_STATE`` - task never started +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - cannot restart remote task + +**DESCRIPTION:** + +This directive resets the task specified by id to begin +execution at its original starting address. The task’s priority +and execution mode are set to the original creation values. If +the task is currently blocked, RTEMS automatically makes the +task ready. A task can be restarted from any state, except the +dormant state. + +The task’s starting argument is contained in argument. This argument can be a +single value or an index into an array of parameter blocks. The type of this +numeric argument is an unsigned integer type with the property that any valid +pointer to void can be converted to this type and then converted back to a +pointer to void. The result will compare equal to the original pointer. This +new argument may be used to distinguish +between the initial ``rtems_task_start`` +of the task and any ensuing calls +to ``rtems_task_restart`` +of the task. This can be beneficial in deleting +a task. Instead of deleting a task using +the ``rtems_task_delete`` +directive, a task can delete another task by restarting that +task, and allowing that task to release resources back to RTEMS +and then delete itself. + +**NOTES:** + +If id is ``RTEMS_SELF``, the calling task will be restarted and will not +return from this directive. + +The calling task will be preempted if its preemption mode is +enabled and the task being restarted has a higher priority. + +The task must reside on the local node, even if the task was +created with the ``RTEMS_GLOBAL`` option. + +TASK_DELETE - Delete a task +--------------------------- +.. index:: deleting a task + +**CALLING SEQUENCE:** + +.. index:: rtems_task_delete + +.. code:: c + + rtems_status_code rtems_task_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - task deleted successfully +``RTEMS_INVALID_ID`` - task id invalid +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - cannot restart remote task + +**DESCRIPTION:** + +This directive deletes a task, either the calling task or +another task, as specified by id. RTEMS stops the execution of +the task and reclaims the stack memory, any allocated delay or +timeout timers, the TCB, and, if the task is ``RTEMS_FLOATING_POINT``, its +floating point context area. RTEMS does not reclaim the +following resources: region segments, partition buffers, +semaphores, timers, or rate monotonic periods. + +**NOTES:** + +A task is responsible for releasing its resources back to RTEMS +before deletion. To insure proper deallocation of resources, a +task should not be deleted unless it is unable to execute or +does not hold any RTEMS resources. If a task holds RTEMS +resources, the task should be allowed to deallocate its +resources before deletion. A task can be directed to release +its resources and delete itself by restarting it with a special +argument or by sending it a message, an event, or a signal. + +Deletion of the current task (``RTEMS_SELF``) will force RTEMS to select +another task to execute. + +When a global task is deleted, the task id must be transmitted +to every node in the system for deletion from the local copy of +the global object table. + +The task must reside on the local node, even if the task was +created with the ``RTEMS_GLOBAL`` option. + +TASK_SUSPEND - Suspend a task +----------------------------- +.. index:: suspending a task + +**CALLING SEQUENCE:** + +.. index:: rtems_task_suspend + +.. code:: c + + rtems_status_code rtems_task_suspend( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - task suspended successfully +``RTEMS_INVALID_ID`` - task id invalid +``RTEMS_ALREADY_SUSPENDED`` - task already suspended + +**DESCRIPTION:** + +This directive suspends the task specified by id from further +execution by placing it in the suspended state. This state is +additive to any other blocked state that the task may already be +in. The task will not execute again until another task issues +the ``rtems_task_resume`` +directive for this task and any blocked state +has been removed. + +**NOTES:** + +The requesting task can suspend itself by specifying ``RTEMS_SELF`` as id. +In this case, the task will be suspended and a successful +return code will be returned when the task is resumed. + +Suspending a global task which does not reside on the local node +will generate a request to the remote node to suspend the +specified task. + +If the task specified by id is already suspended, then the``RTEMS_ALREADY_SUSPENDED`` status code is returned. + +TASK_RESUME - Resume a task +--------------------------- +.. index:: resuming a task + +**CALLING SEQUENCE:** + +.. index:: rtems_task_resume + +.. code:: c + + rtems_status_code rtems_task_resume( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - task resumed successfully +``RTEMS_INVALID_ID`` - task id invalid +``RTEMS_INCORRECT_STATE`` - task not suspended + +**DESCRIPTION:** + +This directive removes the task specified by id from the +suspended state. If the task is in the ready state after the +suspension is removed, then it will be scheduled to run. If the +task is still in a blocked state after the suspension is +removed, then it will remain in that blocked state. + +**NOTES:** + +The running task may be preempted if its preemption mode is +enabled and the local task being resumed has a higher priority. + +Resuming a global task which does not reside on the local node +will generate a request to the remote node to resume the +specified task. + +If the task specified by id is not suspended, then the``RTEMS_INCORRECT_STATE`` status code is returned. + +TASK_IS_SUSPENDED - Determine if a task is Suspended +---------------------------------------------------- +.. index:: is task suspended + +**CALLING SEQUENCE:** + +.. index:: rtems_task_is_suspended + +.. code:: c + + rtems_status_code rtems_task_is_suspended( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - task is NOT suspended +``RTEMS_ALREADY_SUSPENDED`` - task is currently suspended +``RTEMS_INVALID_ID`` - task id invalid +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - not supported on remote tasks + +**DESCRIPTION:** + +This directive returns a status code indicating whether or +not the specified task is currently suspended. + +**NOTES:** + +This operation is not currently supported on remote tasks. + +TASK_SET_PRIORITY - Set task priority +------------------------------------- +.. index:: rtems_task_set_priority +.. index:: current task priority +.. index:: set task priority +.. index:: get task priority +.. index:: obtain task priority + +**CALLING SEQUENCE:** + +.. code:: c + + rtems_status_code rtems_task_set_priority( + rtems_id id, + rtems_task_priority new_priority, + rtems_task_priority \*old_priority + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - task priority set successfully +``RTEMS_INVALID_ID`` - invalid task id +``RTEMS_INVALID_ADDRESS`` - invalid return argument pointer +``RTEMS_INVALID_PRIORITY`` - invalid task priority + +**DESCRIPTION:** + +This directive manipulates the priority of the task specified by +id. An id of ``RTEMS_SELF`` is used to indicate +the calling task. When new_priority is not equal to``RTEMS_CURRENT_PRIORITY``, the specified +task’s previous priority is returned in old_priority. When +new_priority is ``RTEMS_CURRENT_PRIORITY``, +the specified task’s current +priority is returned in old_priority. Valid priorities range +from a high of 1 to a low of 255. + +**NOTES:** + +The calling task may be preempted if its preemption mode is +enabled and it lowers its own priority or raises another task’s +priority. + +In case the new priority equals the current priority of the task, then nothing +happens. + +Setting the priority of a global task which does not reside on +the local node will generate a request to the remote node to +change the priority of the specified task. + +If the task specified by id is currently holding any binary +semaphores which use the priority inheritance algorithm, then +the task’s priority cannot be lowered immediately. If the +task’s priority were lowered immediately, then priority +inversion results. The requested lowering of the task’s +priority will occur when the task has released all priority +inheritance binary semaphores. The task’s priority can be +increased regardless of the task’s use of priority inheritance +binary semaphores. + +TASK_MODE - Change the current task mode +---------------------------------------- +.. index:: current task mode +.. index:: set task mode +.. index:: get task mode +.. index:: set task preemption mode +.. index:: get task preemption mode +.. index:: obtain task mode + +**CALLING SEQUENCE:** + +.. index:: rtems_task_mode + +.. code:: c + + rtems_status_code rtems_task_mode( + rtems_mode mode_set, + rtems_mode mask, + rtems_mode \*previous_mode_set + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - task mode set successfully +``RTEMS_INVALID_ADDRESS`` - ``previous_mode_set`` is NULL + +**DESCRIPTION:** + +This directive manipulates the execution mode of the calling +task. A task’s execution mode enables and disables preemption, +timeslicing, asynchronous signal processing, as well as +specifying the current interrupt level. To modify an execution +mode, the mode class(es) to be changed must be specified in the +mask parameter and the desired mode(s) must be specified in the +mode parameter. + +**NOTES:** + +The calling task will be preempted if it enables preemption and +a higher priority task is ready to run. + +Enabling timeslicing has no effect if preemption is disabled. For +a task to be timesliced, that task must have both preemption and +timeslicing enabled. + +A task can obtain its current execution mode, without modifying +it, by calling this directive with a mask value of``RTEMS_CURRENT_MODE``. + +To temporarily disable the processing of a valid ASR, a task +should call this directive with the ``RTEMS_NO_ASR`` +indicator specified in mode. + +The set of task mode constants and each mode’s corresponding +mask constant is provided in the following table: + +- ``RTEMS_PREEMPT`` is masked by``RTEMS_PREEMPT_MASK`` and enables preemption + +- ``RTEMS_NO_PREEMPT`` is masked by``RTEMS_PREEMPT_MASK`` and disables preemption + +- ``RTEMS_NO_TIMESLICE`` is masked by``RTEMS_TIMESLICE_MASK`` and disables timeslicing + +- ``RTEMS_TIMESLICE`` is masked by``RTEMS_TIMESLICE_MASK`` and enables timeslicing + +- ``RTEMS_ASR`` is masked by``RTEMS_ASR_MASK`` and enables ASR processing + +- ``RTEMS_NO_ASR`` is masked by``RTEMS_ASR_MASK`` and disables ASR processing + +- ``RTEMS_INTERRUPT_LEVEL(0)`` is masked by``RTEMS_INTERRUPT_MASK`` and enables all interrupts + +- ``RTEMS_INTERRUPT_LEVEL(n)`` is masked by``RTEMS_INTERRUPT_MASK`` and sets interrupts level n + +TASK_WAKE_AFTER - Wake up after interval +---------------------------------------- +.. index:: delay a task for an interval +.. index:: wake up after an interval + +**CALLING SEQUENCE:** + +.. index:: rtems_task_wake_after + +.. code:: c + + rtems_status_code rtems_task_wake_after( + rtems_interval ticks + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - always successful + +**DESCRIPTION:** + +This directive blocks the calling task for the specified number +of system clock ticks. When the requested interval has elapsed, +the task is made ready. The ``rtems_clock_tick`` +directive automatically updates the delay period. + +**NOTES:** + +Setting the system date and time with the``rtems_clock_set`` directive +has no effect on a ``rtems_task_wake_after`` blocked task. + +A task may give up the processor and remain in the ready state +by specifying a value of ``RTEMS_YIELD_PROCESSOR`` in ticks. + +The maximum timer interval that can be specified is the maximum +value which can be represented by the uint32_t type. + +A clock tick is required to support the functionality of this directive. + +TASK_WAKE_WHEN - Wake up when specified +--------------------------------------- +.. index:: delay a task until a wall time +.. index:: wake up at a wall time + +**CALLING SEQUENCE:** + +.. index:: rtems_task_wake_when + +.. code:: c + + rtems_status_code rtems_task_wake_when( + rtems_time_of_day \*time_buffer + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - awakened at date/time successfully +``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL +``RTEMS_INVALID_TIME_OF_DAY`` - invalid time buffer +``RTEMS_NOT_DEFINED`` - system date and time is not set + +**DESCRIPTION:** + +This directive blocks a task until the date and time specified +in time_buffer. At the requested date and time, the calling +task will be unblocked and made ready to execute. + +**NOTES:** + +The ticks portion of time_buffer structure is ignored. The +timing granularity of this directive is a second. + +A clock tick is required to support the functionality of this directive. + +ITERATE_OVER_ALL_THREADS - Iterate Over Tasks +--------------------------------------------- +.. index:: iterate over all threads + +**CALLING SEQUENCE:** + +.. index:: rtems_iterate_over_all_threads + +.. code:: c + + typedef void (\*rtems_per_thread_routine)( + Thread_Control \*the_thread + ); + void rtems_iterate_over_all_threads( + rtems_per_thread_routine routine + ); + +**DIRECTIVE STATUS CODES: NONE** + +**DESCRIPTION:** + +This directive iterates over all of the existant threads in the +system and invokes ``routine`` on each of them. The user should +be careful in accessing the contents of ``the_thread``. + +This routine is intended for use in diagnostic utilities and is +not intented for routine use in an operational system. + +**NOTES:** + +There is NO protection while this routine is called. Thus it is +possible that ``the_thread`` could be deleted while this is operating. +By not having protection, the user is free to invoke support routines +from the C Library which require semaphores for data structures. + +TASK_VARIABLE_ADD - Associate per task variable +----------------------------------------------- +.. index:: per-task variable +.. index:: task private variable +.. index:: task private data + +**CALLING SEQUENCE:** + +.. index:: rtems_task_variable_add + +.. code:: c + + rtems_status_code rtems_task_variable_add( + rtems_id tid, + void \**task_variable, + void (\*dtor)(void \*) + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - per task variable added successfully +``RTEMS_INVALID_ADDRESS`` - ``task_variable`` is NULL +``RTEMS_INVALID_ID`` - invalid task id +``RTEMS_NO_MEMORY`` - invalid task id +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - not supported on remote tasks + +**DESCRIPTION:** + +This directive adds the memory location specified by the +ptr argument to the context of the given task. The variable will +then be private to the task. The task can access and modify the +variable, but the modifications will not appear to other tasks, and +other tasks’ modifications to that variable will not affect the value +seen by the task. This is accomplished by saving and restoring the +variable’s value each time a task switch occurs to or from the calling task. +If the dtor argument is non-NULL it specifies the address of a ‘destructor’ +function which will be called when the task is deleted. The argument +passed to the destructor function is the task’s value of the variable. + +**NOTES:** + +This directive is deprecated and task variables will be removed. + +Task variables increase the context switch time to and from the +tasks that own them so it is desirable to minimize the number of +task variables. One efficient method +is to have a single task variable that is a pointer to a dynamically +allocated structure containing the task’s private ‘global’ data. +In this case the destructor function could be ‘free’. + +Per-task variables are disabled in SMP configurations and this service +is not available. + +TASK_VARIABLE_GET - Obtain value of a per task variable +------------------------------------------------------- +.. index:: get per-task variable +.. index:: obtain per-task variable + +**CALLING SEQUENCE:** + +.. index:: rtems_task_variable_get + +.. code:: c + + rtems_status_code rtems_task_variable_get( + rtems_id tid, + void \**task_variable, + void \**task_variable_value + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - per task variable obtained successfully +``RTEMS_INVALID_ADDRESS`` - ``task_variable`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``task_variable_value`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``task_variable`` is not found +``RTEMS_NO_MEMORY`` - invalid task id +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - not supported on remote tasks + +**DESCRIPTION:** + +This directive looks up the private value of a task variable for a +specified task and stores that value in the location pointed to by +the result argument. The specified task is usually not the calling +task, which can get its private value by directly accessing the variable. + +**NOTES:** + +This directive is deprecated and task variables will be removed. + +If you change memory which ``task_variable_value`` points to, +remember to declare that memory as volatile, so that the compiler +will optimize it correctly. In this case both the pointer``task_variable_value`` and data referenced by ``task_variable_value`` +should be considered volatile. + +Per-task variables are disabled in SMP configurations and this service +is not available. + +TASK_VARIABLE_DELETE - Remove per task variable +----------------------------------------------- +.. index:: per-task variable +.. index:: task private variable +.. index:: task private data + +**CALLING SEQUENCE:** + +.. index:: rtems_task_variable_delete + +.. code:: c + + rtems_status_code rtems_task_variable_delete( + rtems_id id, + void \**task_variable + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - per task variable deleted successfully +``RTEMS_INVALID_ID`` - invalid task id +``RTEMS_NO_MEMORY`` - invalid task id +``RTEMS_INVALID_ADDRESS`` - ``task_variable`` is NULL +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - not supported on remote tasks + +**DESCRIPTION:** + +This directive removes the given location from a task’s context. + +**NOTES:** + +This directive is deprecated and task variables will be removed. + +Per-task variables are disabled in SMP configurations and this service +is not available. + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Interrupt Manager +################# + +Introduction +============ + +Any real-time executive must provide a mechanism for +quick response to externally generated interrupts to satisfy the +critical time constraints of the application. The interrupt +manager provides this mechanism for RTEMS. This manager permits +quick interrupt response times by providing the critical ability +to alter task execution which allows a task to be preempted upon +exit from an ISR. The interrupt manager includes the following +directive: + +- ``rtems_interrupt_catch`` - Establish an ISR + +- ``rtems_interrupt_disable`` - Disable Interrupts + +- ``rtems_interrupt_enable`` - Enable Interrupts + +- ``rtems_interrupt_flash`` - Flash Interrupt + +- ``rtems_interrupt_local_disable`` - Disable Interrupts on Current Processor + +- ``rtems_interrupt_local_enable`` - Enable Interrupts on Current Processor + +- ``rtems_interrupt_lock_initialize`` - Initialize an ISR Lock + +- ``rtems_interrupt_lock_acquire`` - Acquire an ISR Lock + +- ``rtems_interrupt_lock_release`` - Release an ISR Lock + +- ``rtems_interrupt_lock_acquire_isr`` - Acquire an ISR Lock from ISR + +- ``rtems_interrupt_lock_release_isr`` - Release an ISR Lock from ISR + +- ``rtems_interrupt_is_in_progress`` - Is an ISR in Progress + +Background +========== + +Processing an Interrupt +----------------------- +.. index:: interrupt processing + +The interrupt manager allows the application to +connect a function to a hardware interrupt vector. When an +interrupt occurs, the processor will automatically vector to +RTEMS. RTEMS saves and restores all registers which are not +preserved by the normal C calling convention +for the target +processor and invokes the user’s ISR. The user’s ISR is +responsible for processing the interrupt, clearing the interrupt +if necessary, and device specific manipulation... index:: rtems_vector_number + +The ``rtems_interrupt_catch`` +directive connects a procedure to +an interrupt vector. The vector number is managed using +the ``rtems_vector_number`` data type. + +The interrupt service routine is assumed +to abide by these conventions and have a prototype similar to +the following:.. index:: rtems_isr + +.. code:: c + + rtems_isr user_isr( + rtems_vector_number vector + ); + +The vector number argument is provided by RTEMS to +allow the application to identify the interrupt source. This +could be used to allow a single routine to service interrupts +from multiple instances of the same device. For example, a +single routine could service interrupts from multiple serial +ports and use the vector number to identify which port requires +servicing. + +To minimize the masking of lower or equal priority +level interrupts, the ISR should perform the minimum actions +required to service the interrupt. Other non-essential actions +should be handled by application tasks. Once the user’s ISR has +completed, it returns control to the RTEMS interrupt manager +which will perform task dispatching and restore the registers +saved before the ISR was invoked. + +The RTEMS interrupt manager guarantees that proper +task scheduling and dispatching are performed at the conclusion +of an ISR. A system call made by the ISR may have readied a +task of higher priority than the interrupted task. Therefore, +when the ISR completes, the postponed dispatch processing must +be performed. No dispatch processing is performed as part of +directives which have been invoked by an ISR. + +Applications must adhere to the following rule if +proper task scheduling and dispatching is to be performed: + +- ** *The interrupt manager must be used for all ISRs which + may be interrupted by the highest priority ISR which invokes an + RTEMS directive.* + +Consider a processor which allows a numerically low +interrupt level to interrupt a numerically greater interrupt +level. In this example, if an RTEMS directive is used in a +level 4 ISR, then all ISRs which execute at levels 0 through 4 +must use the interrupt manager. + +Interrupts are nested whenever an interrupt occurs +during the execution of another ISR. RTEMS supports efficient +interrupt nesting by allowing the nested ISRs to terminate +without performing any dispatch processing. Only when the +outermost ISR terminates will the postponed dispatching occur. + +RTEMS Interrupt Levels +---------------------- +.. index:: interrupt levels + +Many processors support multiple interrupt levels or +priorities. The exact number of interrupt levels is processor +dependent. RTEMS internally supports 256 interrupt levels which +are mapped to the processor’s interrupt levels. For specific +information on the mapping between RTEMS and the target +processor’s interrupt levels, refer to the Interrupt Processing +chapter of the Applications Supplement document for a specific +target processor. + +Disabling of Interrupts by RTEMS +-------------------------------- +.. index:: disabling interrupts + +During the execution of directive calls, critical +sections of code may be executed. When these sections are +encountered, RTEMS disables all maskable interrupts before the +execution of the section and restores them to the previous level +upon completion of the section. RTEMS has been optimized to +ensure that interrupts are disabled for a minimum length of +time. The maximum length of time interrupts are disabled by +RTEMS is processor dependent and is detailed in the Timing +Specification chapter of the Applications Supplement document +for a specific target processor. + +Non-maskable interrupts (NMI) cannot be disabled, and +ISRs which execute at this level MUST NEVER issue RTEMS system +calls. If a directive is invoked, unpredictable results may +occur due to the inability of RTEMS to protect its critical +sections. However, ISRs that make no system calls may safely +execute as non-maskable interrupts. + +Operations +========== + +Establishing an ISR +------------------- + +The ``rtems_interrupt_catch`` +directive establishes an ISR for +the system. The address of the ISR and its associated CPU +vector number are specified to this directive. This directive +installs the RTEMS interrupt wrapper in the processor’s +Interrupt Vector Table and the address of the user’s ISR in the +RTEMS’ Vector Table. This directive returns the previous +contents of the specified vector in the RTEMS’ Vector Table. + +Directives Allowed from an ISR +------------------------------ + +Using the interrupt manager ensures that RTEMS knows +when a directive is being called from an ISR. The ISR may then +use system calls to synchronize itself with an application task. +The synchronization may involve messages, events or signals +being passed by the ISR to the desired task. Directives invoked +by an ISR must operate only on objects which reside on the local +node. The following is a list of RTEMS system calls that may be +made from an ISR: + +- Task Management + Although it is acceptable to operate on the RTEMS_SELF task (e.g. + the currently executing task), while in an ISR, this will refer + to the interrupted task. Most of the time, it is an application + implementation error to use RTEMS_SELF from an ISR. + - rtems_task_suspend + - rtems_task_resume + +- Interrupt Management + - rtems_interrupt_enable + - rtems_interrupt_disable + - rtems_interrupt_flash + - rtems_interrupt_lock_acquire + - rtems_interrupt_lock_release + - rtems_interrupt_lock_acquire_isr + - rtems_interrupt_lock_release_isr + - rtems_interrupt_is_in_progress + - rtems_interrupt_catch + +- Clock Management + - rtems_clock_set + - rtems_clock_get + - rtems_clock_get_tod + - rtems_clock_get_tod_timeval + - rtems_clock_get_seconds_since_epoch + - rtems_clock_get_ticks_per_second + - rtems_clock_get_ticks_since_boot + - rtems_clock_get_uptime + - rtems_clock_set_nanoseconds_extension + - rtems_clock_tick + +- Timer Management + - rtems_timer_cancel + - rtems_timer_reset + - rtems_timer_fire_after + - rtems_timer_fire_when + - rtems_timer_server_fire_after + - rtems_timer_server_fire_when + +- Event Management + - rtems_event_send + - rtems_event_system_send + - rtems_event_transient_send + +- Semaphore Management + - rtems_semaphore_release + +- Message Management + - rtems_message_queue_send + - rtems_message_queue_urgent + +- Signal Management + - rtems_signal_send + +- Dual-Ported Memory Management + - rtems_port_external_to_internal + - rtems_port_internal_to_external + +- IO Management + The following services are safe to call from an ISR if and only if + the device driver service invoked is also safe. The IO Manager itself + is safe but the invoked driver entry point may or may not be. + - rtems_io_initialize + - rtems_io_open + - rtems_io_close + - rtems_io_read + - rtems_io_write + - rtems_io_control + +- Fatal Error Management + - rtems_fatal + - rtems_fatal_error_occurred + +- Multiprocessing + - rtems_multiprocessing_announce + +Directives +========== + +This section details the interrupt manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +INTERRUPT_CATCH - Establish an ISR +---------------------------------- +.. index:: establish an ISR +.. index:: install an ISR + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_catch + +.. code:: c + + rtems_status_code rtems_interrupt_catch( + rtems_isr_entry new_isr_handler, + rtems_vector_number vector, + rtems_isr_entry \*old_isr_handler + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - ISR established successfully +``RTEMS_INVALID_NUMBER`` - illegal vector number +``RTEMS_INVALID_ADDRESS`` - illegal ISR entry point or invalid ``old_isr_handler`` + +**DESCRIPTION:** + +This directive establishes an interrupt service +routine (ISR) for the specified interrupt vector number. The``new_isr_handler`` parameter specifies the entry point of the ISR. +The entry point of the previous ISR for the specified vector is +returned in ``old_isr_handler``. + +To release an interrupt vector, pass the old handler’s address obtained +when the vector was first capture. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +INTERRUPT_DISABLE - Disable Interrupts +-------------------------------------- +.. index:: disable interrupts + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_disable + +.. code:: c + + void rtems_interrupt_disable( + rtems_interrupt_level level + ); + /* this is implemented as a macro and sets level as a side-effect \*/ + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive disables all maskable interrupts and returns +the previous ``level``. A later invocation of the``rtems_interrupt_enable`` directive should be used to +restore the interrupt level. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +*This directive is implemented as a macro which modifies the ``level`` +parameter.* + +This directive is only available on uni-processor configurations. The +directive ``rtems_interrupt_local_disable`` is available on all +configurations. + +INTERRUPT_ENABLE - Enable Interrupts +------------------------------------ +.. index:: enable interrupts + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_enable + +.. code:: c + + void rtems_interrupt_enable( + rtems_interrupt_level level + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive enables maskable interrupts to the ``level`` +which was returned by a previous call to``rtems_interrupt_disable``. +Immediately prior to invoking this directive, maskable interrupts should +be disabled by a call to ``rtems_interrupt_disable`` +and will be enabled when this directive returns to the caller. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +This directive is only available on uni-processor configurations. The +directive ``rtems_interrupt_local_enable`` is available on all +configurations. + +INTERRUPT_FLASH - Flash Interrupts +---------------------------------- +.. index:: flash interrupts + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_flash + +.. code:: c + + void rtems_interrupt_flash( + rtems_interrupt_level level + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive temporarily enables maskable interrupts to the ``level`` +which was returned by a previous call to``rtems_interrupt_disable``. +Immediately prior to invoking this directive, maskable interrupts should +be disabled by a call to ``rtems_interrupt_disable`` +and will be redisabled when this directive returns to the caller. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +This directive is only available on uni-processor configurations. The +directives ``rtems_interrupt_local_disable`` and``rtems_interrupt_local_enable`` is available on all +configurations. + +INTERRUPT_LOCAL_DISABLE - Disable Interrupts on Current Processor +----------------------------------------------------------------- +.. index:: disable interrupts + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_local_disable + +.. code:: c + + void rtems_interrupt_local_disable( + rtems_interrupt_level level + ); + /* this is implemented as a macro and sets level as a side-effect \*/ + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive disables all maskable interrupts and returns +the previous ``level``. A later invocation of the``rtems_interrupt_local_enable`` directive should be used to +restore the interrupt level. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +*This directive is implemented as a macro which modifies the ``level`` +parameter.* + +On SMP configurations this will not ensure system wide mutual exclusion. Use +interrupt locks instead. + +INTERRUPT_LOCAL_ENABLE - Enable Interrupts on Current Processor +--------------------------------------------------------------- +.. index:: enable interrupts + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_local_enable + +.. code:: c + + void rtems_interrupt_local_enable( + rtems_interrupt_level level + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive enables maskable interrupts to the ``level`` +which was returned by a previous call to``rtems_interrupt_local_disable``. +Immediately prior to invoking this directive, maskable interrupts should +be disabled by a call to ``rtems_interrupt_local_disable`` +and will be enabled when this directive returns to the caller. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +INTERRUPT_LOCK_INITIALIZE - Initialize an ISR Lock +-------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_lock_initialize + +.. code:: c + + void rtems_interrupt_lock_initialize( + rtems_interrupt_lock \*lock + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +Initializes an interrupt lock. + +**NOTES:** + +Concurrent initialization leads to unpredictable results. + +INTERRUPT_LOCK_ACQUIRE - Acquire an ISR Lock +-------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_lock_acquire + +.. code:: c + + void rtems_interrupt_lock_acquire( + rtems_interrupt_lock \*lock, + rtems_interrupt_level level + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +Interrupts will be disabled. On SMP configurations this directive acquires a +SMP lock. + +**NOTES:** + +This directive will not cause the calling thread to be preempted. This +directive can be used in thread and interrupt context. + +INTERRUPT_LOCK_RELEASE - Release an ISR Lock +-------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_lock_release + +.. code:: c + + void rtems_interrupt_lock_release( + rtems_interrupt_lock \*lock, + rtems_interrupt_level level + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +The interrupt status will be restored. On SMP configurations this directive +releases a SMP lock. + +**NOTES:** + +This directive will not cause the calling thread to be preempted. This +directive can be used in thread and interrupt context. + +INTERRUPT_LOCK_ACQUIRE_ISR - Acquire an ISR Lock from ISR +--------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_lock_acquire_isr + +.. code:: c + + void rtems_interrupt_lock_acquire_isr( + rtems_interrupt_lock \*lock, + rtems_interrupt_level level + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +The interrupt status will remain unchanged. On SMP configurations this +directive acquires a SMP lock. + +In case the corresponding interrupt service routine can be interrupted by +higher priority interrupts and these interrupts enter the critical section +protected by this lock, then the result is unpredictable. + +**NOTES:** + +This directive should be called from the corresponding interrupt service +routine. + +INTERRUPT_LOCK_RELEASE_ISR - Release an ISR Lock from ISR +--------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_lock_release_isr + +.. code:: c + + void rtems_interrupt_lock_release_isr( + rtems_interrupt_lock \*lock, + rtems_interrupt_level level + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +The interrupt status will remain unchanged. On SMP configurations this +directive releases a SMP lock. + +**NOTES:** + +This directive should be called from the corresponding interrupt service +routine. + +INTERRUPT_IS_IN_PROGRESS - Is an ISR in Progress +------------------------------------------------ +.. index:: is interrupt in progress + +**CALLING SEQUENCE:** + +.. index:: rtems_interrupt_is_in_progress + +.. code:: c + + bool rtems_interrupt_is_in_progress( void ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive returns ``TRUE`` if the processor is currently +servicing an interrupt and ``FALSE`` otherwise. A return value +of ``TRUE`` indicates that the caller is an interrupt service +routine, *NOT* a task. The directives available to an interrupt +service routine are restricted. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +.. COMMENT: COPYRIGHT (c) 1988-2008 + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Clock Manager +############# + +.. index:: clock + +Introduction +============ + +The clock manager provides support for time of day +and other time related capabilities. The directives provided by +the clock manager are: + +- ``rtems_clock_set`` - Set date and time + +- ``rtems_clock_get`` - Get date and time information + +- ``rtems_clock_get_tod`` - Get date and time in TOD format + +- ``rtems_clock_get_tod_timeval`` - Get date and time in timeval format + +- ``rtems_clock_get_seconds_since_epoch`` - Get seconds since epoch + +- ``rtems_clock_get_ticks_per_second`` - Get ticks per second + +- ``rtems_clock_get_ticks_since_boot`` - Get current ticks counter value + +- ``rtems_clock_tick_later`` - Get tick value in the future + +- ``rtems_clock_tick_later_usec`` - Get tick value in the future in microseconds + +- ``rtems_clock_tick_before`` - Is tick value is before a point in time + +- ``rtems_clock_get_uptime`` - Get time since boot + +- ``rtems_clock_get_uptime_timeval`` - Get time since boot in timeval format + +- ``rtems_clock_get_uptime_seconds`` - Get seconds since boot + +- ``rtems_clock_get_uptime_nanoseconds`` - Get nanoseconds since boot + +- ``rtems_clock_set_nanoseconds_extension`` - Install the nanoseconds since last tick handler + +- ``rtems_clock_tick`` - Announce a clock tick + +Background +========== + +Required Support +---------------- + +For the features provided by the clock manager to be +utilized, periodic timer interrupts are required. Therefore, a +real-time clock or hardware timer is necessary to create the +timer interrupts. The ``rtems_clock_tick`` +directive is normally called +by the timer ISR to announce to RTEMS that a system clock tick +has occurred. Elapsed time is measured in ticks. A tick is +defined to be an integral number of microseconds which is +specified by the user in the Configuration Table. + + +Time and Date Data Structures +----------------------------- + +The clock facilities of the clock manager operate +upon calendar time. These directives utilize the following date +and time structure for the native time and date format: +.. index:: rtems_time_of_day + +.. code:: c + + struct rtems_tod_control { + uint32_t year; /* greater than 1987 \*/ + uint32_t month; /* 1 - 12 \*/ + uint32_t day; /* 1 - 31 \*/ + uint32_t hour; /* 0 - 23 \*/ + uint32_t minute; /* 0 - 59 \*/ + uint32_t second; /* 0 - 59 \*/ + uint32_t ticks; /* elapsed between seconds \*/ + }; + typedef struct rtems_tod_control rtems_time_of_day; + +The native date and time format is the only format +supported when setting the system date and time using the``rtems_clock_set`` directive. Some applications +expect to operate on a "UNIX-style" date and time data structure. The``rtems_clock_get_tod_timeval`` always returns +the date and time in ``struct timeval`` format. The``rtems_clock_get`` directive can optionally return +the current date and time in this format. + +The ``struct timeval`` data structure has two fields: ``tv_sec`` +and ``tv_usec`` which are seconds and microseconds, respectively. +The ``tv_sec`` field in this data structure is the number of seconds +since the POSIX epoch of January 1, 1970 but will never be prior to +the RTEMS epoch of January 1, 1988. + +Clock Tick and Timeslicing +-------------------------- +.. index:: timeslicing + +Timeslicing is a task scheduling discipline in which +tasks of equal priority are executed for a specific period of +time before control of the CPU is passed to another task. It is +also sometimes referred to as the automatic round-robin +scheduling algorithm. The length of time allocated to each task +is known as the quantum or timeslice. + +The system’s timeslice is defined as an integral +number of ticks, and is specified in the Configuration Table. +The timeslice is defined for the entire system of tasks, but +timeslicing is enabled and disabled on a per task basis. + +The ``rtems_clock_tick`` +directive implements timeslicing by +decrementing the running task’s time-remaining counter when both +timeslicing and preemption are enabled. If the task’s timeslice +has expired, then that task will be preempted if there exists a +ready task of equal priority. + +Delays +------ +.. index:: delays + +A sleep timer allows a task to delay for a given +interval or up until a given time, and then wake and continue +execution. This type of timer is created automatically by the``rtems_task_wake_after`` +and ``rtems_task_wake_when`` directives and, as a result, +does not have an RTEMS ID. Once activated, a sleep timer cannot +be explicitly deleted. Each task may activate one and only one +sleep timer at a time. + +Timeouts +-------- +.. index:: timeouts + +Timeouts are a special type of timer automatically +created when the timeout option is used on the``rtems_message_queue_receive``,``rtems_event_receive``,``rtems_semaphore_obtain`` and``rtems_region_get_segment`` directives. +Each task may have one and only one timeout active at a time. +When a timeout expires, it unblocks the task with a timeout status code. + +Operations +========== + +Announcing a Tick +----------------- + +RTEMS provides the ``rtems_clock_tick`` directive which is +called from the user’s real-time clock ISR to inform RTEMS that +a tick has elapsed. The tick frequency value, defined in +microseconds, is a configuration parameter found in the +Configuration Table. RTEMS divides one million microseconds +(one second) by the number of microseconds per tick to determine +the number of calls to the``rtems_clock_tick`` directive per second. The +frequency of ``rtems_clock_tick`` +calls determines the resolution +(granularity) for all time dependent RTEMS actions. For +example, calling ``rtems_clock_tick`` +ten times per second yields a higher +resolution than calling ``rtems_clock_tick`` +two times per second. The ``rtems_clock_tick`` +directive is responsible for maintaining both +calendar time and the dynamic set of timers. + +Setting the Time +---------------- + +The ``rtems_clock_set`` directive allows a task or an ISR to +set the date and time maintained by RTEMS. If setting the date +and time causes any outstanding timers to pass their deadline, +then the expired timers will be fired during the invocation of +the ``rtems_clock_set`` directive. + +Obtaining the Time +------------------ + +The ``rtems_clock_get`` directive allows a task or an ISR to +obtain the current date and time or date and time related +information. The current date and time can be returned in +either native or UNIX-style format. Additionally, the +application can obtain date and time related information such as +the number of seconds since the RTEMS epoch, the number of ticks +since the executive was initialized, and the number of ticks per +second. The information returned by the``rtems_clock_get`` directive is +dependent on the option selected by the caller. This +is specified using one of the following constants +associated with the enumerated type``rtems_clock_get_options``:.. index:: rtems_clock_get_options + +- ``RTEMS_CLOCK_GET_TOD`` - obtain native style date and time + +- ``RTEMS_CLOCK_GET_TIME_VALUE`` - obtain UNIX-style + date and time + +- ``RTEMS_CLOCK_GET_TICKS_SINCE_BOOT`` - obtain number of ticks + since RTEMS was initialized + +- ``RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH`` - obtain number + of seconds since RTEMS epoch + +- ``RTEMS_CLOCK_GET_TICKS_PER_SECOND`` - obtain number of clock + ticks per second + +Calendar time operations will return an error code if +invoked before the date and time have been set. + +Directives +========== + +This section details the clock manager’s directives. +A subsection is dedicated to each of this manager’s directives +and describes the calling sequence, related constants, usage, +and status codes. + +CLOCK_SET - Set date and time +----------------------------- + +**CALLING SEQUENCE:** + +.. index:: set the time of day + +.. index:: rtems_clock_set + +.. code:: c + + rtems_status_code rtems_clock_set( + rtems_time_of_day \*time_buffer + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - date and time set successfully +``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL +``RTEMS_INVALID_CLOCK`` - invalid time of day + +**DESCRIPTION:** + +This directive sets the system date and time. The +date, time, and ticks in the time_buffer structure are all +range-checked, and an error is returned if any one is out of its +valid range. + +**NOTES:** + +Years before 1988 are invalid. + +The system date and time are based on the configured +tick rate (number of microseconds in a tick). + +Setting the time forward may cause a higher priority +task, blocked waiting on a specific time, to be made ready. In +this case, the calling task will be preempted after the next +clock tick. + +Re-initializing RTEMS causes the system date and time +to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize +the system date and time to application specific specifications. + +CLOCK_GET - Get date and time information +----------------------------------------- +.. index:: obtain the time of day + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get + +.. code:: c + + rtems_status_code rtems_clock_get( + rtems_clock_get_options option, + void \*time_buffer + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - current time obtained successfully +``RTEMS_NOT_DEFINED`` - system date and time is not set +``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL + +**DESCRIPTION:** + +This directive is deprecated. + +This directive obtains the system date and time. If +the caller is attempting to obtain the date and time (i.e. +option is set to either ``RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH``,``RTEMS_CLOCK_GET_TOD``, or``RTEMS_CLOCK_GET_TIME_VALUE``) and the date and time +has not been set with a previous call to``rtems_clock_set``, then the``RTEMS_NOT_DEFINED`` status code is returned. +The caller can always obtain the number of ticks per second (option is``RTEMS_CLOCK_GET_TICKS_PER_SECOND``) and the number of +ticks since the executive was initialized option is``RTEMS_CLOCK_GET_TICKS_SINCE_BOOT``). + +The ``option`` argument may taken on any value of the enumerated +type ``rtems_clock_get_options``. The data type expected for``time_buffer`` is based on the value of ``option`` as +indicated below:.. index:: rtems_clock_get_options + +- ``RTEMS_CLOCK_GET_TOD`` - (rtems_time_of_day \*) + +- ``RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH`` - (rtems_interval \*) + +- ``RTEMS_CLOCK_GET_TICKS_SINCE_BOOT`` - (rtems_interval \*) + +- ``RTEMS_CLOCK_GET_TICKS_PER_SECOND`` - (rtems_interval \*) + +- ``RTEMS_CLOCK_GET_TIME_VALUE`` - (struct timeval \*) + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the running task to be +preempted. Re-initializing RTEMS causes the system date and +time to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize the +system date and time to application specific specifications. + +CLOCK_GET_TOD - Get date and time in TOD format +----------------------------------------------- +.. index:: obtain the time of day + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get_tod + +.. code:: c + + rtems_status_code rtems_clock_get_tod( + rtems_time_of_day \*time_buffer + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - current time obtained successfully +``RTEMS_NOT_DEFINED`` - system date and time is not set +``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL + +**DESCRIPTION:** + +This directive obtains the system date and time. If the date and time +has not been set with a previous call to``rtems_clock_set``, then the``RTEMS_NOT_DEFINED`` status code is returned. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the running task to be +preempted. Re-initializing RTEMS causes the system date and +time to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize the +system date and time to application specific specifications. + +CLOCK_GET_TOD_TIMEVAL - Get date and time in timeval format +----------------------------------------------------------- +.. index:: obtain the time of day + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get_tod_timeval + +.. code:: c + + rtems_status_code rtems_clock_get_tod( + struct timeval \*time + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - current time obtained successfully +``RTEMS_NOT_DEFINED`` - system date and time is not set +``RTEMS_INVALID_ADDRESS`` - ``time`` is NULL + +**DESCRIPTION:** + +This directive obtains the system date and time in POSIX``struct timeval`` format. If the date and time +has not been set with a previous call to``rtems_clock_set``, then the``RTEMS_NOT_DEFINED`` status code is returned. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the running task to be +preempted. Re-initializing RTEMS causes the system date and +time to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize the +system date and time to application specific specifications. + +CLOCK_GET_SECONDS_SINCE_EPOCH - Get seconds since epoch +------------------------------------------------------- +.. index:: obtain seconds since epoch + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get_seconds_since_epoch + +.. code:: c + + rtems_status_code rtems_clock_get_seconds_since_epoch( + rtems_interval \*the_interval + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - current time obtained successfully +``RTEMS_NOT_DEFINED`` - system date and time is not set +``RTEMS_INVALID_ADDRESS`` - ``the_interval`` is NULL + +**DESCRIPTION:** + +This directive returns the number of seconds since the RTEMS +epoch and the current system date and time. If the date and time +has not been set with a previous call to``rtems_clock_set``, then the``RTEMS_NOT_DEFINED`` status code is returned. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the running task to be +preempted. Re-initializing RTEMS causes the system date and +time to be reset to an uninitialized state. Another call to``rtems_clock_set`` is required to re-initialize the +system date and time to application specific specifications. + +CLOCK_GET_TICKS_PER_SECOND - Get ticks per second +------------------------------------------------- +.. index:: obtain seconds since epoch + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get_ticks_per_second + +.. code:: c + + rtems_interval rtems_clock_get_ticks_per_second(void); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive returns the number of clock ticks per second. This +is strictly based upon the microseconds per clock tick that the +application has configured. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the running task to be preempted. + +CLOCK_GET_TICKS_SINCE_BOOT - Get current ticks counter value +------------------------------------------------------------ +.. index:: obtain ticks since boot +.. index:: get current ticks counter value + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get_ticks_since_boot + +.. code:: c + + rtems_interval rtems_clock_get_ticks_since_boot(void); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive returns the current tick counter value. With a 1ms clock tick, +this counter overflows after 50 days since boot. This is the historical +measure of uptime in an RTEMS system. The newer service``rtems_clock_get_uptime`` is another and potentially more +accurate way of obtaining similar information. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the running task to be preempted. + +CLOCK_TICK_LATER - Get tick value in the future +----------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_tick_later + +.. code:: c + + rtems_interval rtems_clock_tick_later( + rtems_interval delta + ); + +**DESCRIPTION:** + +Returns the ticks counter value delta ticks in the future. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the running task to be preempted. + +CLOCK_TICK_LATER_USEC - Get tick value in the future in microseconds +-------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_tick_later_usec + +.. code:: c + + rtems_interval rtems_clock_tick_later_usec( + rtems_interval delta_in_usec + ); + +**DESCRIPTION:** + +Returns the ticks counter value at least delta microseconds in the future. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the running task to be preempted. + +CLOCK_TICK_BEFORE - Is tick value is before a point in time +----------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_tick_before + +.. code:: c + + rtems_interval rtems_clock_tick_before( + rtems_interval tick + ); + +**DESCRIPTION:** + +Returns true if the current ticks counter value indicates a time before the +time specified by the tick value and false otherwise. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the running task to be preempted. + +**EXAMPLE:** + +.. code:: c + + status busy( void ) + { + rtems_interval timeout = rtems_clock_tick_later_usec( 10000 ); + do { + if ( ok() ) { + return success; + } + } while ( rtems_clock_tick_before( timeout ) ); + return timeout; + } + +CLOCK_GET_UPTIME - Get the time since boot +------------------------------------------ +.. index:: clock get uptime +.. index:: uptime + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get_uptime + +.. code:: c + + rtems_status_code rtems_clock_get_uptime( + struct timespec \*uptime + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - clock tick processed successfully +``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL + +**DESCRIPTION:** + +This directive returns the seconds and nanoseconds since the +system was booted. If the BSP supports nanosecond clock +accuracy, the time reported will probably be different on every +call. + +**NOTES:** + +This directive may be called from an ISR. + +CLOCK_GET_UPTIME_TIMEVAL - Get the time since boot in timeval format +-------------------------------------------------------------------- +.. index:: clock get uptime +.. index:: uptime + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get_uptime_timeval + +.. code:: c + + void rtems_clock_get_uptime_timeval( + struct timeval \*uptime + ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive returns the seconds and microseconds since the +system was booted. If the BSP supports nanosecond clock +accuracy, the time reported will probably be different on every +call. + +**NOTES:** + +This directive may be called from an ISR. + +CLOCK_GET_UPTIME_SECONDS - Get the seconds since boot +----------------------------------------------------- +.. index:: clock get uptime +.. index:: uptime + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get_uptime_seconds + +.. code:: c + + time_t rtems_clock_get_uptime_seconds(void); + +**DIRECTIVE STATUS CODES:** + +The system uptime in seconds. + +**DESCRIPTION:** + +This directive returns the seconds since the system was booted. + +**NOTES:** + +This directive may be called from an ISR. + +CLOCK_GET_UPTIME_NANOSECONDS - Get the nanoseconds since boot +------------------------------------------------------------- +.. index:: clock get nanoseconds uptime +.. index:: uptime + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_get_uptime_nanoseconds + +.. code:: c + + uint64_t rtems_clock_get_uptime_nanoseconds(void); + +**DIRECTIVE STATUS CODES:** + +The system uptime in nanoseconds. + +**DESCRIPTION:** + +This directive returns the nanoseconds since the system was booted. + +**NOTES:** + +This directive may be called from an ISR. + +CLOCK_SET_NANOSECONDS_EXTENSION - Install the nanoseconds since last tick handler +--------------------------------------------------------------------------------- +.. index:: clock set nanoseconds extension +.. index:: nanoseconds extension +.. index:: nanoseconds time accuracy + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_set_nanoseconds_extension + +.. code:: c + + rtems_status_code rtems_clock_set_nanoseconds_extension( + rtems_nanoseconds_extension_routine routine + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - clock tick processed successfully +``RTEMS_INVALID_ADDRESS`` - ``time_buffer`` is NULL + +**DESCRIPTION:** + +This directive is used by the Clock device driver to install the``routine`` which will be invoked by the internal RTEMS method used to +obtain a highly accurate time of day. It is usually called during +the initialization of the driver. + +When the ``routine`` is invoked, it will determine the number of +nanoseconds which have elapsed since the last invocation of +the ``rtems_clock_tick`` directive. It should do +this as quickly as possible with as little impact as possible +on the device used as a clock source. + +**NOTES:** + +This directive may be called from an ISR. + +This directive is called as part of every service to obtain the +current date and time as well as timestamps. + +CLOCK_TICK - Announce a clock tick +---------------------------------- +.. index:: clock tick + +**CALLING SEQUENCE:** + +.. index:: rtems_clock_tick + +.. code:: c + + rtems_status_code rtems_clock_tick( void ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - clock tick processed successfully + +**DESCRIPTION:** + +This directive announces to RTEMS that a system clock +tick has occurred. The directive is usually called from the +timer interrupt ISR of the local processor. This directive +maintains the system date and time, decrements timers for +delayed tasks, timeouts, rate monotonic periods, and implements +timeslicing. + +**NOTES:** + +This directive is typically called from an ISR. + +The ``microseconds_per_tick`` and ``ticks_per_timeslice`` +parameters in the Configuration Table contain the number of +microseconds per tick and number of ticks per timeslice, +respectively. + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Timer Manager +############# + +.. index:: timers + +Introduction +============ + +The timer manager provides support for timer +facilities. The directives provided by the timer manager are: + +- ``rtems_timer_create`` - Create a timer + +- ``rtems_timer_ident`` - Get ID of a timer + +- ``rtems_timer_cancel`` - Cancel a timer + +- ``rtems_timer_delete`` - Delete a timer + +- ``rtems_timer_fire_after`` - Fire timer after interval + +- ``rtems_timer_fire_when`` - Fire timer when specified + +- ``rtems_timer_initiate_server`` - Initiate server for task-based timers + +- ``rtems_timer_server_fire_after`` - Fire task-based timer after interval + +- ``rtems_timer_server_fire_when`` - Fire task-based timer when specified + +- ``rtems_timer_reset`` - Reset an interval timer + +Background +========== + +Required Support +---------------- + +A clock tick is required to support the functionality provided by this manager. + +Timers +------ + +A timer is an RTEMS object which allows the +application to schedule operations to occur at specific times in +the future. User supplied timer service routines are invoked by +either the ``rtems_clock_tick`` directive or +a special Timer Server task when the timer fires. Timer service +routines may perform any operations or directives which normally +would be performed by the application code which invoked the``rtems_clock_tick`` directive. + +The timer can be used to implement watchdog routines +which only fire to denote that an application error has +occurred. The timer is reset at specific points in the +application to ensure that the watchdog does not fire. Thus, if +the application does not reset the watchdog timer, then the +timer service routine will fire to indicate that the application +has failed to reach a reset point. This use of a timer is +sometimes referred to as a "keep alive" or a "deadman" timer. + +Timer Server +------------ + +The Timer Server task is responsible for executing the timer +service routines associated with all task-based timers. +This task executes at a priority higher than any RTEMS application +task, and is created non-preemptible, and thus can be viewed logically as +the lowest priority interrupt. + +By providing a mechanism where timer service routines execute +in task rather than interrupt space, the application is +allowed a bit more flexibility in what operations a timer +service routine can perform. For example, the Timer Server +can be configured to have a floating point context in which case +it would be safe to perform floating point operations +from a task-based timer. Most of the time, executing floating +point instructions from an interrupt service routine +is not considered safe. However, since the Timer Server task +is non-preemptible, only directives allowed from an ISR can be +called in the timer service routine. + +The Timer Server is designed to remain blocked until a +task-based timer fires. This reduces the execution overhead +of the Timer Server. + +Timer Service Routines +---------------------- + +The timer service routine should adhere to C calling +conventions and have a prototype similar to the following:.. index:: rtems_timer_service_routine + +.. code:: c + + rtems_timer_service_routine user_routine( + rtems_id timer_id, + void \*user_data + ); + +Where the timer_id parameter is the RTEMS object ID +of the timer which is being fired and user_data is a pointer to +user-defined information which may be utilized by the timer +service routine. The argument user_data may be NULL. + +Operations +========== + +Creating a Timer +---------------- + +The ``rtems_timer_create`` directive creates a timer by +allocating a Timer Control Block (TMCB), assigning the timer a +user-specified name, and assigning it a timer ID. Newly created +timers do not have a timer service routine associated with them +and are not active. + +Obtaining Timer IDs +------------------- + +When a timer is created, RTEMS generates a unique +timer ID and assigns it to the created timer until it is +deleted. The timer ID may be obtained by either of two methods. +First, as the result of an invocation of the``rtems_timer_create`` +directive, the timer ID is stored in a user provided location. +Second, the timer ID may be obtained later using the``rtems_timer_ident`` directive. The timer ID +is used by other directives to manipulate this timer. + +Initiating an Interval Timer +---------------------------- + +The ``rtems_timer_fire_after`` +and ``rtems_timer_server_fire_after`` +directives initiate a timer to fire a user provided +timer service routine after the specified +number of clock ticks have elapsed. When the interval has +elapsed, the timer service routine will be invoked from the``rtems_clock_tick`` directive if it was initiated +by the ``rtems_timer_fire_after`` directive +and from the Timer Server task if initiated by the``rtems_timer_server_fire_after`` directive. + +Initiating a Time of Day Timer +------------------------------ + +The ``rtems_timer_fire_when`` +and ``rtems_timer_server_fire_when`` +directive initiate a timer to +fire a user provided timer service routine when the specified +time of day has been reached. When the interval has elapsed, +the timer service routine will be invoked from the``rtems_clock_tick`` directive +by the ``rtems_timer_fire_when`` directive +and from the Timer Server task if initiated by the``rtems_timer_server_fire_when`` directive. + +Canceling a Timer +----------------- + +The ``rtems_timer_cancel`` directive is used to halt the +specified timer. Once canceled, the timer service routine will +not fire unless the timer is reinitiated. The timer can be +reinitiated using the ``rtems_timer_reset``,``rtems_timer_fire_after``, and``rtems_timer_fire_when`` directives. + +Resetting a Timer +----------------- + +The ``rtems_timer_reset`` directive is used to restore an +interval timer initiated by a previous invocation of``rtems_timer_fire_after`` or``rtems_timer_server_fire_after`` to +its original interval length. If the +timer has not been used or the last usage of this timer +was by the ``rtems_timer_fire_when`` +or ``rtems_timer_server_fire_when`` +directive, then an error is returned. The timer service routine +is not changed or fired by this directive. + +Initiating the Timer Server +--------------------------- + +The ``rtems_timer_initiate_server`` directive is used to +allocate and start the execution of the Timer Server task. The +application can specify both the stack size and attributes of the +Timer Server. The Timer Server executes at a priority higher than +any application task and thus the user can expect to be preempted +as the result of executing the ``rtems_timer_initiate_server`` +directive. + +Deleting a Timer +---------------- + +The ``rtems_timer_delete`` directive is used to delete a timer. +If the timer is running and has not expired, the timer is +automatically canceled. The timer’s control block is returned +to the TMCB free list when it is deleted. A timer can be +deleted by a task other than the task which created the timer. +Any subsequent references to the timer’s name and ID are invalid. + +Directives +========== + +This section details the timer manager’s directives. +A subsection is dedicated to each of this manager’s directives +and describes the calling sequence, related constants, usage, +and status codes. + +TIMER_CREATE - Create a timer +----------------------------- +.. index:: create a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_create + +.. code:: c + + rtems_status_code rtems_timer_create( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - timer created successfully +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - invalid timer name +``RTEMS_TOO_MANY`` - too many timers created + +**DESCRIPTION:** + +This directive creates a timer. The assigned timer +id is returned in id. This id is used to access the timer with +other timer manager directives. For control and maintenance of +the timer, RTEMS allocates a TMCB from the local TMCB free pool +and initializes it. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +TIMER_IDENT - Get ID of a timer +------------------------------- +.. index:: obtain the ID of a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_ident + +.. code:: c + + rtems_status_code rtems_timer_ident( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - timer identified successfully +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - timer name not found + +**DESCRIPTION:** + +This directive obtains the timer id associated with +the timer name to be acquired. If the timer name is not unique, +then the timer id will match one of the timers with that name. +However, this timer id is not guaranteed to correspond to the +desired timer. The timer id is used to access this timer in +other timer related directives. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +TIMER_CANCEL - Cancel a timer +----------------------------- +.. index:: cancel a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_cancel + +.. code:: c + + rtems_status_code rtems_timer_cancel( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - timer canceled successfully +``RTEMS_INVALID_ID`` - invalid timer id + +**DESCRIPTION:** + +This directive cancels the timer id. This timer will +be reinitiated by the next invocation of ``rtems_timer_reset``,``rtems_timer_fire_after``, or``rtems_timer_fire_when`` with this id. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +TIMER_DELETE - Delete a timer +----------------------------- +.. index:: delete a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_delete + +.. code:: c + + rtems_status_code rtems_timer_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - timer deleted successfully +``RTEMS_INVALID_ID`` - invalid timer id + +**DESCRIPTION:** + +This directive deletes the timer specified by id. If +the timer is running, it is automatically canceled. The TMCB +for the deleted timer is reclaimed by RTEMS. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +A timer can be deleted by a task other than the task +which created the timer. + +TIMER_FIRE_AFTER - Fire timer after interval +-------------------------------------------- +.. index:: fire a timer after an interval + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_fire_after + +.. code:: c + + rtems_status_code rtems_timer_fire_after( + rtems_id id, + rtems_interval ticks, + rtems_timer_service_routine_entry routine, + void \*user_data + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - timer initiated successfully +``RTEMS_INVALID_ADDRESS`` - ``routine`` is NULL +``RTEMS_INVALID_ID`` - invalid timer id +``RTEMS_INVALID_NUMBER`` - invalid interval + +**DESCRIPTION:** + +This directive initiates the timer specified by id. +If the timer is running, it is automatically canceled before +being initiated. The timer is scheduled to fire after an +interval ticks clock ticks has passed. When the timer fires, +the timer service routine routine will be invoked with the +argument user_data. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +TIMER_FIRE_WHEN - Fire timer when specified +------------------------------------------- +.. index:: fire a timer at wall time + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_fire_when + +.. code:: c + + rtems_status_code rtems_timer_fire_when( + rtems_id id, + rtems_time_of_day \*wall_time, + rtems_timer_service_routine_entry routine, + void \*user_data + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - timer initiated successfully +``RTEMS_INVALID_ADDRESS`` - ``routine`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``wall_time`` is NULL +``RTEMS_INVALID_ID`` - invalid timer id +``RTEMS_NOT_DEFINED`` - system date and time is not set +``RTEMS_INVALID_CLOCK`` - invalid time of day + +**DESCRIPTION:** + +This directive initiates the timer specified by id. +If the timer is running, it is automatically canceled before +being initiated. The timer is scheduled to fire at the time of +day specified by wall_time. When the timer fires, the timer +service routine routine will be invoked with the argument +user_data. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +TIMER_INITIATE_SERVER - Initiate server for task-based timers +------------------------------------------------------------- +.. index:: initiate the Timer Server + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_initiate_server + +.. code:: c + + rtems_status_code rtems_timer_initiate_server( + uint32_t priority, + uint32_t stack_size, + rtems_attribute attribute_set + ) + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - Timer Server initiated successfully +``RTEMS_TOO_MANY`` - too many tasks created + +**DESCRIPTION:** + +This directive initiates the Timer Server task. This task +is responsible for executing all timers initiated via the``rtems_timer_server_fire_after`` or``rtems_timer_server_fire_when`` directives. + +**NOTES:** + +This directive could cause the calling task to be preempted. + +The Timer Server task is created using the``rtems_task_create`` service and must be accounted +for when configuring the system. + +Even through this directive invokes the ``rtems_task_create`` +and ``rtems_task_start`` directives, it should only fail +due to resource allocation problems. + +TIMER_SERVER_FIRE_AFTER - Fire task-based timer after interval +-------------------------------------------------------------- +.. index:: fire task-based a timer after an interval + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_server_fire_after + +.. code:: c + + rtems_status_code rtems_timer_server_fire_after( + rtems_id id, + rtems_interval ticks, + rtems_timer_service_routine_entry routine, + void \*user_data + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - timer initiated successfully +``RTEMS_INVALID_ADDRESS`` - ``routine`` is NULL +``RTEMS_INVALID_ID`` - invalid timer id +``RTEMS_INVALID_NUMBER`` - invalid interval +``RTEMS_INCORRECT_STATE`` - Timer Server not initiated + +**DESCRIPTION:** + +This directive initiates the timer specified by id and specifies +that when it fires it will be executed by the Timer Server. + +If the timer is running, it is automatically canceled before +being initiated. The timer is scheduled to fire after an +interval ticks clock ticks has passed. When the timer fires, +the timer service routine routine will be invoked with the +argument user_data. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +TIMER_SERVER_FIRE_WHEN - Fire task-based timer when specified +------------------------------------------------------------- +.. index:: fire a task-based timer at wall time + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_server_fire_when + +.. code:: c + + rtems_status_code rtems_timer_server_fire_when( + rtems_id id, + rtems_time_of_day \*wall_time, + rtems_timer_service_routine_entry routine, + void \*user_data + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - timer initiated successfully +``RTEMS_INVALID_ADDRESS`` - ``routine`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``wall_time`` is NULL +``RTEMS_INVALID_ID`` - invalid timer id +``RTEMS_NOT_DEFINED`` - system date and time is not set +``RTEMS_INVALID_CLOCK`` - invalid time of day +``RTEMS_INCORRECT_STATE`` - Timer Server not initiated + +**DESCRIPTION:** + +This directive initiates the timer specified by id and specifies +that when it fires it will be executed by the Timer Server. + +If the timer is running, it is automatically canceled before +being initiated. The timer is scheduled to fire at the time of +day specified by wall_time. When the timer fires, the timer +service routine routine will be invoked with the argument +user_data. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +TIMER_RESET - Reset an interval timer +------------------------------------- +.. index:: reset a timer + +**CALLING SEQUENCE:** + +.. index:: rtems_timer_reset + +.. code:: c + + rtems_status_code rtems_timer_reset( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - timer reset successfully +``RTEMS_INVALID_ID`` - invalid timer id +``RTEMS_NOT_DEFINED`` - attempted to reset a when or newly created timer + +**DESCRIPTION:** + +This directive resets the timer associated with id. +This timer must have been previously initiated with either the``rtems_timer_fire_after`` or``rtems_timer_server_fire_after`` +directive. If active the timer is canceled, +after which the timer is reinitiated using the same interval and +timer service routine which the original``rtems_timer_fire_after````rtems_timer_server_fire_after`` +directive used. + +**NOTES:** + +If the timer has not been used or the last usage of this timer +was by a ``rtems_timer_fire_when`` or``rtems_timer_server_fire_when`` +directive, then the ``RTEMS_NOT_DEFINED`` error is +returned. + +Restarting a cancelled after timer results in the timer being +reinitiated with its previous timer service routine and interval. + +This directive will not cause the running task to be preempted. + +.. COMMENT: COPYRIGHT (c) 1988-2013. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +.. COMMENT: Open Issues + +.. COMMENT: - nicen up the tables + +.. COMMENT: - use math mode to print formulas + +Rate Monotonic Manager +###################### + +.. index:: rate mononitonic tasks +.. index:: periodic tasks + +Introduction +============ + +The rate monotonic manager provides facilities to implement tasks which execute +in a periodic fashion. Critically, it also gathers information about the +execution of those periods and can provide important statistics to the +user which can be used to analyze and tune the application. The directives +provided by the rate monotonic manager are: + +- ``rtems_rate_monotonic_create`` - Create a rate monotonic period + +- ``rtems_rate_monotonic_ident`` - Get ID of a period + +- ``rtems_rate_monotonic_cancel`` - Cancel a period + +- ``rtems_rate_monotonic_delete`` - Delete a rate monotonic period + +- ``rtems_rate_monotonic_period`` - Conclude current/Start next period + +- ``rtems_rate_monotonic_get_status`` - Obtain status from a period + +- ``rtems_rate_monotonic_get_statistics`` - Obtain statistics from a period + +- ``rtems_rate_monotonic_reset_statistics`` - Reset statistics for a period + +- ``rtems_rate_monotonic_reset_all_statistics`` - Reset statistics for all periods + +- ``rtems_rate_monotonic_report_statistics`` - Print period statistics report + +Background +========== + +The rate monotonic manager provides facilities to +manage the execution of periodic tasks. This manager was +designed to support application designers who utilize the Rate +Monotonic Scheduling Algorithm (RMS) to ensure that their +periodic tasks will meet their deadlines, even under transient +overload conditions. Although designed for hard real-time +systems, the services provided by the rate monotonic manager may +be used by any application which requires periodic tasks. + +Rate Monotonic Manager Required Support +--------------------------------------- + +A clock tick is required to support the functionality provided by this manager. + +Period Statistics +----------------- + +This manager maintains a set of statistics on each period object. These +statistics are reset implictly at period creation time and may be reset or +obtained at any time by the application. The following is a list of the +information kept: + +- ``owner`` + is the id of the thread that owns this period. + +- ``count`` + is the total number of periods executed. + +- ``missed_count`` + is the number of periods that were missed. + +- ``min_cpu_time`` + is the minimum amount of CPU execution time consumed + on any execution of the periodic loop. + +- ``max_cpu_time`` + is the maximum amount of CPU execution time consumed + on any execution of the periodic loop. + +- ``total_cpu_time`` + is the total amount of CPU execution time consumed + by executions of the periodic loop. + +- ``min_wall_time`` + is the minimum amount of wall time that passed + on any execution of the periodic loop. + +- ``max_wall_time`` + is the maximum amount of wall time that passed + on any execution of the periodic loop. + +- ``total_wall_time`` + is the total amount of wall time that passed + during executions of the periodic loop. + +Each period is divided into two consecutive phases. The period starts with the +active phase of the task and is followed by the inactive phase of the task. In +the inactive phase the task is blocked and waits for the start of the next +period. The inactive phase is skipped in case of a period miss. The wall time +includes the time during the active phase of the task on which the task is not +executing on a processor. The task is either blocked (for example it waits for +a resource) or a higher priority tasks executes, thus preventing it from +executing. In case the wall time exceeds the period time, then this is a +period miss. The gap between the wall time and the period time is the margin +between a period miss or success. + +The period statistics information is inexpensive to maintain +and can provide very useful insights into the execution +characteristics of a periodic task loop. But it is just information. +The period statistics reported must be analyzed by the user in terms +of what the applications is. For example, in an application where +priorities are assigned by the Rate Monotonic Algorithm, it would +be very undesirable for high priority (i.e. frequency) tasks to +miss their period. Similarly, in nearly any application, if a +task were supposed to execute its periodic loop every 10 milliseconds +and it averaged 11 milliseconds, then application requirements +are not being met. + +The information reported can be used to determine the "hot spots" +in the application. Given a period’s id, the user can determine +the length of that period. From that information and the CPU usage, +the user can calculate the percentage of CPU time consumed by that +periodic task. For example, a task executing for 20 milliseconds +every 200 milliseconds is consuming 10 percent of the processor’s +execution time. This is usually enough to make it a good candidate +for optimization. + +However, execution time alone is not enough to gauge the value of +optimizing a particular task. It is more important to optimize +a task executing 2 millisecond every 10 milliseconds (20 percent +of the CPU) than one executing 10 milliseconds every 100 (10 percent +of the CPU). As a general rule of thumb, the higher frequency at +which a task executes, the more important it is to optimize that +task. + +Rate Monotonic Manager Definitions +---------------------------------- +.. index:: periodic task, definition + +A periodic task is one which must be executed at a +regular interval. The interval between successive iterations of +the task is referred to as its period. Periodic tasks can be +characterized by the length of their period and execution time. +The period and execution time of a task can be used to determine +the processor utilization for that task. Processor utilization +is the percentage of processor time used and can be calculated +on a per-task or system-wide basis. Typically, the task’s +worst-case execution time will be less than its period. For +example, a periodic task’s requirements may state that it should +execute for 10 milliseconds every 100 milliseconds. Although +the execution time may be the average, worst, or best case, the +worst-case execution time is more appropriate for use when +analyzing system behavior under transient overload conditions... index:: aperiodic task, definition + +In contrast, an aperiodic task executes at irregular +intervals and has only a soft deadline. In other words, the +deadlines for aperiodic tasks are not rigid, but adequate +response times are desirable. For example, an aperiodic task +may process user input from a terminal... index:: sporadic task, definition + +Finally, a sporadic task is an aperiodic task with a +hard deadline and minimum interarrival time. The minimum +interarrival time is the minimum period of time which exists +between successive iterations of the task. For example, a +sporadic task could be used to process the pressing of a fire +button on a joystick. The mechanical action of the fire button +ensures a minimum time period between successive activations, +but the missile must be launched by a hard deadline. + +Rate Monotonic Scheduling Algorithm +----------------------------------- +.. index:: Rate Monotonic Scheduling Algorithm, definition +.. index:: RMS Algorithm, definition + +The Rate Monotonic Scheduling Algorithm (RMS) is +important to real-time systems designers because it allows one +to guarantee that a set of tasks is schedulable. A set of tasks +is said to be schedulable if all of the tasks can meet their +deadlines. RMS provides a set of rules which can be used to +perform a guaranteed schedulability analysis for a task set. +This analysis determines whether a task set is schedulable under +worst-case conditions and emphasizes the predictability of the +system’s behavior. It has been proven that: + +- *RMS is an optimal static priority algorithm for + scheduling independent, preemptible, periodic tasks + on a single processor.* + +RMS is optimal in the sense that if a set of tasks +can be scheduled by any static priority algorithm, then RMS will +be able to schedule that task set. RMS bases it schedulability +analysis on the processor utilization level below which all +deadlines can be met. + +RMS calls for the static assignment of task +priorities based upon their period. The shorter a task’s +period, the higher its priority. For example, a task with a 1 +millisecond period has higher priority than a task with a 100 +millisecond period. If two tasks have the same period, then RMS +does not distinguish between the tasks. However, RTEMS +specifies that when given tasks of equal priority, the task +which has been ready longest will execute first. RMS’s priority +assignment scheme does not provide one with exact numeric values +for task priorities. For example, consider the following task +set and priority assignments: + ++--------------------+---------------------+---------------------+ +| Task | Period | Priority | +| | (in milliseconds) | | ++====================+=====================+=====================+ +| 1 | 100 | Low | ++--------------------+---------------------+---------------------+ +| 2 | 50 | Medium | ++--------------------+---------------------+---------------------+ +| 3 | 50 | Medium | ++--------------------+---------------------+---------------------+ +| 4 | 25 | High | ++--------------------+---------------------+---------------------+ + +RMS only calls for task 1 to have the lowest +priority, task 4 to have the highest priority, and tasks 2 and 3 +to have an equal priority between that of tasks 1 and 4. The +actual RTEMS priorities assigned to the tasks must only adhere +to those guidelines. + +Many applications have tasks with both hard and soft +deadlines. The tasks with hard deadlines are typically referred +to as the critical task set, with the soft deadline tasks being +the non-critical task set. The critical task set can be +scheduled using RMS, with the non-critical tasks not executing +under transient overload, by simply assigning priorities such +that the lowest priority critical task (i.e. longest period) has +a higher priority than the highest priority non-critical task. +Although RMS may be used to assign priorities to the +non-critical tasks, it is not necessary. In this instance, +schedulability is only guaranteed for the critical task set. + +Schedulability Analysis +----------------------- + +.. index:: RMS schedulability analysis + +RMS allows application designers to ensure that tasks +can meet all deadlines, even under transient overload, without +knowing exactly when any given task will execute by applying +proven schedulability analysis rules. + +Assumptions +~~~~~~~~~~~ + +The schedulability analysis rules for RMS were +developed based on the following assumptions: + +- The requests for all tasks for which hard deadlines + exist are periodic, with a constant interval between requests. + +- Each task must complete before the next request for it + occurs. + +- The tasks are independent in that a task does not depend + on the initiation or completion of requests for other tasks. + +- The execution time for each task without preemption or + interruption is constant and does not vary. + +- Any non-periodic tasks in the system are special. These + tasks displace periodic tasks while executing and do not have + hard, critical deadlines. + +Once the basic schedulability analysis is understood, +some of the above assumptions can be relaxed and the +side-effects accounted for. + +Processor Utilization Rule +~~~~~~~~~~~~~~~~~~~~~~~~~~ +.. index:: RMS Processor Utilization Rule + +The Processor Utilization Rule requires that +processor utilization be calculated based upon the period and +execution time of each task. The fraction of processor time +spent executing task index is Time(index) / Period(index). The +processor utilization can be calculated as follows: +.. code:: c + + Utilization = 0 + for index = 1 to maximum_tasks + Utilization = Utilization + (Time(index)/Period(index)) + +To ensure schedulability even under transient +overload, the processor utilization must adhere to the following +rule: +.. code:: c + + Utilization = maximum_tasks * (2**(1/maximum_tasks) - 1) + +As the number of tasks increases, the above formula +approaches ln(2) for a worst-case utilization factor of +approximately 0.693. Many tasks sets can be scheduled with a +greater utilization factor. In fact, the average processor +utilization threshold for a randomly generated task set is +approximately 0.88. + +Processor Utilization Rule Example +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +This example illustrates the application of the +Processor Utilization Rule to an application with three critical +periodic tasks. The following table details the RMS priority, +period, execution time, and processor utilization for each task: + + ++------------+----------+--------+-----------+-------------+ +| Tas k | RMS | Period | Execution | Processor | +| | Priority | | Time | Utilization | ++============+==========+========+===========+=============+ +| 1 | High | 100 | 15 | 0.15 | ++------------+----------+--------+-----------+-------------+ +| 2 | Medium | 200 | 50 | 0.25 | ++------------+----------+--------+-----------+-------------+ +| 3 | Low | 300 | 100 | 0.33 | ++------------+----------+--------+-----------+-------------+ + +The total processor utilization for this task set is +0.73 which is below the upper bound of 3 * (2**(1/3) - 1), or +0.779, imposed by the Processor Utilization Rule. Therefore, +this task set is guaranteed to be schedulable using RMS. + +First Deadline Rule +~~~~~~~~~~~~~~~~~~~ +.. index:: RMS First Deadline Rule + +If a given set of tasks do exceed the processor +utilization upper limit imposed by the Processor Utilization +Rule, they can still be guaranteed to meet all their deadlines +by application of the First Deadline Rule. This rule can be +stated as follows: + +For a given set of independent periodic tasks, if +each task meets its first deadline when all tasks are started at +the same time, then the deadlines will always be met for any +combination of start times. + +A key point with this rule is that ALL periodic tasks +are assumed to start at the exact same instant in time. +Although this assumption may seem to be invalid, RTEMS makes it +quite easy to ensure. By having a non-preemptible user +initialization task, all application tasks, regardless of +priority, can be created and started before the initialization +deletes itself. This technique ensures that all tasks begin to +compete for execution time at the same instant – when the user +initialization task deletes itself. + +First Deadline Rule Example +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The First Deadline Rule can ensure schedulability +even when the Processor Utilization Rule fails. The example +below is a modification of the Processor Utilization Rule +example where task execution time has been increased from 15 to +25 units. The following table details the RMS priority, period, +execution time, and processor utilization for each task: +.. code:: c + ++------------+----------+--------+-----------+-------------+ +| Task | RMS | Period | Execution | Processor | +| | Priority | | Time | Utilization | ++============+==========+========+===========+=============+ +| 1 | High | 100 | 25 | 0.25 | ++------------+----------+--------+-----------+-------------+ +| 2 | Medium | 200 | 50 | 0.25 | ++------------+----------+--------+-----------+-------------+ +| 3 | Low | 300 | 100 | 0.33 | ++------------+----------+--------+-----------+-------------+ + +The total processor utilization for the modified task +set is 0.83 which is above the upper bound of 3 * (2**(1/3) - 1), +or 0.779, imposed by the Processor Utilization Rule. Therefore, +this task set is not guaranteed to be schedulable using RMS. +However, the First Deadline Rule can guarantee the +schedulability of this task set. This rule calls for one to +examine each occurrence of deadline until either all tasks have +met their deadline or one task failed to meet its first +deadline. The following table details the time of each deadline +occurrence, the maximum number of times each task may have run, +the total execution time, and whether all the deadlines have +been met. +.. code:: c + ++----------+------+------+------+----------------------+---------------+ +| Deadline | Task | Task | Task | Total | All Deadlines | +| Time | 1 | 2 | 3 | Execution Time | Met? | ++==========+======+======+======+======================+===============+ +| 100 | 1 | 1 | 1 | 25 + 50 + 100 = 175 | NO | ++----------+------+------+------+----------------------+---------------+ +| 200 | 2 | 1 | 1 | 50 + 50 + 100 = 200 | YES | ++----------+------+------+------+----------------------+---------------+ + +The key to this analysis is to recognize when each +task will execute. For example at time 100, task 1 must have +met its first deadline, but tasks 2 and 3 may also have begun +execution. In this example, at time 100 tasks 1 and 2 have +completed execution and thus have met their first deadline. +Tasks 1 and 2 have used (25 + 50) = 75 time units, leaving (100 +- 75) = 25 time units for task 3 to begin. Because task 3 takes +100 ticks to execute, it will not have completed execution at +time 100. Thus at time 100, all of the tasks except task 3 have +met their first deadline. + +At time 200, task 1 must have met its second deadline +and task 2 its first deadline. As a result, of the first 200 +time units, task 1 uses (2 * 25) = 50 and task 2 uses 50, +leaving (200 - 100) time units for task 3. Task 3 requires 100 +time units to execute, thus it will have completed execution at +time 200. Thus, all of the tasks have met their first deadlines +at time 200, and the task set is schedulable using the First +Deadline Rule. + +Relaxation of Assumptions +~~~~~~~~~~~~~~~~~~~~~~~~~ + +The assumptions used to develop the RMS +schedulability rules are uncommon in most real-time systems. +For example, it was assumed that tasks have constant unvarying +execution time. It is possible to relax this assumption, simply +by using the worst-case execution time of each task. + +Another assumption is that the tasks are independent. +This means that the tasks do not wait for one another or +contend for resources. This assumption can be relaxed by +accounting for the amount of time a task spends waiting to +acquire resources. Similarly, each task’s execution time must +account for any I/O performed and any RTEMS directive calls. + +In addition, the assumptions did not account for the +time spent executing interrupt service routines. This can be +accounted for by including all the processor utilization by +interrupt service routines in the utilization calculation. +Similarly, one should also account for the impact of delays in +accessing local memory caused by direct memory access and other +processors accessing local dual-ported memory. + +The assumption that nonperiodic tasks are used only +for initialization or failure-recovery can be relaxed by placing +all periodic tasks in the critical task set. This task set can +be scheduled and analyzed using RMS. All nonperiodic tasks are +placed in the non-critical task set. Although the critical task +set can be guaranteed to execute even under transient overload, +the non-critical task set is not guaranteed to execute. + +In conclusion, the application designer must be fully +cognizant of the system and its run-time behavior when +performing schedulability analysis for a system using RMS. +Every hardware and software factor which impacts the execution +time of each task must be accounted for in the schedulability +analysis. + +Further Reading +~~~~~~~~~~~~~~~ + +For more information on Rate Monotonic Scheduling and +its schedulability analysis, the reader is referred to the +following: + +- *C. L. Liu and J. W. Layland. "Scheduling Algorithms for + Multiprogramming in a Hard Real Time Environment." *Journal of + the Association of Computing Machinery*. January 1973. pp. 46-61.* + +- *John Lehoczky, Lui Sha, and Ye Ding. "The Rate Monotonic + Scheduling Algorithm: Exact Characterization and Average Case + Behavior." *IEEE Real-Time Systems Symposium*. 1989. pp. 166-171.* + +- *Lui Sha and John Goodenough. "Real-Time Scheduling + theory and Ada." *IEEE Computer*. April 1990. pp. 53-62.* + +- *Alan Burns. "Scheduling hard real-time systems: a + review." *Software Engineering Journal*. May 1991. pp. 116-128.* + +Operations +========== + +Creating a Rate Monotonic Period +-------------------------------- + +The ``rtems_rate_monotonic_create`` directive creates a rate +monotonic period which is to be used by the calling task to +delineate a period. RTEMS allocates a Period Control Block +(PCB) from the PCB free list. This data structure is used by +RTEMS to manage the newly created rate monotonic period. RTEMS +returns a unique period ID to the application which is used by +other rate monotonic manager directives to access this rate +monotonic period. + +Manipulating a Period +--------------------- + +The ``rtems_rate_monotonic_period`` directive is used to +establish and maintain periodic execution utilizing a previously +created rate monotonic period. Once initiated by the``rtems_rate_monotonic_period`` directive, the period is +said to run until it either expires or is reinitiated. The state of the rate +monotonic period results in one of the following scenarios: + +- If the rate monotonic period is running, the calling + task will be blocked for the remainder of the outstanding period + and, upon completion of that period, the period will be + reinitiated with the specified period. + +- If the rate monotonic period is not currently running + and has not expired, it is initiated with a length of period + ticks and the calling task returns immediately. + +- If the rate monotonic period has expired before the task + invokes the ``rtems_rate_monotonic_period`` directive, + the period will be initiated with a length of period ticks and the calling task + returns immediately with a timeout error status. + +Obtaining the Status of a Period +-------------------------------- + +If the ``rtems_rate_monotonic_period`` directive is invoked +with a period of ``RTEMS_PERIOD_STATUS`` ticks, the current +state of the specified rate monotonic period will be returned. The following +table details the relationship between the period’s status and +the directive status code returned by the``rtems_rate_monotonic_period`` +directive: + +- ``RTEMS_SUCCESSFUL`` - period is running + +- ``RTEMS_TIMEOUT`` - period has expired + +- ``RTEMS_NOT_DEFINED`` - period has never been initiated + +Obtaining the status of a rate monotonic period does +not alter the state or length of that period. + +Canceling a Period +------------------ + +The ``rtems_rate_monotonic_cancel`` directive is used to stop +the period maintained by the specified rate monotonic period. +The period is stopped and the rate monotonic period can be +reinitiated using the ``rtems_rate_monotonic_period`` directive. + +Deleting a Rate Monotonic Period +-------------------------------- + +The ``rtems_rate_monotonic_delete`` directive is used to delete +a rate monotonic period. If the period is running and has not +expired, the period is automatically canceled. The rate +monotonic period’s control block is returned to the PCB free +list when it is deleted. A rate monotonic period can be deleted +by a task other than the task which created the period. + +Examples +-------- + +The following sections illustrate common uses of rate +monotonic periods to construct periodic tasks. + +Simple Periodic Task +-------------------- + +This example consists of a single periodic task +which, after initialization, executes every 100 clock ticks. +.. code:: c + + rtems_task Periodic_task(rtems_task_argument arg) + { + rtems_name name; + rtems_id period; + rtems_status_code status; + name = rtems_build_name( 'P', 'E', 'R', 'D' ); + status = rtems_rate_monotonic_create( name, &period ); + if ( status != RTEMS_STATUS_SUCCESSFUL ) { + printf( "rtems_monotonic_create failed with status of %d.\\n", rc ); + exit( 1 ); + } + while ( 1 ) { + if ( rtems_rate_monotonic_period( period, 100 ) == RTEMS_TIMEOUT ) + break; + /* Perform some periodic actions \*/ + } + /* missed period so delete period and SELF \*/ + status = rtems_rate_monotonic_delete( period ); + if ( status != RTEMS_STATUS_SUCCESSFUL ) { + printf( "rtems_rate_monotonic_delete failed with status of %d.\\n", status ); + exit( 1 ); + } + status = rtems_task_delete( SELF ); /* should not return \*/ + printf( "rtems_task_delete returned with status of %d.\\n", status ); + exit( 1 ); + } + +The above task creates a rate monotonic period as +part of its initialization. The first time the loop is +executed, the ``rtems_rate_monotonic_period`` +directive will initiate the period for 100 ticks and return +immediately. Subsequent invocations of the``rtems_rate_monotonic_period`` directive will result +in the task blocking for the remainder of the 100 tick period. +If, for any reason, the body of the loop takes more than 100 +ticks to execute, the ``rtems_rate_monotonic_period`` +directive will return the ``RTEMS_TIMEOUT`` status. +If the above task misses its deadline, it will delete the rate +monotonic period and itself. + +Task with Multiple Periods +-------------------------- + +This example consists of a single periodic task +which, after initialization, performs two sets of actions every +100 clock ticks. The first set of actions is performed in the +first forty clock ticks of every 100 clock ticks, while the +second set of actions is performed between the fortieth and +seventieth clock ticks. The last thirty clock ticks are not +used by this task. +.. code:: c + + rtems_task Periodic_task(rtems_task_argument arg) + { + rtems_name name_1, name_2; + rtems_id period_1, period_2; + rtems_status_code status; + name_1 = rtems_build_name( 'P', 'E', 'R', '1' ); + name_2 = rtems_build_name( 'P', 'E', 'R', '2' ); + (void ) rtems_rate_monotonic_create( name_1, &period_1 ); + (void ) rtems_rate_monotonic_create( name_2, &period_2 ); + while ( 1 ) { + if ( rtems_rate_monotonic_period( period_1, 100 ) == TIMEOUT ) + break; + if ( rtems_rate_monotonic_period( period_2, 40 ) == TIMEOUT ) + break; + /* + * Perform first set of actions between clock + * ticks 0 and 39 of every 100 ticks. + \*/ + if ( rtems_rate_monotonic_period( period_2, 30 ) == TIMEOUT ) + break; + /* + * Perform second set of actions between clock 40 and 69 + * of every 100 ticks. THEN ... + * + * Check to make sure we didn't miss the period_2 period. + \*/ + if ( rtems_rate_monotonic_period( period_2, STATUS ) == TIMEOUT ) + break; + (void) rtems_rate_monotonic_cancel( period_2 ); + } + /* missed period so delete period and SELF \*/ + (void ) rtems_rate_monotonic_delete( period_1 ); + (void ) rtems_rate_monotonic_delete( period_2 ); + (void ) task_delete( SELF ); + } + +The above task creates two rate monotonic periods as +part of its initialization. The first time the loop is +executed, the ``rtems_rate_monotonic_period`` +directive will initiate the period_1 period for 100 ticks +and return immediately. Subsequent invocations of the``rtems_rate_monotonic_period`` directive +for period_1 will result in the task blocking for the remainder +of the 100 tick period. The period_2 period is used to control +the execution time of the two sets of actions within each 100 +tick period established by period_1. The``rtems_rate_monotonic_cancel( period_2 )`` +call is performed to ensure that the period_2 period +does not expire while the task is blocked on the period_1 +period. If this cancel operation were not performed, every time +the ``rtems_rate_monotonic_period( period_2, 40 )`` +call is executed, except for the initial one, a directive status +of ``RTEMS_TIMEOUT`` is returned. It is important to +note that every time this call is made, the period_2 period will be +initiated immediately and the task will not block. + +If, for any reason, the task misses any deadline, the``rtems_rate_monotonic_period`` directive will +return the ``RTEMS_TIMEOUT`` +directive status. If the above task misses its deadline, it +will delete the rate monotonic periods and itself. + +Directives +========== + +This section details the rate monotonic manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +RATE_MONOTONIC_CREATE - Create a rate monotonic period +------------------------------------------------------ +.. index:: create a period + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_create + +.. code:: c + + rtems_status_code rtems_rate_monotonic_create( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - rate monotonic period created successfully +``RTEMS_INVALID_NAME`` - invalid period name +``RTEMS_TOO_MANY`` - too many periods created + +**DESCRIPTION:** + +This directive creates a rate monotonic period. The +assigned rate monotonic id is returned in id. This id is used +to access the period with other rate monotonic manager +directives. For control and maintenance of the rate monotonic +period, RTEMS allocates a PCB from the local PCB free pool and +initializes it. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +RATE_MONOTONIC_IDENT - Get ID of a period +----------------------------------------- +.. index:: get ID of a period +.. index:: obtain ID of a period + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_ident + +.. code:: c + + rtems_status_code rtems_rate_monotonic_ident( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - period identified successfully +``RTEMS_INVALID_NAME`` - period name not found + +**DESCRIPTION:** + +This directive obtains the period id associated with +the period name to be acquired. If the period name is not +unique, then the period id will match one of the periods with +that name. However, this period id is not guaranteed to +correspond to the desired period. The period id is used to +access this period in other rate monotonic manager directives. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +RATE_MONOTONIC_CANCEL - Cancel a period +--------------------------------------- +.. index:: cancel a period + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_cancel + +.. code:: c + + rtems_status_code rtems_rate_monotonic_cancel( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - period canceled successfully +``RTEMS_INVALID_ID`` - invalid rate monotonic period id +``RTEMS_NOT_OWNER_OF_RESOURCE`` - rate monotonic period not created by calling task + +**DESCRIPTION:** + +This directive cancels the rate monotonic period id. +This period will be reinitiated by the next invocation of``rtems_rate_monotonic_period`` with id. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +The rate monotonic period specified by id must have +been created by the calling task. + +RATE_MONOTONIC_DELETE - Delete a rate monotonic period +------------------------------------------------------ +.. index:: delete a period + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_delete + +.. code:: c + + rtems_status_code rtems_rate_monotonic_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - period deleted successfully +``RTEMS_INVALID_ID`` - invalid rate monotonic period id + +**DESCRIPTION:** + +This directive deletes the rate monotonic period +specified by id. If the period is running, it is automatically +canceled. The PCB for the deleted period is reclaimed by RTEMS. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +A rate monotonic period can be deleted by a task +other than the task which created the period. + +RATE_MONOTONIC_PERIOD - Conclude current/Start next period +---------------------------------------------------------- +.. index:: conclude current period +.. index:: start current period +.. index:: period initiation + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_period + +.. code:: c + + rtems_status_code rtems_rate_monotonic_period( + rtems_id id, + rtems_interval length + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - period initiated successfully +``RTEMS_INVALID_ID`` - invalid rate monotonic period id +``RTEMS_NOT_OWNER_OF_RESOURCE`` - period not created by calling task +``RTEMS_NOT_DEFINED`` - period has never been initiated (only +possible when period is set to PERIOD_STATUS) +``RTEMS_TIMEOUT`` - period has expired + +**DESCRIPTION:** + +This directive initiates the rate monotonic period id +with a length of period ticks. If id is running, then the +calling task will block for the remainder of the period before +reinitiating the period with the specified period. If id was +not running (either expired or never initiated), the period is +immediately initiated and the directive returns immediately. + +If invoked with a period of ``RTEMS_PERIOD_STATUS`` ticks, the +current state of id will be returned. The directive status +indicates the current state of the period. This does not alter +the state or period of the period. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +RATE_MONOTONIC_GET_STATUS - Obtain status from a period +------------------------------------------------------- +.. index:: get status of period +.. index:: obtain status of period + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_get_status + +.. code:: c + + rtems_status_code rtems_rate_monotonic_get_status( + rtems_id id, + rtems_rate_monotonic_period_status \*status + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - period initiated successfully +``RTEMS_INVALID_ID`` - invalid rate monotonic period id +``RTEMS_INVALID_ADDRESS`` - invalid address of status + +**DESCRIPTION:** + +This directive returns status information associated with +the rate monotonic period id in the following data structure:.. index:: rtems_rate_monotonic_period_status + +.. code:: c + + typedef struct { + rtems_id owner; + rtems_rate_monotonic_period_states state; + rtems_rate_monotonic_period_time_t since_last_period; + rtems_thread_cpu_usage_t executed_since_last_period; + } rtems_rate_monotonic_period_status; + +.. COMMENT: RATE_MONOTONIC_INACTIVE does not have RTEMS_ in front of it. + +A configure time option can be used to select whether the time information is +given in ticks or seconds and nanoseconds. The default is seconds and +nanoseconds. If the period’s state is ``RATE_MONOTONIC_INACTIVE``, both +time values will be set to 0. Otherwise, both time values will contain +time information since the last invocation of the``rtems_rate_monotonic_period`` directive. More +specifically, the ticks_since_last_period value contains the elapsed time +which has occurred since the last invocation of the``rtems_rate_monotonic_period`` directive and the +ticks_executed_since_last_period contains how much processor time the +owning task has consumed since the invocation of the``rtems_rate_monotonic_period`` directive. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +RATE_MONOTONIC_GET_STATISTICS - Obtain statistics from a period +--------------------------------------------------------------- +.. index:: get statistics of period +.. index:: obtain statistics of period + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_get_statistics + +.. code:: c + + rtems_status_code rtems_rate_monotonic_get_statistics( + rtems_id id, + rtems_rate_monotonic_period_statistics \*statistics + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - period initiated successfully +``RTEMS_INVALID_ID`` - invalid rate monotonic period id +``RTEMS_INVALID_ADDRESS`` - invalid address of statistics + +**DESCRIPTION:** + +This directive returns statistics information associated with +the rate monotonic period id in the following data structure:.. index:: rtems_rate_monotonic_period_statistics + +.. code:: c + + typedef struct { + uint32_t count; + uint32_t missed_count; + #ifdef RTEMS_ENABLE_NANOSECOND_CPU_USAGE_STATISTICS + struct timespec min_cpu_time; + struct timespec max_cpu_time; + struct timespec total_cpu_time; + #else + uint32_t min_cpu_time; + uint32_t max_cpu_time; + uint32_t total_cpu_time; + #endif + #ifdef RTEMS_ENABLE_NANOSECOND_RATE_MONOTONIC_STATISTICS + struct timespec min_wall_time; + struct timespec max_wall_time; + struct timespec total_wall_time; + #else + uint32_t min_wall_time; + uint32_t max_wall_time; + uint32_t total_wall_time; + #endif + } rtems_rate_monotonic_period_statistics; + +This directive returns the current statistics information for +the period instance assocaited with ``id``. The information +returned is indicated by the structure above. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +RATE_MONOTONIC_RESET_STATISTICS - Reset statistics for a period +--------------------------------------------------------------- +.. index:: reset statistics of period + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_reset_statistics + +.. code:: c + + rtems_status_code rtems_rate_monotonic_reset_statistics( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - period initiated successfully +``RTEMS_INVALID_ID`` - invalid rate monotonic period id + +**DESCRIPTION:** + +This directive resets the statistics information associated with +this rate monotonic period instance. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +RATE_MONOTONIC_RESET_ALL_STATISTICS - Reset statistics for all periods +---------------------------------------------------------------------- +.. index:: reset statistics of all periods + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_reset_all_statistics + +.. code:: c + + void rtems_rate_monotonic_reset_all_statistics(void); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive resets the statistics information associated with +all rate monotonic period instances. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +RATE_MONOTONIC_REPORT_STATISTICS - Print period statistics report +----------------------------------------------------------------- +.. index:: print period statistics report +.. index:: period statistics report + +**CALLING SEQUENCE:** + +.. index:: rtems_rate_monotonic_report_statistics + +.. code:: c + + void rtems_rate_monotonic_report_statistics(void); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive prints a report on all active periods which have +executed at least one period. The following is an example of the +output generated by this directive... index:: rtems_rate_monotonic_period_statistics + +.. code:: c + + ID OWNER PERIODS MISSED CPU TIME WALL TIME + MIN/MAX/AVG MIN/MAX/AVG + 0x42010001 TA1 502 0 0/1/0.99 0/0/0.00 + 0x42010002 TA2 502 0 0/1/0.99 0/0/0.00 + 0x42010003 TA3 501 0 0/1/0.99 0/0/0.00 + 0x42010004 TA4 501 0 0/1/0.99 0/0/0.00 + 0x42010005 TA5 10 0 0/1/0.90 0/0/0.00 + +**NOTES:** + +This directive will not cause the running task to be preempted. + +.. COMMENT: COPYRIGHT (c) 1988-2007. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Semaphore Manager +################# + +.. index:: semaphores +.. index:: binary semaphores +.. index:: counting semaphores +.. index:: mutual exclusion + +Introduction +============ + +The semaphore manager utilizes standard Dijkstra +counting semaphores to provide synchronization and mutual +exclusion capabilities. The directives provided by the +semaphore manager are: + +- ``rtems_semaphore_create`` - Create a semaphore + +- ``rtems_semaphore_ident`` - Get ID of a semaphore + +- ``rtems_semaphore_delete`` - Delete a semaphore + +- ``rtems_semaphore_obtain`` - Acquire a semaphore + +- ``rtems_semaphore_release`` - Release a semaphore + +- ``rtems_semaphore_flush`` - Unblock all tasks waiting on a semaphore + +- ``rtems_semaphore_set_priority`` - Set priority by + scheduler for a semaphore + +Background +========== + +A semaphore can be viewed as a protected variable +whose value can be modified only with the``rtems_semaphore_create``,``rtems_semaphore_obtain``, and``rtems_semaphore_release`` directives. RTEMS +supports both binary and counting semaphores. A binary semaphore +is restricted to values of zero or one, while a counting +semaphore can assume any non-negative integer value. + +A binary semaphore can be used to control access to a +single resource. In particular, it can be used to enforce +mutual exclusion for a critical section in user code. In this +instance, the semaphore would be created with an initial count +of one to indicate that no task is executing the critical +section of code. Upon entry to the critical section, a task +must issue the ``rtems_semaphore_obtain`` +directive to prevent other tasks from entering the critical section. +Upon exit from the critical section, the task must issue the``rtems_semaphore_release`` directive to +allow another task to execute the critical section. + +A counting semaphore can be used to control access to +a pool of two or more resources. For example, access to three +printers could be administered by a semaphore created with an +initial count of three. When a task requires access to one of +the printers, it issues the ``rtems_semaphore_obtain`` +directive to obtain access to a printer. If a printer is not currently +available, the task can wait for a printer to become available or return +immediately. When the task has completed printing, it should +issue the ``rtems_semaphore_release`` +directive to allow other tasks access to the printer. + +Task synchronization may be achieved by creating a +semaphore with an initial count of zero. One task waits for the +arrival of another task by issuing a ``rtems_semaphore_obtain`` +directive when it reaches a synchronization point. The other task +performs a corresponding ``rtems_semaphore_release`` +operation when it reaches its synchronization point, thus unblocking +the pending task. + +Nested Resource Access +---------------------- + +Deadlock occurs when a task owning a binary semaphore +attempts to acquire that same semaphore and blocks as result. +Since the semaphore is allocated to a task, it cannot be +deleted. Therefore, the task that currently holds the semaphore +and is also blocked waiting for that semaphore will never +execute again. + +RTEMS addresses this problem by allowing the task +holding the binary semaphore to obtain the same binary semaphore +multiple times in a nested manner. Each``rtems_semaphore_obtain`` must be accompanied with a``rtems_semaphore_release``. The semaphore will +only be made available for acquisition by other tasks when the +outermost ``rtems_semaphore_obtain`` is matched with +a ``rtems_semaphore_release``. + +Simple binary semaphores do not allow nested access and so can be used for task synchronization. + +Priority Inversion +------------------ + +Priority inversion is a form of indefinite +postponement which is common in multitasking, preemptive +executives with shared resources. Priority inversion occurs +when a high priority tasks requests access to shared resource +which is currently allocated to low priority task. The high +priority task must block until the low priority task releases +the resource. This problem is exacerbated when the low priority +task is prevented from executing by one or more medium priority +tasks. Because the low priority task is not executing, it +cannot complete its interaction with the resource and release +that resource. The high priority task is effectively prevented +from executing by lower priority tasks. + + +Priority Inheritance +-------------------- + +Priority inheritance is an algorithm that calls for +the lower priority task holding a resource to have its priority +increased to that of the highest priority task blocked waiting +for that resource. Each time a task blocks attempting to obtain +the resource, the task holding the resource may have its +priority increased. + +On SMP configurations, in case the task holding the resource and the task that +blocks attempting to obtain the resource are in different scheduler instances, +the priority of the holder is raised to the pseudo-interrupt priority (priority +boosting). The pseudo-interrupt priority is the highest priority. + +RTEMS supports priority inheritance for local, binary +semaphores that use the priority task wait queue blocking +discipline. When a task of higher priority than the task +holding the semaphore blocks, the priority of the task holding +the semaphore is increased to that of the blocking task. When +the task holding the task completely releases the binary +semaphore (i.e. not for a nested release), the holder’s priority +is restored to the value it had before any higher priority was +inherited. + +The RTEMS implementation of the priority inheritance +algorithm takes into account the scenario in which a task holds +more than one binary semaphore. The holding task will execute +at the priority of the higher of the highest ceiling priority or +at the priority of the highest priority task blocked waiting for +any of the semaphores the task holds. Only when the task +releases ALL of the binary semaphores it holds will its priority +be restored to the normal value. + +Priority Ceiling +---------------- + +Priority ceiling is an algorithm that calls for the +lower priority task holding a resource to have its priority +increased to that of the highest priority task which will EVER +block waiting for that resource. This algorithm addresses the +problem of priority inversion although it avoids the possibility +of changing the priority of the task holding the resource +multiple times. The priority ceiling algorithm will only change +the priority of the task holding the resource a maximum of one +time. The ceiling priority is set at creation time and must be +the priority of the highest priority task which will ever +attempt to acquire that semaphore. + +RTEMS supports priority ceiling for local, binary +semaphores that use the priority task wait queue blocking +discipline. When a task of lower priority than the ceiling +priority successfully obtains the semaphore, its priority is +raised to the ceiling priority. When the task holding the task +completely releases the binary semaphore (i.e. not for a nested +release), the holder’s priority is restored to the value it had +before any higher priority was put into effect. + +The need to identify the highest priority task which +will attempt to obtain a particular semaphore can be a difficult +task in a large, complicated system. Although the priority +ceiling algorithm is more efficient than the priority +inheritance algorithm with respect to the maximum number of task +priority changes which may occur while a task holds a particular +semaphore, the priority inheritance algorithm is more forgiving +in that it does not require this apriori information. + +The RTEMS implementation of the priority ceiling +algorithm takes into account the scenario in which a task holds +more than one binary semaphore. The holding task will execute +at the priority of the higher of the highest ceiling priority or +at the priority of the highest priority task blocked waiting for +any of the semaphores the task holds. Only when the task +releases ALL of the binary semaphores it holds will its priority +be restored to the normal value. + + +Multiprocessor Resource Sharing Protocol +---------------------------------------- + +The Multiprocessor Resource Sharing Protocol (MrsP) is defined in *A. +Burns and A.J. Wellings, A Schedulability Compatible Multiprocessor Resource +Sharing Protocol - MrsP, Proceedings of the 25th Euromicro Conference on +Real-Time Systems (ECRTS 2013), July 2013*. It is a generalization of the +Priority Ceiling Protocol to SMP systems. Each MrsP semaphore uses a ceiling +priority per scheduler instance. These ceiling priorities can be specified +with ``rtems_semaphore_set_priority()``. A task obtaining or owning a MrsP +semaphore will execute with the ceiling priority for its scheduler instance as +specified by the MrsP semaphore object. Tasks waiting to get ownership of a +MrsP semaphore will not relinquish the processor voluntarily. In case the +owner of a MrsP semaphore gets preempted it can ask all tasks waiting for this +semaphore to help out and temporarily borrow the right to execute on one of +their assigned processors. + +Building a Semaphore Attribute Set +---------------------------------- + +In general, an attribute set is built by a bitwise OR +of the desired attribute components. The following table lists +the set of valid semaphore attributes: + +- ``RTEMS_FIFO`` - tasks wait by FIFO (default) + +- ``RTEMS_PRIORITY`` - tasks wait by priority + +- ``RTEMS_BINARY_SEMAPHORE`` - restrict values to + 0 and 1 + +- ``RTEMS_COUNTING_SEMAPHORE`` - no restriction on values + (default) + +- ``RTEMS_SIMPLE_BINARY_SEMAPHORE`` - restrict values to + 0 and 1, do not allow nested access, allow deletion of locked semaphore. + +- ``RTEMS_NO_INHERIT_PRIORITY`` - do not use priority + inheritance (default) + +- ``RTEMS_INHERIT_PRIORITY`` - use priority inheritance + +- ``RTEMS_NO_PRIORITY_CEILING`` - do not use priority + ceiling (default) + +- ``RTEMS_PRIORITY_CEILING`` - use priority ceiling + +- ``RTEMS_NO_MULTIPROCESSOR_RESOURCE_SHARING`` - do not use + Multiprocessor Resource Sharing Protocol (default) + +- ``RTEMS_MULTIPROCESSOR_RESOURCE_SHARING`` - use + Multiprocessor Resource Sharing Protocol + +- ``RTEMS_LOCAL`` - local semaphore (default) + +- ``RTEMS_GLOBAL`` - global semaphore + +Attribute values are specifically designed to be +mutually exclusive, therefore bitwise OR and addition operations +are equivalent as long as each attribute appears exactly once in +the component list. An attribute listed as a default is not +required to appear in the attribute list, although it is a good +programming practice to specify default attributes. If all +defaults are desired, the attribute``RTEMS_DEFAULT_ATTRIBUTES`` should be +specified on this call. + +This example demonstrates the attribute_set parameter needed to create a +local semaphore with the task priority waiting queue discipline. The +attribute_set parameter passed to the``rtems_semaphore_create`` directive could be either``RTEMS_PRIORITY`` or ``RTEMS_LOCAL | +RTEMS_PRIORITY``. The attribute_set parameter can be set to``RTEMS_PRIORITY`` because ``RTEMS_LOCAL`` is the +default for all created tasks. If a similar semaphore were to be known +globally, then the attribute_set parameter would be``RTEMS_GLOBAL | RTEMS_PRIORITY``. + +Some combinatinos of these attributes are invalid. For example, priority +ordered blocking discipline must be applied to a binary semaphore in order +to use either the priority inheritance or priority ceiling functionality. +The following tree figure illustrates the valid combinations. + +.. code:: c + + Not available in ASCII representation + +Building a SEMAPHORE_OBTAIN Option Set +-------------------------------------- + +In general, an option is built by a bitwise OR of the +desired option components. The set of valid options for the``rtems_semaphore_obtain`` directive are listed +in the following table: + +- ``RTEMS_WAIT`` - task will wait for semaphore (default) + +- ``RTEMS_NO_WAIT`` - task should not wait + +Option values are specifically designed to be mutually exclusive, +therefore bitwise OR and addition operations are equivalent as long as +each attribute appears exactly once in the component list. An option +listed as a default is not required to appear in the list, although it is +a good programming practice to specify default options. If all defaults +are desired, the option ``RTEMS_DEFAULT_OPTIONS`` should be +specified on this call. + +This example demonstrates the option parameter needed +to poll for a semaphore. The option parameter passed to the``rtems_semaphore_obtain`` +directive should be ``RTEMS_NO_WAIT``. + +Operations +========== + +Creating a Semaphore +-------------------- + +The ``rtems_semaphore_create`` directive creates a binary or +counting semaphore with a user-specified name as well as an +initial count. If a binary semaphore is created with a count of +zero (0) to indicate that it has been allocated, then the task +creating the semaphore is considered the current holder of the +semaphore. At create time the method for ordering waiting tasks +in the semaphore’s task wait queue (by FIFO or task priority) is +specified. Additionally, the priority inheritance or priority +ceiling algorithm may be selected for local, binary semaphores +that use the priority task wait queue blocking discipline. If +the priority ceiling algorithm is selected, then the highest +priority of any task which will attempt to obtain this semaphore +must be specified. RTEMS allocates a Semaphore Control Block +(SMCB) from the SMCB free list. This data structure is used by +RTEMS to manage the newly created semaphore. Also, a unique +semaphore ID is generated and returned to the calling task. + +Obtaining Semaphore IDs +----------------------- + +When a semaphore is created, RTEMS generates a unique +semaphore ID and assigns it to the created semaphore until it is +deleted. The semaphore ID may be obtained by either of two +methods. First, as the result of an invocation of the``rtems_semaphore_create`` directive, the +semaphore ID is stored in a user provided location. Second, +the semaphore ID may be obtained later using the``rtems_semaphore_ident`` directive. The semaphore ID is +used by other semaphore manager directives to access this +semaphore. + +Acquiring a Semaphore +--------------------- + +The ``rtems_semaphore_obtain`` directive is used to acquire the +specified semaphore. A simplified version of the``rtems_semaphore_obtain`` directive can be described as follows: +.. code:: c + + if semaphore's count is greater than zero + then decrement semaphore's count + else wait for release of semaphore + return SUCCESSFUL + +When the semaphore cannot be immediately acquired, +one of the following situations applies: + +- By default, the calling task will wait forever to + acquire the semaphore. + +- Specifying ``RTEMS_NO_WAIT`` forces an immediate return + with an error status code. + +- Specifying a timeout limits the interval the task will + wait before returning with an error status code. + +If the task waits to acquire the semaphore, then it +is placed in the semaphore’s task wait queue in either FIFO or +task priority order. If the task blocked waiting for a binary +semaphore using priority inheritance and the task’s priority is +greater than that of the task currently holding the semaphore, +then the holding task will inherit the priority of the blocking +task. All tasks waiting on a semaphore are returned an error +code when the semaphore is deleted. + +When a task successfully obtains a semaphore using +priority ceiling and the priority ceiling for this semaphore is +greater than that of the holder, then the holder’s priority will +be elevated. + +Releasing a Semaphore +--------------------- + +The ``rtems_semaphore_release`` directive is used to release +the specified semaphore. A simplified version of the``rtems_semaphore_release`` directive can be described as +follows: +.. code:: c + + if no tasks are waiting on this semaphore + then increment semaphore's count + else assign semaphore to a waiting task + return SUCCESSFUL + +If this is the outermost release of a binary +semaphore that uses priority inheritance or priority ceiling and +the task does not currently hold any other binary semaphores, +then the task performing the ``rtems_semaphore_release`` +will have its priority restored to its normal value. + +Deleting a Semaphore +-------------------- + +The ``rtems_semaphore_delete`` directive removes a semaphore +from the system and frees its control block. A semaphore can be +deleted by any local task that knows the semaphore’s ID. As a +result of this directive, all tasks blocked waiting to acquire +the semaphore will be readied and returned a status code which +indicates that the semaphore was deleted. Any subsequent +references to the semaphore’s name and ID are invalid. + +Directives +========== + +This section details the semaphore manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +SEMAPHORE_CREATE - Create a semaphore +------------------------------------- +.. index:: create a semaphore + +**CALLING SEQUENCE:** + +.. index:: rtems_semaphore_create + +.. code:: c + + rtems_status_code rtems_semaphore_create( + rtems_name name, + uint32_t count, + rtems_attribute attribute_set, + rtems_task_priority priority_ceiling, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - semaphore created successfully +``RTEMS_INVALID_NAME`` - invalid semaphore name +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_TOO_MANY`` - too many semaphores created +``RTEMS_NOT_DEFINED`` - invalid attribute set +``RTEMS_INVALID_NUMBER`` - invalid starting count for binary semaphore +``RTEMS_MP_NOT_CONFIGURED`` - multiprocessing not configured +``RTEMS_TOO_MANY`` - too many global objects + +**DESCRIPTION:** + +This directive creates a semaphore which resides on +the local node. The created semaphore has the user-defined name +specified in name and the initial count specified in count. For +control and maintenance of the semaphore, RTEMS allocates and +initializes a SMCB. The RTEMS-assigned semaphore id is returned +in id. This semaphore id is used with other semaphore related +directives to access the semaphore. + +Specifying PRIORITY in attribute_set causes tasks +waiting for a semaphore to be serviced according to task +priority. When FIFO is selected, tasks are serviced in First +In-First Out order. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +The priority inheritance and priority ceiling +algorithms are only supported for local, binary semaphores that +use the priority task wait queue blocking discipline. + +The following semaphore attribute constants are +defined by RTEMS: + +- ``RTEMS_FIFO`` - tasks wait by FIFO (default) + +- ``RTEMS_PRIORITY`` - tasks wait by priority + +- ``RTEMS_BINARY_SEMAPHORE`` - restrict values to + 0 and 1 + +- ``RTEMS_COUNTING_SEMAPHORE`` - no restriction on values + (default) + +- ``RTEMS_SIMPLE_BINARY_SEMAPHORE`` - restrict values to + 0 and 1, block on nested access, allow deletion of locked semaphore. + +- ``RTEMS_NO_INHERIT_PRIORITY`` - do not use priority + inheritance (default) + +- ``RTEMS_INHERIT_PRIORITY`` - use priority inheritance + +- ``RTEMS_NO_PRIORITY_CEILING`` - do not use priority + ceiling (default) + +- ``RTEMS_PRIORITY_CEILING`` - use priority ceiling + +- ``RTEMS_NO_MULTIPROCESSOR_RESOURCE_SHARING`` - do not use + Multiprocessor Resource Sharing Protocol (default) + +- ``RTEMS_MULTIPROCESSOR_RESOURCE_SHARING`` - use + Multiprocessor Resource Sharing Protocol + +- ``RTEMS_LOCAL`` - local semaphore (default) + +- ``RTEMS_GLOBAL`` - global semaphore + +Semaphores should not be made global unless remote +tasks must interact with the created semaphore. This is to +avoid the system overhead incurred by the creation of a global +semaphore. When a global semaphore is created, the semaphore’s +name and id must be transmitted to every node in the system for +insertion in the local copy of the global object table. + +Note that some combinations of attributes are not valid. See the +earlier discussion on this. + +The total number of global objects, including semaphores, is limited by +the maximum_global_objects field in the Configuration Table. + +It is not allowed to create an initially locked MrsP semaphore and the``RTEMS_INVALID_NUMBER`` status code will be returned on SMP +configurations in this case. This prevents lock order reversal problems with +the allocator mutex. + +SEMAPHORE_IDENT - Get ID of a semaphore +--------------------------------------- +.. index:: get ID of a semaphore +.. index:: obtain ID of a semaphore + +**CALLING SEQUENCE:** + +.. index:: rtems_semaphore_ident + +.. code:: c + + rtems_status_code rtems_semaphore_ident( + rtems_name name, + uint32_t node, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - semaphore identified successfully +``RTEMS_INVALID_NAME`` - semaphore name not found +``RTEMS_INVALID_NODE`` - invalid node id + +**DESCRIPTION:** + +This directive obtains the semaphore id associated +with the semaphore name. If the semaphore name is not unique, +then the semaphore id will match one of the semaphores with that +name. However, this semaphore id is not guaranteed to +correspond to the desired semaphore. The semaphore id is used +by other semaphore related directives to access the semaphore. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +If node is ``RTEMS_SEARCH_ALL_NODES``, all nodes are searched +with the local node being searched first. All other nodes are +searched with the lowest numbered node searched first. + +If node is a valid node number which does not +represent the local node, then only the semaphores exported by +the designated node are searched. + +This directive does not generate activity on remote +nodes. It accesses only the local copy of the global object +table. + +SEMAPHORE_DELETE - Delete a semaphore +------------------------------------- +.. index:: delete a semaphore + +**CALLING SEQUENCE:** + +.. index:: rtems_semaphore_delete + +.. code:: c + + rtems_status_code rtems_semaphore_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - semaphore deleted successfully +``RTEMS_INVALID_ID`` - invalid semaphore id +``RTEMS_RESOURCE_IN_USE`` - binary semaphore is in use +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - cannot delete remote semaphore + +**DESCRIPTION:** + +This directive deletes the semaphore specified by ``id``. +All tasks blocked waiting to acquire the semaphore will be +readied and returned a status code which indicates that the +semaphore was deleted. The SMCB for this semaphore is reclaimed +by RTEMS. + +**NOTES:** + +The calling task will be preempted if it is enabled +by the task’s execution mode and a higher priority local task is +waiting on the deleted semaphore. The calling task will NOT be +preempted if all of the tasks that are waiting on the semaphore +are remote tasks. + +The calling task does not have to be the task that +created the semaphore. Any local task that knows the semaphore +id can delete the semaphore. + +When a global semaphore is deleted, the semaphore id +must be transmitted to every node in the system for deletion +from the local copy of the global object table. + +The semaphore must reside on the local node, even if +the semaphore was created with the ``RTEMS_GLOBAL`` option. + +Proxies, used to represent remote tasks, are +reclaimed when the semaphore is deleted. + +SEMAPHORE_OBTAIN - Acquire a semaphore +-------------------------------------- +.. index:: obtain a semaphore +.. index:: lock a semaphore + +**CALLING SEQUENCE:** + +.. index:: rtems_semaphore_obtain + +.. code:: c + + rtems_status_code rtems_semaphore_obtain( + rtems_id id, + rtems_option option_set, + rtems_interval timeout + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - semaphore obtained successfully +``RTEMS_UNSATISFIED`` - semaphore not available +``RTEMS_TIMEOUT`` - timed out waiting for semaphore +``RTEMS_OBJECT_WAS_DELETED`` - semaphore deleted while waiting +``RTEMS_INVALID_ID`` - invalid semaphore id + +**DESCRIPTION:** + +This directive acquires the semaphore specified by +id. The ``RTEMS_WAIT`` and ``RTEMS_NO_WAIT`` components of the options parameter +indicate whether the calling task wants to wait for the +semaphore to become available or return immediately if the +semaphore is not currently available. With either ``RTEMS_WAIT`` or``RTEMS_NO_WAIT``, if the current semaphore count is positive, then it is +decremented by one and the semaphore is successfully acquired by +returning immediately with a successful return code. + +If the calling task chooses to return immediately and the current +semaphore count is zero or negative, then a status code is returned +indicating that the semaphore is not available. If the calling task +chooses to wait for a semaphore and the current semaphore count is zero or +negative, then it is decremented by one and the calling task is placed on +the semaphore’s wait queue and blocked. If the semaphore was created with +the ``RTEMS_PRIORITY`` attribute, then the calling task is +inserted into the queue according to its priority. However, if the +semaphore was created with the ``RTEMS_FIFO`` attribute, then +the calling task is placed at the rear of the wait queue. If the binary +semaphore was created with the ``RTEMS_INHERIT_PRIORITY`` +attribute, then the priority of the task currently holding the binary +semaphore is guaranteed to be greater than or equal to that of the +blocking task. If the binary semaphore was created with the``RTEMS_PRIORITY_CEILING`` attribute, a task successfully +obtains the semaphore, and the priority of that task is greater than the +ceiling priority for this semaphore, then the priority of the task +obtaining the semaphore is elevated to that of the ceiling. + +The timeout parameter specifies the maximum interval the calling task is +willing to be blocked waiting for the semaphore. If it is set to``RTEMS_NO_TIMEOUT``, then the calling task will wait forever. +If the semaphore is available or the ``RTEMS_NO_WAIT`` option +component is set, then timeout is ignored. + +Deadlock situations are detected for MrsP semaphores and the``RTEMS_UNSATISFIED`` status code will be returned on SMP +configurations in this case. + +**NOTES:** + +The following semaphore acquisition option constants +are defined by RTEMS: + +- ``RTEMS_WAIT`` - task will wait for semaphore (default) + +- ``RTEMS_NO_WAIT`` - task should not wait + +Attempting to obtain a global semaphore which does not reside on the local +node will generate a request to the remote node to access the semaphore. +If the semaphore is not available and ``RTEMS_NO_WAIT`` was +not specified, then the task must be blocked until the semaphore is +released. A proxy is allocated on the remote node to represent the task +until the semaphore is released. + +A clock tick is required to support the timeout functionality of +this directive. + +It is not allowed to obtain a MrsP semaphore more than once by one task at a +time (nested access) and the ``RTEMS_UNSATISFIED`` status code will +be returned on SMP configurations in this case. + +SEMAPHORE_RELEASE - Release a semaphore +--------------------------------------- +.. index:: release a semaphore +.. index:: unlock a semaphore + +**CALLING SEQUENCE:** + +.. index:: rtems_semaphore_release + +.. code:: c + + rtems_status_code rtems_semaphore_release( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - semaphore released successfully +``RTEMS_INVALID_ID`` - invalid semaphore id +``RTEMS_NOT_OWNER_OF_RESOURCE`` - calling task does not own semaphore +``RTEMS_INCORRECT_STATE`` - invalid unlock order + +**DESCRIPTION:** + +This directive releases the semaphore specified by +id. The semaphore count is incremented by one. If the count is +zero or negative, then the first task on this semaphore’s wait +queue is removed and unblocked. The unblocked task may preempt +the running task if the running task’s preemption mode is +enabled and the unblocked task has a higher priority than the +running task. + +**NOTES:** + +The calling task may be preempted if it causes a +higher priority task to be made ready for execution. + +Releasing a global semaphore which does not reside on +the local node will generate a request telling the remote node +to release the semaphore. + +If the task to be unblocked resides on a different +node from the semaphore, then the semaphore allocation is +forwarded to the appropriate node, the waiting task is +unblocked, and the proxy used to represent the task is reclaimed. + +The outermost release of a local, binary, priority +inheritance or priority ceiling semaphore may result in the +calling task having its priority lowered. This will occur if +the calling task holds no other binary semaphores and it has +inherited a higher priority. + +The MrsP semaphores must be released in the reversed obtain order, otherwise +the ``RTEMS_INCORRECT_STATE`` status code will be returned on SMP +configurations in this case. + +SEMAPHORE_FLUSH - Unblock all tasks waiting on a semaphore +---------------------------------------------------------- +.. index:: flush a semaphore +.. index:: unblock all tasks waiting on a semaphore + +**CALLING SEQUENCE:** + +.. index:: rtems_semaphore_flush + +.. code:: c + + rtems_status_code rtems_semaphore_flush( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - semaphore released successfully +``RTEMS_INVALID_ID`` - invalid semaphore id +``RTEMS_NOT_DEFINED`` - operation not defined for the protocol of +the semaphore +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - not supported for remote semaphores + +**DESCRIPTION:** + +This directive unblocks all tasks waiting on the semaphore specified by +id. Since there are tasks blocked on the semaphore, the semaphore’s +count is not changed by this directive and thus is zero before and +after this directive is executed. Tasks which are unblocked as the +result of this directive will return from the``rtems_semaphore_obtain`` directive with a +status code of ``RTEMS_UNSATISFIED`` to indicate +that the semaphore was not obtained. + +This directive may unblock any number of tasks. Any of the unblocked +tasks may preempt the running task if the running task’s preemption mode is +enabled and an unblocked task has a higher priority than the +running task. + +**NOTES:** + +The calling task may be preempted if it causes a +higher priority task to be made ready for execution. + +If the task to be unblocked resides on a different +node from the semaphore, then the waiting task is +unblocked, and the proxy used to represent the task is reclaimed. + +It is not allowed to flush a MrsP semaphore and the``RTEMS_NOT_DEFINED`` status code will be returned on SMP +configurations in this case. + +SEMAPHORE_SET_PRIORITY - Set priority by scheduler for a semaphore +------------------------------------------------------------------ +.. index:: set priority by scheduler for a semaphore + +**CALLING SEQUENCE:** + +.. index:: rtems_semaphore_set_priority + +.. code:: c + + rtems_status_code rtems_semaphore_set_priority( + rtems_id semaphore_id, + rtems_id scheduler_id, + rtems_task_priority new_priority, + rtems_task_priority \*old_priority + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successful operation +``RTEMS_INVALID_ID`` - invalid semaphore or scheduler id +``RTEMS_INVALID_ADDRESS`` - ``old_priority`` is NULL +``RTEMS_INVALID_PRIORITY`` - invalid new priority value +``RTEMS_NOT_DEFINED`` - operation not defined for the protocol of +the semaphore +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - not supported for remote semaphores + +**DESCRIPTION:** + +This directive sets the priority value with respect to the specified scheduler +of a semaphore. + +The special priority value ``RTEMS_CURRENT_PRIORITY`` can be used to get the +current priority value without changing it. + +The interpretation of the priority value depends on the protocol of the +semaphore object. + +- The Multiprocessor Resource Sharing Protocol needs a ceiling priority per + scheduler instance. This operation can be used to specify these priority + values. + +- For the Priority Ceiling Protocol the ceiling priority is used with this + operation. + +- For other protocols this operation is not defined. + +**EXAMPLE:** + +.. code:: c + + #include + #include + #include + #define SCHED_A rtems_build_name(' ', ' ', ' ', 'A') + #define SCHED_B rtems_build_name(' ', ' ', ' ', 'B') + static void Init(rtems_task_argument arg) + { + rtems_status_code sc; + rtems_id semaphore_id; + rtems_id scheduler_a_id; + rtems_id scheduler_b_id; + rtems_task_priority prio; + /* Get the scheduler identifiers \*/ + sc = rtems_scheduler_ident(SCHED_A, &scheduler_a_id); + assert(sc == RTEMS_SUCCESSFUL); + sc = rtems_scheduler_ident(SCHED_B, &scheduler_b_id); + assert(sc == RTEMS_SUCCESSFUL); + /* Create a MrsP semaphore object \*/ + sc = rtems_semaphore_create( + rtems_build_name('M', 'R', 'S', 'P'), + 1, + RTEMS_MULTIPROCESSOR_RESOURCE_SHARING + | RTEMS_BINARY_SEMAPHORE, + 1, + &semaphore_id + ); + assert(sc == RTEMS_SUCCESSFUL); + /* + * The ceiling priority values per scheduler are equal to the value specified + * for object creation. + \*/ + prio = RTEMS_CURRENT_PRIORITY; + sc = rtems_semaphore_set_priority(semaphore_id, scheduler_a_id, prio, &prio); + assert(sc == RTEMS_SUCCESSFUL); + assert(prio == 1); + /* Check the old value and set a new ceiling priority for scheduler B \*/ + prio = 2; + sc = rtems_semaphore_set_priority(semaphore_id, scheduler_b_id, prio, &prio); + assert(sc == RTEMS_SUCCESSFUL); + assert(prio == 1); + /* Check the ceiling priority values \*/ + prio = RTEMS_CURRENT_PRIORITY; + sc = rtems_semaphore_set_priority(semaphore_id, scheduler_a_id, prio, &prio); + assert(sc == RTEMS_SUCCESSFUL); + assert(prio == 1); + prio = RTEMS_CURRENT_PRIORITY; + sc = rtems_semaphore_set_priority(semaphore_id, scheduler_b_id, prio, &prio); + assert(sc == RTEMS_SUCCESSFUL); + assert(prio == 2); + sc = rtems_semaphore_delete(semaphore_id); + assert(sc == RTEMS_SUCCESSFUL); + exit(0); + } + #define CONFIGURE_SMP_APPLICATION + #define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER + #define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER + #define CONFIGURE_MAXIMUM_TASKS 1 + #define CONFIGURE_MAXIMUM_SEMAPHORES 1 + #define CONFIGURE_MAXIMUM_MRSP_SEMAPHORES 1 + #define CONFIGURE_SMP_MAXIMUM_PROCESSORS 2 + #define CONFIGURE_SCHEDULER_SIMPLE_SMP + #include + RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP(a); + RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP(b); + #define CONFIGURE_SCHEDULER_CONTROLS \\ + RTEMS_SCHEDULER_CONTROL_SIMPLE_SMP(a, SCHED_A), \\ + RTEMS_SCHEDULER_CONTROL_SIMPLE_SMP(b, SCHED_B) + #define CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS \\ + RTEMS_SCHEDULER_ASSIGN(0, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \\ + RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY) + #define CONFIGURE_RTEMS_INIT_TASKS_TABLE + #define CONFIGURE_INIT + #include + +.. COMMENT: COPYRIGHT (c) 1988-2007. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Barrier Manager +############### + +.. index:: barrier + +Introduction +============ + +The barrier manager provides a unique synchronization +capability which can be used to have a set of tasks block +and be unblocked as a set. The directives provided by the +barrier manager are: + +- ``rtems_barrier_create`` - Create a barrier + +- ``rtems_barrier_ident`` - Get ID of a barrier + +- ``rtems_barrier_delete`` - Delete a barrier + +- ``rtems_barrier_wait`` - Wait at a barrier + +- ``rtems_barrier_release`` - Release a barrier + +Background +========== + +A barrier can be viewed as a gate at which tasks wait until +the gate is opened. This has many analogies in the real world. +Horses and other farm animals may approach a closed gate and +gather in front of it, waiting for someone to open the gate so +they may proceed. Similarly, cticket holders gather at the gates +of arenas before concerts or sporting events waiting for the +arena personnel to open the gates so they may enter. + +Barriers are useful during application initialization. Each +application task can perform its local initialization before +waiting for the application as a whole to be initialized. Once +all tasks have completed their independent initializations, +the "application ready" barrier can be released. + +Automatic Versus Manual Barriers +-------------------------------- + +Just as with a real-world gate, barriers may be configured to +be manually opened or automatically opened. All tasks +calling the ``rtems_barrier_wait`` directive +will block until a controlling task invokes the``rtems_barrier_release`` directive. + +Automatic barriers are created with a limit to the number of +tasks which may simultaneously block at the barrier. Once +this limit is reached, all of the tasks are released. For +example, if the automatic limit is ten tasks, then the first +nine tasks calling the ``rtems_barrier_wait`` directive +will block. When the tenth task calls the``rtems_barrier_wait`` directive, the nine +blocked tasks will be released and the tenth task returns +to the caller without blocking. + +Building a Barrier Attribute Set +-------------------------------- + +In general, an attribute set is built by a bitwise OR +of the desired attribute components. The following table lists +the set of valid barrier attributes: + +- ``RTEMS_BARRIER_AUTOMATIC_RELEASE`` - automatically + release the barrier when the configured number of tasks are blocked + +- ``RTEMS_BARRIER_MANUAL_RELEASE`` - only release + the barrier when the application invokes the``rtems_barrier_release`` directive. (default) + +*NOTE*: Barriers only support FIFO blocking order because all +waiting tasks are released as a set. Thus the released tasks +will all become ready to execute at the same time and compete +for the processor based upon their priority. + +Attribute values are specifically designed to be +mutually exclusive, therefore bitwise OR and addition operations +are equivalent as long as each attribute appears exactly once in +the component list. An attribute listed as a default is not +required to appear in the attribute list, although it is a good +programming practice to specify default attributes. If all +defaults are desired, the attribute``RTEMS_DEFAULT_ATTRIBUTES`` should be +specified on this call. + +This example demonstrates the attribute_set parameter needed to create a +barrier with the automatic release policy. The``attribute_set`` parameter passed to the``rtems_barrier_create`` directive will be``RTEMS_BARRIER_AUTOMATIC_RELEASE``. In this case, the +user must also specify the *maximum_waiters* parameter. + +Operations +========== + +Creating a Barrier +------------------ + +The ``rtems_barrier_create`` directive creates +a barrier with a user-specified name and the desired attributes. +RTEMS allocates a Barrier Control Block (BCB) from the BCB free list. +This data structure is used by RTEMS to manage the newly created +barrier. Also, a unique barrier ID is generated and returned to +the calling task. + +Obtaining Barrier IDs +--------------------- + +When a barrier is created, RTEMS generates a unique +barrier ID and assigns it to the created barrier until it is +deleted. The barrier ID may be obtained by either of two +methods. First, as the result of an invocation of the``rtems_barrier_create`` directive, the +barrier ID is stored in a user provided location. Second, +the barrier ID may be obtained later using the``rtems_barrier_ident`` directive. The barrier ID is +used by other barrier manager directives to access this +barrier. + +Waiting at a Barrier +-------------------- + +The ``rtems_barrier_wait`` directive is used to wait at +the specified barrier. Since a barrier is, by definition, never immediately, +the task may wait forever for the barrier to be released or it may +specify a timeout. Specifying a timeout limits the interval the task will +wait before returning with an error status code. + +If the barrier is configured as automatic and there are already +one less then the maximum number of waiters, then the call will +unblock all tasks waiting at the barrier and the caller will +return immediately. + +When the task does wait to acquire the barrier, then it +is placed in the barrier’s task wait queue in FIFO order. +All tasks waiting on a barrier are returned an error +code when the barrier is deleted. + +Releasing a Barrier +------------------- + +The ``rtems_barrier_release`` directive is used to release +the specified barrier. When the ``rtems_barrier_release`` +is invoked, all tasks waiting at the barrier are immediately made ready +to execute and begin to compete for the processor to execute. + +Deleting a Barrier +------------------ + +The ``rtems_barrier_delete`` directive removes a barrier +from the system and frees its control block. A barrier can be +deleted by any local task that knows the barrier’s ID. As a +result of this directive, all tasks blocked waiting for the +barrier to be released, will be readied and returned a status code which +indicates that the barrier was deleted. Any subsequent +references to the barrier’s name and ID are invalid. + +Directives +========== + +This section details the barrier manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +BARRIER_CREATE - Create a barrier +--------------------------------- +.. index:: create a barrier + +**CALLING SEQUENCE:** + +.. index:: rtems_barrier_create + +.. code:: c + + rtems_status_code rtems_barrier_create( + rtems_name name, + rtems_attribute attribute_set, + uint32_t maximum_waiters, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - barrier created successfully +``RTEMS_INVALID_NAME`` - invalid barrier name +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_TOO_MANY`` - too many barriers created  + +**DESCRIPTION:** + +This directive creates a barrier which resides on +the local node. The created barrier has the user-defined name +specified in ``name`` and the initial count specified in ``count``. For +control and maintenance of the barrier, RTEMS allocates and +initializes a BCB. The RTEMS-assigned barrier id is returned +in ``id``. This barrier id is used with other barrier related +directives to access the barrier. + +``RTEMS_BARRIER_MANUAL_RELEASE`` - only release + +Specifying ``RTEMS_BARRIER_AUTOMATIC_RELEASE`` in``attribute_set`` causes tasks calling the``rtems_barrier_wait`` directive to block until +there are ``maximum_waiters - 1`` tasks waiting at the barrier. +When the ``maximum_waiters`` task invokes the``rtems_barrier_wait`` directive, the previous``maximum_waiters - 1`` tasks are automatically released +and the caller returns. + +In contrast, when the ``RTEMS_BARRIER_MANUAL_RELEASE`` +attribute is specified, there is no limit on the number of +tasks that will block at the barrier. Only when the``rtems_barrier_release`` directive is invoked, +are the tasks waiting at the barrier unblocked. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +The following barrier attribute constants are defined by RTEMS: + +- ``RTEMS_BARRIER_AUTOMATIC_RELEASE`` - automatically + release the barrier when the configured number of tasks are blocked + +- ``RTEMS_BARRIER_MANUAL_RELEASE`` - only release + the barrier when the application invokes the``rtems_barrier_release`` directive. (default) + +BARRIER_IDENT - Get ID of a barrier +----------------------------------- +.. index:: get ID of a barrier +.. index:: obtain ID of a barrier + +**CALLING SEQUENCE:** + +.. index:: rtems_barrier_ident + +.. code:: c + + rtems_status_code rtems_barrier_ident( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - barrier identified successfully +``RTEMS_INVALID_NAME`` - barrier name not found +``RTEMS_INVALID_NODE`` - invalid node id + +**DESCRIPTION:** + +This directive obtains the barrier id associated +with the barrier name. If the barrier name is not unique, +then the barrier id will match one of the barriers with that +name. However, this barrier id is not guaranteed to +correspond to the desired barrier. The barrier id is used +by other barrier related directives to access the barrier. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +BARRIER_DELETE - Delete a barrier +--------------------------------- +.. index:: delete a barrier + +**CALLING SEQUENCE:** + +.. index:: rtems_barrier_delete + +.. code:: c + + rtems_status_code rtems_barrier_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - barrier deleted successfully +``RTEMS_INVALID_ID`` - invalid barrier id  + +**DESCRIPTION:** + +This directive deletes the barrier specified by ``id``. +All tasks blocked waiting for the barrier to be released will be +readied and returned a status code which indicates that the +barrier was deleted. The BCB for this barrier is reclaimed +by RTEMS. + +**NOTES:** + +The calling task will be preempted if it is enabled +by the task’s execution mode and a higher priority local task is +waiting on the deleted barrier. The calling task will NOT be +preempted if all of the tasks that are waiting on the barrier +are remote tasks. + +The calling task does not have to be the task that +created the barrier. Any local task that knows the barrier +id can delete the barrier. + +.. COMMENT: Barrier Obtain + +BARRIER_OBTAIN - Acquire a barrier +---------------------------------- +.. index:: obtain a barrier +.. index:: lock a barrier + +**CALLING SEQUENCE:** + +.. index:: rtems_barrier_wait + +.. code:: c + + rtems_status_code rtems_barrier_wait( + rtems_id id, + rtems_interval timeout + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - barrier released and task unblocked +``RTEMS_UNSATISFIED`` - barrier not available +``RTEMS_TIMEOUT`` - timed out waiting for barrier +``RTEMS_OBJECT_WAS_DELETED`` - barrier deleted while waiting +``RTEMS_INVALID_ID`` - invalid barrier id + +**DESCRIPTION:** + +This directive acquires the barrier specified by +id. The ``RTEMS_WAIT`` and ``RTEMS_NO_WAIT`` +components of the options parameter indicate whether the calling task +wants to wait for the barrier to become available or return immediately +if the barrier is not currently available. With either``RTEMS_WAIT`` or ``RTEMS_NO_WAIT``, +if the current barrier count is positive, then it is +decremented by one and the barrier is successfully acquired by +returning immediately with a successful return code. + +Conceptually, the calling task should always be thought +of as blocking when it makes this call and being unblocked when +the barrier is released. If the barrier is configured for +manual release, this rule of thumb will always be valid. +If the barrier is configured for automatic release, all callers +will block except for the one which is the Nth task which trips +the automatic release condition. + +The timeout parameter specifies the maximum interval the calling task is +willing to be blocked waiting for the barrier. If it is set to``RTEMS_NO_TIMEOUT``, then the calling task will wait forever. +If the barrier is available or the ``RTEMS_NO_WAIT`` option +component is set, then timeout is ignored. + +**NOTES:** + +The following barrier acquisition option constants are defined by RTEMS: + +- ``RTEMS_WAIT`` - task will wait for barrier (default) + +- ``RTEMS_NO_WAIT`` - task should not wait + +A clock tick is required to support the timeout functionality of +this directive. + +.. COMMENT: Release Barrier + +BARRIER_RELEASE - Release a barrier +----------------------------------- +.. index:: wait at a barrier +.. index:: release a barrier + +**CALLING SEQUENCE:** + +.. index:: rtems_barrier_release + +.. code:: c + + rtems_status_code rtems_barrier_release( + rtems_id id, + uint32_t \*released + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - barrier released successfully +``RTEMS_INVALID_ID`` - invalid barrier id + +**DESCRIPTION:** + +This directive releases the barrier specified by id. +All tasks waiting at the barrier will be unblocked. +If the running task’s preemption mode is enabled and one of +the unblocked tasks has a higher priority than the running task. + +**NOTES:** + +The calling task may be preempted if it causes a +higher priority task to be made ready for execution. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Message Manager +############### + +.. index:: messages +.. index:: message queues + +Introduction +============ + +The message manager provides communication and +synchronization capabilities using RTEMS message queues. The +directives provided by the message manager are: + +- ``rtems_message_queue_create`` - Create a queue + +- ``rtems_message_queue_ident`` - Get ID of a queue + +- ``rtems_message_queue_delete`` - Delete a queue + +- ``rtems_message_queue_send`` - Put message at rear of a queue + +- ``rtems_message_queue_urgent`` - Put message at front of a queue + +- ``rtems_message_queue_broadcast`` - Broadcast N messages to a queue + +- ``rtems_message_queue_receive`` - Receive message from a queue + +- ``rtems_message_queue_get_number_pending`` - Get number of messages pending on a queue + +- ``rtems_message_queue_flush`` - Flush all messages on a queue + +Background +========== + +Messages +-------- + +A message is a variable length buffer where +information can be stored to support communication. The length +of the message and the information stored in that message are +user-defined and can be actual data, pointer(s), or empty. + +Message Queues +-------------- + +A message queue permits the passing of messages among +tasks and ISRs. Message queues can contain a variable number of +messages. Normally messages are sent to and received from the +queue in FIFO order using the ``rtems_message_queue_send`` +directive. However, the ``rtems_message_queue_urgent`` +directive can be used to place +messages at the head of a queue in LIFO order. + +Synchronization can be accomplished when a task can +wait for a message to arrive at a queue. Also, a task may poll +a queue for the arrival of a message. + +The maximum length message which can be sent is set +on a per message queue basis. The message content must be copied in general +to/from an internal buffer of the message queue or directly to a peer in +certain cases. This copy operation is performed with interrupts disabled. So +it is advisable to keep the messages as short as possible. + +Building a Message Queue Attribute Set +-------------------------------------- +.. index:: message queue attributes + +In general, an attribute set is built by a bitwise OR +of the desired attribute components. The set of valid message +queue attributes is provided in the following table: + +- ``RTEMS_FIFO`` - tasks wait by FIFO (default) + +- ``RTEMS_PRIORITY`` - tasks wait by priority + +- ``RTEMS_LOCAL`` - local message queue (default) + +- ``RTEMS_GLOBAL`` - global message queue + +An attribute listed as a default is not required to +appear in the attribute list, although it is a good programming +practice to specify default attributes. If all defaults are +desired, the attribute ``RTEMS_DEFAULT_ATTRIBUTES`` +should be specified on this call. + +This example demonstrates the attribute_set parameter +needed to create a local message queue with the task priority +waiting queue discipline. The attribute_set parameter to the``rtems_message_queue_create`` directive could be either``RTEMS_PRIORITY`` or``RTEMS_LOCAL | RTEMS_PRIORITY``. +The attribute_set parameter can be set to ``RTEMS_PRIORITY`` +because ``RTEMS_LOCAL`` is the default for all created +message queues. If a similar message queue were to be known globally, then the +attribute_set parameter would be``RTEMS_GLOBAL | RTEMS_PRIORITY``. + +Building a MESSAGE_QUEUE_RECEIVE Option Set +------------------------------------------- + +In general, an option is built by a bitwise OR of the +desired option components. The set of valid options for the``rtems_message_queue_receive`` directive are +listed in the following table: + +- ``RTEMS_WAIT`` - task will wait for a message (default) + +- ``RTEMS_NO_WAIT`` - task should not wait + +An option listed as a default is not required to +appear in the option OR list, although it is a good programming +practice to specify default options. If all defaults are +desired, the option ``RTEMS_DEFAULT_OPTIONS`` should +be specified on this call. + +This example demonstrates the option parameter needed +to poll for a message to arrive. The option parameter passed to +the ``rtems_message_queue_receive`` directive should +be ``RTEMS_NO_WAIT``. + +Operations +========== + +Creating a Message Queue +------------------------ + +The ``rtems_message_queue_create`` directive creates a message +queue with the user-defined name. The user specifies the +maximum message size and maximum number of messages which can be +placed in the message queue at one time. The user may select +FIFO or task priority as the method for placing waiting tasks in +the task wait queue. RTEMS allocates a Queue Control Block +(QCB) from the QCB free list to maintain the newly created queue +as well as memory for the message buffer pool associated with +this message queue. RTEMS also generates a message queue ID +which is returned to the calling task. + +For GLOBAL message queues, the maximum message size +is effectively limited to the longest message which the MPCI is +capable of transmitting. + +Obtaining Message Queue IDs +--------------------------- + +When a message queue is created, RTEMS generates a +unique message queue ID. The message queue ID may be obtained +by either of two methods. First, as the result of an invocation +of the ``rtems_message_queue_create`` directive, the +queue ID is stored in a user provided location. Second, the queue +ID may be obtained later using the ``rtems_message_queue_ident`` +directive. The queue ID is used by other message manager +directives to access this message queue. + +Receiving a Message +------------------- + +The ``rtems_message_queue_receive`` directive attempts to +retrieve a message from the specified message queue. If at +least one message is in the queue, then the message is removed +from the queue, copied to the caller’s message buffer, and +returned immediately along with the length of the message. When +messages are unavailable, one of the following situations +applies: + +- By default, the calling task will wait forever for the + message to arrive. + +- Specifying the ``RTEMS_NO_WAIT`` option forces an immediate return + with an error status code. + +- Specifying a timeout limits the period the task will + wait before returning with an error status. + +If the task waits for a message, then it is placed in +the message queue’s task wait queue in either FIFO or task +priority order. All tasks waiting on a message queue are +returned an error code when the message queue is deleted. + +Sending a Message +----------------- + +Messages can be sent to a queue with the``rtems_message_queue_send`` and``rtems_message_queue_urgent`` directives. These +directives work identically when tasks are waiting to receive a +message. A task is removed from the task waiting queue, +unblocked, and the message is copied to a waiting task’s +message buffer. + +When no tasks are waiting at the queue,``rtems_message_queue_send`` places the +message at the rear of the message queue, while``rtems_message_queue_urgent`` places the message at the +front of the queue. The message is copied to a message buffer +from this message queue’s buffer pool and then placed in the +message queue. Neither directive can successfully send a +message to a message queue which has a full queue of pending +messages. + +Broadcasting a Message +---------------------- + +The ``rtems_message_queue_broadcast`` directive sends the same +message to every task waiting on the specified message queue as +an atomic operation. The message is copied to each waiting +task’s message buffer and each task is unblocked. The number of +tasks which were unblocked is returned to the caller. + +Deleting a Message Queue +------------------------ + +The ``rtems_message_queue_delete`` directive removes a message +queue from the system and frees its control block as well as the +memory associated with this message queue’s message buffer pool. +A message queue can be deleted by any local task that knows the +message queue’s ID. As a result of this directive, all tasks +blocked waiting to receive a message from the message queue will +be readied and returned a status code which indicates that the +message queue was deleted. Any subsequent references to the +message queue’s name and ID are invalid. Any messages waiting +at the message queue are also deleted and deallocated. + +Directives +========== + +This section details the message manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +MESSAGE_QUEUE_CREATE - Create a queue +------------------------------------- +.. index:: create a message queue + +**CALLING SEQUENCE:** + +.. index:: rtems_message_queue_create + +.. code:: c + + rtems_status_code rtems_message_queue_create( + rtems_name name, + uint32_t count, + size_t max_message_size, + rtems_attribute attribute_set, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - queue created successfully +``RTEMS_INVALID_NAME`` - invalid queue name +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NUMBER`` - invalid message count +``RTEMS_INVALID_SIZE`` - invalid message size +``RTEMS_TOO_MANY`` - too many queues created +``RTEMS_UNSATISFIED`` - unable to allocate message buffers +``RTEMS_MP_NOT_CONFIGURED`` - multiprocessing not configured +``RTEMS_TOO_MANY`` - too many global objects + +**DESCRIPTION:** + +This directive creates a message queue which resides +on the local node with the user-defined name specified in name. +For control and maintenance of the queue, RTEMS allocates and +initializes a QCB. Memory is allocated from the RTEMS Workspace +for the specified count of messages, each of max_message_size +bytes in length. The RTEMS-assigned queue id, returned in id, +is used to access the message queue. + +Specifying ``RTEMS_PRIORITY`` in attribute_set causes tasks +waiting for a message to be serviced according to task priority. +When ``RTEMS_FIFO`` is specified, waiting tasks are serviced +in First In-First Out order. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +The following message queue attribute constants are +defined by RTEMS: + +- ``RTEMS_FIFO`` - tasks wait by FIFO (default) + +- ``RTEMS_PRIORITY`` - tasks wait by priority + +- ``RTEMS_LOCAL`` - local message queue (default) + +- ``RTEMS_GLOBAL`` - global message queue + +Message queues should not be made global unless +remote tasks must interact with the created message queue. This +is to avoid the system overhead incurred by the creation of a +global message queue. When a global message queue is created, +the message queue’s name and id must be transmitted to every +node in the system for insertion in the local copy of the global +object table. + +For GLOBAL message queues, the maximum message size +is effectively limited to the longest message which the MPCI is +capable of transmitting. + +The total number of global objects, including message +queues, is limited by the maximum_global_objects field in the +configuration table. + +MESSAGE_QUEUE_IDENT - Get ID of a queue +--------------------------------------- +.. index:: get ID of a message queue + +**CALLING SEQUENCE:** + +.. index:: rtems_message_queue_ident + +.. code:: c + + rtems_status_code rtems_message_queue_ident( + rtems_name name, + uint32_t node, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - queue identified successfully +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - queue name not found +``RTEMS_INVALID_NODE`` - invalid node id + +**DESCRIPTION:** + +This directive obtains the queue id associated with +the queue name specified in name. If the queue name is not +unique, then the queue id will match one of the queues with that +name. However, this queue id is not guaranteed to correspond to +the desired queue. The queue id is used with other message +related directives to access the message queue. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +If node is ``RTEMS_SEARCH_ALL_NODES``, all nodes are searched +with the local node being searched first. All other nodes are +searched with the lowest numbered node searched first. + +If node is a valid node number which does not +represent the local node, then only the message queues exported +by the designated node are searched. + +This directive does not generate activity on remote +nodes. It accesses only the local copy of the global object +table. + +MESSAGE_QUEUE_DELETE - Delete a queue +------------------------------------- +.. index:: delete a message queue + +**CALLING SEQUENCE:** + +.. index:: rtems_message_queue_delete + +.. code:: c + + rtems_status_code rtems_message_queue_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - queue deleted successfully +``RTEMS_INVALID_ID`` - invalid queue id +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - cannot delete remote queue + +**DESCRIPTION:** + +This directive deletes the message queue specified by +id. As a result of this directive, all tasks blocked waiting to +receive a message from this queue will be readied and returned a +status code which indicates that the message queue was deleted. +If no tasks are waiting, but the queue contains messages, then +RTEMS returns these message buffers back to the system message +buffer pool. The QCB for this queue as well as the memory for +the message buffers is reclaimed by RTEMS. + +**NOTES:** + +The calling task will be preempted if its preemption +mode is enabled and one or more local tasks with a higher +priority than the calling task are waiting on the deleted queue. +The calling task will NOT be preempted if the tasks that are +waiting are remote tasks. + +The calling task does not have to be the task that +created the queue, although the task and queue must reside on +the same node. + +When the queue is deleted, any messages in the queue +are returned to the free message buffer pool. Any information +stored in those messages is lost. + +When a global message queue is deleted, the message +queue id must be transmitted to every node in the system for +deletion from the local copy of the global object table. + +Proxies, used to represent remote tasks, are +reclaimed when the message queue is deleted. + +MESSAGE_QUEUE_SEND - Put message at rear of a queue +--------------------------------------------------- +.. index:: send message to a queue + +**CALLING SEQUENCE:** + +.. index:: rtems_message_queue_send + +.. code:: c + + rtems_status_code rtems_message_queue_send( + rtems_id id, + cons void \*buffer, + size_t size + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - message sent successfully +``RTEMS_INVALID_ID`` - invalid queue id +``RTEMS_INVALID_SIZE`` - invalid message size +``RTEMS_INVALID_ADDRESS`` - ``buffer`` is NULL +``RTEMS_UNSATISFIED`` - out of message buffers +``RTEMS_TOO_MANY`` - queue’s limit has been reached + +**DESCRIPTION:** + +This directive sends the message buffer of size bytes +in length to the queue specified by id. If a task is waiting at +the queue, then the message is copied to the waiting task’s +buffer and the task is unblocked. If no tasks are waiting at the +queue, then the message is copied to a message buffer which is +obtained from this message queue’s message buffer pool. The +message buffer is then placed at the rear of the queue. + +**NOTES:** + +The calling task will be preempted if it has +preemption enabled and a higher priority task is unblocked as +the result of this directive. + +Sending a message to a global message queue which +does not reside on the local node will generate a request to the +remote node to post the message on the specified message queue. + +If the task to be unblocked resides on a different +node from the message queue, then the message is forwarded to +the appropriate node, the waiting task is unblocked, and the +proxy used to represent the task is reclaimed. + +MESSAGE_QUEUE_URGENT - Put message at front of a queue +------------------------------------------------------ +.. index:: put message at front of queue + +**CALLING SEQUENCE:** + +.. index:: rtems_message_queue_urgent + +.. code:: c + + rtems_status_code rtems_message_queue_urgent( + rtems_id id, + const void \*buffer, + size_t size + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - message sent successfully +``RTEMS_INVALID_ID`` - invalid queue id +``RTEMS_INVALID_SIZE`` - invalid message size +``RTEMS_INVALID_ADDRESS`` - ``buffer`` is NULL +``RTEMS_UNSATISFIED`` - out of message buffers +``RTEMS_TOO_MANY`` - queue’s limit has been reached + +**DESCRIPTION:** + +This directive sends the message buffer of size bytes +in length to the queue specified by id. If a task is waiting on +the queue, then the message is copied to the task’s buffer and +the task is unblocked. If no tasks are waiting on the queue, +then the message is copied to a message buffer which is obtained +from this message queue’s message buffer pool. The message +buffer is then placed at the front of the queue. + +**NOTES:** + +The calling task will be preempted if it has +preemption enabled and a higher priority task is unblocked as +the result of this directive. + +Sending a message to a global message queue which +does not reside on the local node will generate a request +telling the remote node to post the message on the specified +message queue. + +If the task to be unblocked resides on a different +node from the message queue, then the message is forwarded to +the appropriate node, the waiting task is unblocked, and the +proxy used to represent the task is reclaimed. + +MESSAGE_QUEUE_BROADCAST - Broadcast N messages to a queue +--------------------------------------------------------- +.. index:: broadcast message to a queue + +**CALLING SEQUENCE:** + +.. index:: rtems_message_queue_broadcast + +.. code:: c + + rtems_status_code rtems_message_queue_broadcast( + rtems_id id, + const void \*buffer, + size_t size, + uint32_t \*count + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - message broadcasted successfully +``RTEMS_INVALID_ID`` - invalid queue id +``RTEMS_INVALID_ADDRESS`` - ``buffer`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``count`` is NULL +``RTEMS_INVALID_SIZE`` - invalid message size + +**DESCRIPTION:** + +This directive causes all tasks that are waiting at +the queue specified by id to be unblocked and sent the message +contained in buffer. Before a task is unblocked, the message +buffer of size byes in length is copied to that task’s message +buffer. The number of tasks that were unblocked is returned in +count. + +**NOTES:** + +The calling task will be preempted if it has +preemption enabled and a higher priority task is unblocked as +the result of this directive. + +The execution time of this directive is directly +related to the number of tasks waiting on the message queue, +although it is more efficient than the equivalent number of +invocations of ``rtems_message_queue_send``. + +Broadcasting a message to a global message queue +which does not reside on the local node will generate a request +telling the remote node to broadcast the message to the +specified message queue. + +When a task is unblocked which resides on a different +node from the message queue, a copy of the message is forwarded +to the appropriate node, the waiting task is unblocked, and the +proxy used to represent the task is reclaimed. + +MESSAGE_QUEUE_RECEIVE - Receive message from a queue +---------------------------------------------------- +.. index:: receive message from a queue + +**CALLING SEQUENCE:** + +.. index:: rtems_message_queue_receive + +.. code:: c + + rtems_status_code rtems_message_queue_receive( + rtems_id id, + void \*buffer, + size_t \*size, + rtems_option option_set, + rtems_interval timeout + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - message received successfully +``RTEMS_INVALID_ID`` - invalid queue id +``RTEMS_INVALID_ADDRESS`` - ``buffer`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``size`` is NULL +``RTEMS_UNSATISFIED`` - queue is empty +``RTEMS_TIMEOUT`` - timed out waiting for message +``RTEMS_OBJECT_WAS_DELETED`` - queue deleted while waiting + +**DESCRIPTION:** + +This directive receives a message from the message +queue specified in id. The ``RTEMS_WAIT`` and ``RTEMS_NO_WAIT`` options of the +options parameter allow the calling task to specify whether to +wait for a message to become available or return immediately. +For either option, if there is at least one message in the +queue, then it is copied to buffer, size is set to return the +length of the message in bytes, and this directive returns +immediately with a successful return code. The buffer has to be big enough to +receive a message of the maximum length with respect to this message queue. + +If the calling task chooses to return immediately and +the queue is empty, then a status code indicating this condition +is returned. If the calling task chooses to wait at the message +queue and the queue is empty, then the calling task is placed on +the message wait queue and blocked. If the queue was created +with the ``RTEMS_PRIORITY`` option specified, then +the calling task is inserted into the wait queue according to +its priority. But, if the queue was created with the``RTEMS_FIFO`` option specified, then the +calling task is placed at the rear of the wait queue. + +A task choosing to wait at the queue can optionally +specify a timeout value in the timeout parameter. The timeout +parameter specifies the maximum interval to wait before the +calling task desires to be unblocked. If it is set to``RTEMS_NO_TIMEOUT``, then the calling task will wait forever. + +**NOTES:** + +The following message receive option constants are +defined by RTEMS: + +- ``RTEMS_WAIT`` - task will wait for a message (default) + +- ``RTEMS_NO_WAIT`` - task should not wait + +Receiving a message from a global message queue which +does not reside on the local node will generate a request to the +remote node to obtain a message from the specified message +queue. If no message is available and ``RTEMS_WAIT`` was specified, then +the task must be blocked until a message is posted. A proxy is +allocated on the remote node to represent the task until the +message is posted. + +A clock tick is required to support the timeout functionality of +this directive. + +MESSAGE_QUEUE_GET_NUMBER_PENDING - Get number of messages pending on a queue +---------------------------------------------------------------------------- +.. index:: get number of pending messages + +**CALLING SEQUENCE:** + +.. index:: rtems_message_queue_get_number_pending + +.. code:: c + + rtems_status_code rtems_message_queue_get_number_pending( + rtems_id id, + uint32_t \*count + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - number of messages pending returned successfully +``RTEMS_INVALID_ADDRESS`` - ``count`` is NULL +``RTEMS_INVALID_ID`` - invalid queue id + +**DESCRIPTION:** + +This directive returns the number of messages pending on this +message queue in count. If no messages are present +on the queue, count is set to zero. + +**NOTES:** + +Getting the number of pending messages on a global message queue which +does not reside on the local node will generate a request to the +remote node to actually obtain the pending message count for +the specified message queue. + +MESSAGE_QUEUE_FLUSH - Flush all messages on a queue +--------------------------------------------------- +.. index:: flush messages on a queue + +**CALLING SEQUENCE:** + +.. index:: rtems_message_queue_flush + +.. code:: c + + rtems_status_code rtems_message_queue_flush( + rtems_id id, + uint32_t \*count + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - message queue flushed successfully +``RTEMS_INVALID_ADDRESS`` - ``count`` is NULL +``RTEMS_INVALID_ID`` - invalid queue id + +**DESCRIPTION:** + +This directive removes all pending messages from the +specified queue id. The number of messages removed is returned +in count. If no messages are present on the queue, count is set +to zero. + +**NOTES:** + +Flushing all messages on a global message queue which +does not reside on the local node will generate a request to the +remote node to actually flush the specified message queue. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Event Manager +############# + +.. index:: events + +Introduction +============ + +The event manager provides a high performance method +of intertask communication and synchronization. The directives +provided by the event manager are: + +- ``rtems_event_send`` - Send event set to a task + +- ``rtems_event_receive`` - Receive event condition + +Background +========== + +Event Sets +---------- +.. index:: event flag, definition +.. index:: event set, definition +.. index:: rtems_event_set + +An event flag is used by a task (or ISR) to inform +another task of the occurrence of a significant situation. +Thirty-two event flags are associated with each task. A +collection of one or more event flags is referred to as an event +set. The data type ``rtems_event_set`` is used to manage +event sets. + +The application developer should remember the following +key characteristics of event operations when utilizing the event +manager: + +- Events provide a simple synchronization facility. + +- Events are aimed at tasks. + +- Tasks can wait on more than one event simultaneously. + +- Events are independent of one another. + +- Events do not hold or transport data. + +- Events are not queued. In other words, if an event is + sent more than once to a task before being received, the second and + subsequent send operations to that same task have no effect. + +An event set is posted when it is directed (or sent) to a task. A +pending event is an event that has been posted but not received. An event +condition is used to specify the event set which the task desires to receive +and the algorithm which will be used to determine when the request is +satisfied. An event condition is satisfied based upon one of two +algorithms which are selected by the user. The``RTEMS_EVENT_ANY`` algorithm states that an event condition +is satisfied when at least a single requested event is posted. The``RTEMS_EVENT_ALL`` algorithm states that an event condition +is satisfied when every requested event is posted. + +Building an Event Set or Condition +---------------------------------- +.. index:: event condition, building +.. index:: event set, building + +An event set or condition is built by a bitwise OR of +the desired events. The set of valid events is ``RTEMS_EVENT_0`` through``RTEMS_EVENT_31``. If an event is not explicitly specified in the set or +condition, then it is not present. Events are specifically +designed to be mutually exclusive, therefore bitwise OR and +addition operations are equivalent as long as each event appears +exactly once in the event set list. + +For example, when sending the event set consisting of``RTEMS_EVENT_6``, ``RTEMS_EVENT_15``, and ``RTEMS_EVENT_31``, +the event parameter to the ``rtems_event_send`` +directive should be ``RTEMS_EVENT_6 | +RTEMS_EVENT_15 | RTEMS_EVENT_31``. + +Building an EVENT_RECEIVE Option Set +------------------------------------ + +In general, an option is built by a bitwise OR of the +desired option components. The set of valid options for the``rtems_event_receive`` directive are listed +in the following table: + +- ``RTEMS_WAIT`` - task will wait for event (default) + +- ``RTEMS_NO_WAIT`` - task should not wait + +- ``RTEMS_EVENT_ALL`` - return after all events (default) + +- ``RTEMS_EVENT_ANY`` - return after any events + +Option values are specifically designed to be +mutually exclusive, therefore bitwise OR and addition operations +are equivalent as long as each option appears exactly once in +the component list. An option listed as a default is not +required to appear in the option list, although it is a good +programming practice to specify default options. If all +defaults are desired, the option ``RTEMS_DEFAULT_OPTIONS`` should be +specified on this call. + +This example demonstrates the option parameter needed +to poll for all events in a particular event condition to +arrive. The option parameter passed to the``rtems_event_receive`` directive should be either``RTEMS_EVENT_ALL | RTEMS_NO_WAIT`` +or ``RTEMS_NO_WAIT``. The option parameter can be set to``RTEMS_NO_WAIT`` because ``RTEMS_EVENT_ALL`` is the +default condition for ``rtems_event_receive``. + +Operations +========== + +Sending an Event Set +-------------------- + +The ``rtems_event_send`` directive allows a task (or an ISR) to +direct an event set to a target task. Based upon the state of +the target task, one of the following situations applies: + +- Target Task is Blocked Waiting for Events + + - If the waiting task’s input event condition is + satisfied, then the task is made ready for execution. + + - If the waiting task’s input event condition is not + satisfied, then the event set is posted but left pending and the + task remains blocked. + +- Target Task is Not Waiting for Events + + - The event set is posted and left pending. + +Receiving an Event Set +---------------------- + +The ``rtems_event_receive`` directive is used by tasks to +accept a specific input event condition. The task also +specifies whether the request is satisfied when all requested +events are available or any single requested event is available. +If the requested event condition is satisfied by pending +events, then a successful return code and the satisfying event +set are returned immediately. If the condition is not +satisfied, then one of the following situations applies: + +- By default, the calling task will wait forever for the + event condition to be satisfied. + +- Specifying the ``RTEMS_NO_WAIT`` option forces an immediate return + with an error status code. + +- Specifying a timeout limits the period the task will + wait before returning with an error status code. + +Determining the Pending Event Set +--------------------------------- + +A task can determine the pending event set by calling +the ``rtems_event_receive`` directive with a value of``RTEMS_PENDING_EVENTS`` for the input event condition. +The pending events are returned to the calling task but the event +set is left unaltered. + +Receiving all Pending Events +---------------------------- + +A task can receive all of the currently pending +events by calling the ``rtems_event_receive`` +directive with a value of ``RTEMS_ALL_EVENTS`` +for the input event condition and``RTEMS_NO_WAIT | RTEMS_EVENT_ANY`` +for the option set. The pending events are returned to the +calling task and the event set is cleared. If no events are +pending then the ``RTEMS_UNSATISFIED`` status code will be returned. + +Directives +========== + +This section details the event manager’s directives. +A subsection is dedicated to each of this manager’s directives +and describes the calling sequence, related constants, usage, +and status codes. + +EVENT_SEND - Send event set to a task +------------------------------------- +.. index:: send event set to a task + +**CALLING SEQUENCE:** + +.. index:: rtems_event_send + +.. code:: c + + rtems_status_code rtems_event_send ( + rtems_id id, + rtems_event_set event_in + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - event set sent successfully +``RTEMS_INVALID_ID`` - invalid task id + +**DESCRIPTION:** + +This directive sends an event set, event_in, to the +task specified by id. If a blocked task’s input event condition +is satisfied by this directive, then it will be made ready. If +its input event condition is not satisfied, then the events +satisfied are updated and the events not satisfied are left +pending. If the task specified by id is not blocked waiting for +events, then the events sent are left pending. + +**NOTES:** + +Specifying ``RTEMS_SELF`` for id results in the event set being +sent to the calling task. + +Identical events sent to a task are not queued. In +other words, the second, and subsequent, posting of an event to +a task before it can perform an ``rtems_event_receive`` +has no effect. + +The calling task will be preempted if it has +preemption enabled and a higher priority task is unblocked as +the result of this directive. + +Sending an event set to a global task which does not +reside on the local node will generate a request telling the +remote node to send the event set to the appropriate task. + +EVENT_RECEIVE - Receive event condition +--------------------------------------- +.. index:: receive event condition + +**CALLING SEQUENCE:** + +.. index:: rtems_event_receive + +.. code:: c + + rtems_status_code rtems_event_receive ( + rtems_event_set event_in, + rtems_option option_set, + rtems_interval ticks, + rtems_event_set \*event_out + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - event received successfully +``RTEMS_UNSATISFIED`` - input event not satisfied (``RTEMS_NO_WAIT``) +``RTEMS_INVALID_ADDRESS`` - ``event_out`` is NULL +``RTEMS_TIMEOUT`` - timed out waiting for event + +**DESCRIPTION:** + +This directive attempts to receive the event +condition specified in event_in. If event_in is set to``RTEMS_PENDING_EVENTS``, then the current pending events are returned in +event_out and left pending. The ``RTEMS_WAIT`` and ``RTEMS_NO_WAIT`` options in the +option_set parameter are used to specify whether or not the task +is willing to wait for the event condition to be satisfied.``RTEMS_EVENT_ANY`` and ``RTEMS_EVENT_ALL`` are used in the option_set parameter are +used to specify whether a single event or the complete event set +is necessary to satisfy the event condition. The event_out +parameter is returned to the calling task with the value that +corresponds to the events in event_in that were satisfied. + +If pending events satisfy the event condition, then +event_out is set to the satisfied events and the pending events +in the event condition are cleared. If the event condition is +not satisfied and ``RTEMS_NO_WAIT`` is specified, then event_out is set to +the currently satisfied events. If the calling task chooses to +wait, then it will block waiting for the event condition. + +If the calling task must wait for the event condition +to be satisfied, then the timeout parameter is used to specify +the maximum interval to wait. If it is set to ``RTEMS_NO_TIMEOUT``, then +the calling task will wait forever. + +**NOTES:** + +This directive only affects the events specified in +event_in. Any pending events that do not correspond to any of +the events specified in event_in will be left pending. + +The following event receive option constants are defined by +RTEMS: + +- ``RTEMS_WAIT`` task will wait for event (default) + +- ``RTEMS_NO_WAIT`` task should not wait + +- ``RTEMS_EVENT_ALL`` return after all events (default) + +- ``RTEMS_EVENT_ANY`` return after any events + +A clock tick is required to support the functionality of this directive. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Signal Manager +############## + +.. index:: signals + +Introduction +============ + +The signal manager provides the capabilities required +for asynchronous communication. The directives provided by the +signal manager are: + +- ``rtems_signal_catch`` - Establish an ASR + +- ``rtems_signal_send`` - Send signal set to a task + +Background +========== + +Signal Manager Definitions +-------------------------- +.. index:: asynchronous signal routine +.. index:: ASR + +The signal manager allows a task to optionally define +an asynchronous signal routine (ASR). An ASR is to a task what +an ISR is to an application’s set of tasks. When the processor +is interrupted, the execution of an application is also +interrupted and an ISR is given control. Similarly, when a +signal is sent to a task, that task’s execution path will be +"interrupted" by the ASR. Sending a signal to a task has no +effect on the receiving task’s current execution state... index:: rtems_signal_set + +A signal flag is used by a task (or ISR) to inform +another task of the occurrence of a significant situation. +Thirty-two signal flags are associated with each task. A +collection of one or more signals is referred to as a signal +set. The data type ``rtems_signal_set`` +is used to manipulate signal sets. + +A signal set is posted when it is directed (or sent) to a +task. A pending signal is a signal that has been sent to a task +with a valid ASR, but has not been processed by that task’s ASR. + +A Comparison of ASRs and ISRs +----------------------------- +.. index:: ASR vs. ISR +.. index:: ISR vs. ASR + +The format of an ASR is similar to that of an ISR +with the following exceptions: + +- ISRs are scheduled by the processor hardware. ASRs are + scheduled by RTEMS. + +- ISRs do not execute in the context of a task and may + invoke only a subset of directives. ASRs execute in the context + of a task and may execute any directive. + +- When an ISR is invoked, it is passed the vector number + as its argument. When an ASR is invoked, it is passed the + signal set as its argument. + +- An ASR has a task mode which can be different from that + of the task. An ISR does not execute as a task and, as a + result, does not have a task mode. + +Building a Signal Set +--------------------- +.. index:: signal set, building + +A signal set is built by a bitwise OR of the desired +signals. The set of valid signals is ``RTEMS_SIGNAL_0`` through``RTEMS_SIGNAL_31``. If a signal is not explicitly specified in the +signal set, then it is not present. Signal values are +specifically designed to be mutually exclusive, therefore +bitwise OR and addition operations are equivalent as long as +each signal appears exactly once in the component list. + +This example demonstrates the signal parameter used +when sending the signal set consisting of``RTEMS_SIGNAL_6``,``RTEMS_SIGNAL_15``, and``RTEMS_SIGNAL_31``. The signal parameter provided +to the ``rtems_signal_send`` directive should be``RTEMS_SIGNAL_6 | +RTEMS_SIGNAL_15 | RTEMS_SIGNAL_31``. + +Building an ASR Mode +-------------------- +.. index:: ASR mode, building + +In general, an ASR’s mode is built by a bitwise OR of +the desired mode components. The set of valid mode components +is the same as those allowed with the task_create and task_mode +directives. A complete list of mode options is provided in the +following table: + +- ``RTEMS_PREEMPT`` is masked by``RTEMS_PREEMPT_MASK`` and enables preemption + +- ``RTEMS_NO_PREEMPT`` is masked by``RTEMS_PREEMPT_MASK`` and disables preemption + +- ``RTEMS_NO_TIMESLICE`` is masked by``RTEMS_TIMESLICE_MASK`` and disables timeslicing + +- ``RTEMS_TIMESLICE`` is masked by``RTEMS_TIMESLICE_MASK`` and enables timeslicing + +- ``RTEMS_ASR`` is masked by``RTEMS_ASR_MASK`` and enables ASR processing + +- ``RTEMS_NO_ASR`` is masked by``RTEMS_ASR_MASK`` and disables ASR processing + +- ``RTEMS_INTERRUPT_LEVEL(0)`` is masked by``RTEMS_INTERRUPT_MASK`` and enables all interrupts + +- ``RTEMS_INTERRUPT_LEVEL(n)`` is masked by``RTEMS_INTERRUPT_MASK`` and sets interrupts level n + +Mode values are specifically designed to be mutually +exclusive, therefore bitwise OR and addition operations are +equivalent as long as each mode appears exactly once in the +component list. A mode component listed as a default is not +required to appear in the mode list, although it is a good +programming practice to specify default components. If all +defaults are desired, the mode DEFAULT_MODES should be specified +on this call. + +This example demonstrates the mode parameter used +with the ``rtems_signal_catch`` +to establish an ASR which executes at +interrupt level three and is non-preemptible. The mode should +be set to``RTEMS_INTERRUPT_LEVEL(3) | RTEMS_NO_PREEMPT`` +to indicate the +desired processor mode and interrupt level. + +Operations +========== + +Establishing an ASR +------------------- + +The ``rtems_signal_catch`` directive establishes an ASR for the +calling task. The address of the ASR and its execution mode are +specified to this directive. The ASR’s mode is distinct from +the task’s mode. For example, the task may allow preemption, +while that task’s ASR may have preemption disabled. Until a +task calls ``rtems_signal_catch`` the first time, +its ASR is invalid, and no signal sets can be sent to the task. + +A task may invalidate its ASR and discard all pending +signals by calling ``rtems_signal_catch`` +with a value of NULL for the ASR’s address. When a task’s +ASR is invalid, new signal sets sent to this task are discarded. + +A task may disable ASR processing (``RTEMS_NO_ASR``) via the +task_mode directive. When a task’s ASR is disabled, the signals +sent to it are left pending to be processed later when the ASR +is enabled. + +Any directive that can be called from a task can also +be called from an ASR. A task is only allowed one active ASR. +Thus, each call to ``rtems_signal_catch`` +replaces the previous one. + +Normally, signal processing is disabled for the ASR’s +execution mode, but if signal processing is enabled for the ASR, +the ASR must be reentrant. + +Sending a Signal Set +-------------------- + +The ``rtems_signal_send`` directive allows both +tasks and ISRs to send signals to a target task. The target task and +a set of signals are specified to the``rtems_signal_send`` directive. The sending +of a signal to a task has no effect on the execution state of +that task. If the task is not the currently running task, then +the signals are left pending and processed by the task’s ASR the +next time the task is dispatched to run. The ASR is executed +immediately before the task is dispatched. If the currently +running task sends a signal to itself or is sent a signal from +an ISR, its ASR is immediately dispatched to run provided signal +processing is enabled. + +If an ASR with signals enabled is preempted by +another task or an ISR and a new signal set is sent, then a new +copy of the ASR will be invoked, nesting the preempted ASR. +Upon completion of processing the new signal set, control will +return to the preempted ASR. In this situation, the ASR must be +reentrant. + +Like events, identical signals sent to a task are not +queued. In other words, sending the same signal multiple times +to a task (without any intermediate signal processing occurring +for the task), has the same result as sending that signal to +that task once. + +Processing an ASR +----------------- + +Asynchronous signals were designed to provide the +capability to generate software interrupts. The processing of +software interrupts parallels that of hardware interrupts. As a +result, the differences between the formats of ASRs and ISRs is +limited to the meaning of the single argument passed to an ASR. +The ASR should have the following calling sequence and adhere to +C calling conventions:.. index:: rtems_asr + +.. code:: c + + rtems_asr user_routine( + rtems_signal_set signals + ); + +When the ASR returns to RTEMS the mode and execution +path of the interrupted task (or ASR) is restored to the context +prior to entering the ASR. + +Directives +========== + +This section details the signal manager’s directives. +A subsection is dedicated to each of this manager’s directives +and describes the calling sequence, related constants, usage, +and status codes. + +SIGNAL_CATCH - Establish an ASR +------------------------------- +.. index:: establish an ASR +.. index:: install an ASR + +**CALLING SEQUENCE:** + +.. index:: rtems_signal_catch + +.. code:: c + + rtems_status_code rtems_signal_catch( + rtems_asr_entry asr_handler, + rtems_mode mode + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - always successful + +**DESCRIPTION:** + +This directive establishes an asynchronous signal +routine (ASR) for the calling task. The asr_handler parameter +specifies the entry point of the ASR. If asr_handler is NULL, +the ASR for the calling task is invalidated and all pending +signals are cleared. Any signals sent to a task with an invalid +ASR are discarded. The mode parameter specifies the execution +mode for the ASR. This execution mode supersedes the task’s +execution mode while the ASR is executing. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +The following task mode constants are defined by RTEMS: + +- ``RTEMS_PREEMPT`` is masked by``RTEMS_PREEMPT_MASK`` and enables preemption + +- ``RTEMS_NO_PREEMPT`` is masked by``RTEMS_PREEMPT_MASK`` and disables preemption + +- ``RTEMS_NO_TIMESLICE`` is masked by``RTEMS_TIMESLICE_MASK`` and disables timeslicing + +- ``RTEMS_TIMESLICE`` is masked by``RTEMS_TIMESLICE_MASK`` and enables timeslicing + +- ``RTEMS_ASR`` is masked by``RTEMS_ASR_MASK`` and enables ASR processing + +- ``RTEMS_NO_ASR`` is masked by``RTEMS_ASR_MASK`` and disables ASR processing + +- ``RTEMS_INTERRUPT_LEVEL(0)`` is masked by``RTEMS_INTERRUPT_MASK`` and enables all interrupts + +- ``RTEMS_INTERRUPT_LEVEL(n)`` is masked by``RTEMS_INTERRUPT_MASK`` and sets interrupts level n + +SIGNAL_SEND - Send signal set to a task +--------------------------------------- +.. index:: send signal set + +**CALLING SEQUENCE:** + +.. index:: rtems_signal_send + +.. code:: c + + rtems_status_code rtems_signal_send( + rtems_id id, + rtems_signal_set signal_set + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - signal sent successfully +``RTEMS_INVALID_ID`` - task id invalid +``RTEMS_INVALID_NUMBER`` - empty signal set +``RTEMS_NOT_DEFINED`` - ASR invalid + +**DESCRIPTION:** + +This directive sends a signal set to the task +specified in id. The signal_set parameter contains the signal +set to be sent to the task. + +If a caller sends a signal set to a task with an +invalid ASR, then an error code is returned to the caller. If a +caller sends a signal set to a task whose ASR is valid but +disabled, then the signal set will be caught and left pending +for the ASR to process when it is enabled. If a caller sends a +signal set to a task with an ASR that is both valid and enabled, +then the signal set is caught and the ASR will execute the next +time the task is dispatched to run. + +**NOTES:** + +Sending a signal set to a task has no effect on that +task’s state. If a signal set is sent to a blocked task, then +the task will remain blocked and the signals will be processed +when the task becomes the running task. + +Sending a signal set to a global task which does not +reside on the local node will generate a request telling the +remote node to send the signal set to the specified task. + +.. COMMENT: COPYRIGHT (c) 1988-2010. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Partition Manager +################# + +.. index:: partitions + +Introduction +============ + +The partition manager provides facilities to +dynamically allocate memory in fixed-size units. The directives +provided by the partition manager are: + +- ``rtems_partition_create`` - Create a partition + +- ``rtems_partition_ident`` - Get ID of a partition + +- ``rtems_partition_delete`` - Delete a partition + +- ``rtems_partition_get_buffer`` - Get buffer from a partition + +- ``rtems_partition_return_buffer`` - Return buffer to a partition + +Background +========== + +Partition Manager Definitions +----------------------------- +.. index:: partition, definition + +A partition is a physically contiguous memory area +divided into fixed-size buffers that can be dynamically +allocated and deallocated... index:: buffers, definition + +Partitions are managed and maintained as a list of +buffers. Buffers are obtained from the front of the partition’s +free buffer chain and returned to the rear of the same chain. +When a buffer is on the free buffer chain, RTEMS uses two +pointers of memory from each buffer as the free buffer chain. +When a buffer is allocated, the entire buffer is available for application use. +Therefore, modifying memory that is outside of an allocated +buffer could destroy the free buffer chain or the contents of an +adjacent allocated buffer. + +Building a Partition Attribute Set +---------------------------------- +.. index:: partition attribute set, building + +In general, an attribute set is built by a bitwise OR +of the desired attribute components. The set of valid partition +attributes is provided in the following table: + +- ``RTEMS_LOCAL`` - local partition (default) + +- ``RTEMS_GLOBAL`` - global partition + +Attribute values are specifically designed to be +mutually exclusive, therefore bitwise OR and addition operations +are equivalent as long as each attribute appears exactly once in +the component list. An attribute listed as a default is not +required to appear in the attribute list, although it is a good +programming practice to specify default attributes. If all +defaults are desired, the attribute``RTEMS_DEFAULT_ATTRIBUTES`` should be +specified on this call. The attribute_set parameter should be``RTEMS_GLOBAL`` to indicate that the partition +is to be known globally. + +Operations +========== + +Creating a Partition +-------------------- + +The ``rtems_partition_create`` directive creates a partition +with a user-specified name. The partition’s name, starting +address, length and buffer size are all specified to the``rtems_partition_create`` directive. +RTEMS allocates a Partition Control +Block (PTCB) from the PTCB free list. This data structure is +used by RTEMS to manage the newly created partition. The number +of buffers in the partition is calculated based upon the +specified partition length and buffer size. If successful,the +unique partition ID is returned to the calling task. + +Obtaining Partition IDs +----------------------- + +When a partition is created, RTEMS generates a unique +partition ID and assigned it to the created partition until it +is deleted. The partition ID may be obtained by either of two +methods. First, as the result of an invocation of the``rtems_partition_create`` directive, the partition +ID is stored in a user provided location. Second, the partition +ID may be obtained later using the ``rtems_partition_ident`` +directive. The partition ID is used by other partition manager directives +to access this partition. + +Acquiring a Buffer +------------------ + +A buffer can be obtained by calling the``rtems_partition_get_buffer`` directive. +If a buffer is available, then +it is returned immediately with a successful return code. +Otherwise, an unsuccessful return code is returned immediately +to the caller. Tasks cannot block to wait for a buffer to +become available. + +Releasing a Buffer +------------------ + +Buffers are returned to a partition’s free buffer +chain with the ``rtems_partition_return_buffer`` directive. This +directive returns an error status code if the returned buffer +was not previously allocated from this partition. + +Deleting a Partition +-------------------- + +The ``rtems_partition_delete`` directive allows a partition to +be removed and returned to RTEMS. When a partition is deleted, +the PTCB for that partition is returned to the PTCB free list. +A partition with buffers still allocated cannot be deleted. Any +task attempting to do so will be returned an error status code. + +Directives +========== + +This section details the partition manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +PARTITION_CREATE - Create a partition +------------------------------------- +.. index:: create a partition + +**CALLING SEQUENCE:** + +.. index:: rtems_partition_create + +.. code:: c + + rtems_status_code rtems_partition_create( + rtems_name name, + void \*starting_address, + uint32_t length, + uint32_t buffer_size, + rtems_attribute attribute_set, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - partition created successfully +``RTEMS_INVALID_NAME`` - invalid partition name +``RTEMS_TOO_MANY`` - too many partitions created +``RTEMS_INVALID_ADDRESS`` - address not on four byte boundary +``RTEMS_INVALID_ADDRESS`` - ``starting_address`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_SIZE`` - length or buffer size is 0 +``RTEMS_INVALID_SIZE`` - length is less than the buffer size +``RTEMS_INVALID_SIZE`` - buffer size not a multiple of 4 +``RTEMS_MP_NOT_CONFIGURED`` - multiprocessing not configured +``RTEMS_TOO_MANY`` - too many global objects + +**DESCRIPTION:** + +This directive creates a partition of fixed size +buffers from a physically contiguous memory space which starts +at starting_address and is length bytes in size. Each allocated +buffer is to be of ``buffer_size`` in bytes. The assigned +partition id is returned in ``id``. This partition id is used to +access the partition with other partition related directives. +For control and maintenance of the partition, RTEMS allocates a +PTCB from the local PTCB free pool and initializes it. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +The ``starting_address`` must be properly aligned for the +target architecture. + +The ``buffer_size`` parameter must be a multiple of +the CPU alignment factor. Additionally, ``buffer_size`` +must be large enough to hold two pointers on the target +architecture. This is required for RTEMS to manage the +buffers when they are free. + +Memory from the partition is not used by RTEMS to +store the Partition Control Block. + +The following partition attribute constants are +defined by RTEMS: + +- ``RTEMS_LOCAL`` - local partition (default) + +- ``RTEMS_GLOBAL`` - global partition + +The PTCB for a global partition is allocated on the +local node. The memory space used for the partition must reside +in shared memory. Partitions should not be made global unless +remote tasks must interact with the partition. This is to avoid +the overhead incurred by the creation of a global partition. +When a global partition is created, the partition’s name and id +must be transmitted to every node in the system for insertion in +the local copy of the global object table. + +The total number of global objects, including +partitions, is limited by the maximum_global_objects field in +the Configuration Table. + +PARTITION_IDENT - Get ID of a partition +--------------------------------------- +.. index:: get ID of a partition +.. index:: obtain ID of a partition + +**CALLING SEQUENCE:** + +.. index:: rtems_partition_ident + +.. code:: c + + rtems_status_code rtems_partition_ident( + rtems_name name, + uint32_t node, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - partition identified successfully +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - partition name not found +``RTEMS_INVALID_NODE`` - invalid node id + +**DESCRIPTION:** + +This directive obtains the partition id associated +with the partition name. If the partition name is not unique, +then the partition id will match one of the partitions with that +name. However, this partition id is not guaranteed to +correspond to the desired partition. The partition id is used +with other partition related directives to access the partition. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +If node is ``RTEMS_SEARCH_ALL_NODES``, all nodes are searched +with the local node being searched first. All other nodes are +searched with the lowest numbered node searched first. + +If node is a valid node number which does not +represent the local node, then only the partitions exported by +the designated node are searched. + +This directive does not generate activity on remote +nodes. It accesses only the local copy of the global object +table. + +PARTITION_DELETE - Delete a partition +------------------------------------- +.. index:: delete a partition + +**CALLING SEQUENCE:** + +.. index:: rtems_partition_delete + +.. code:: c + + rtems_status_code rtems_partition_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - partition deleted successfully +``RTEMS_INVALID_ID`` - invalid partition id +``RTEMS_RESOURCE_IN_USE`` - buffers still in use +``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - cannot delete remote partition + +**DESCRIPTION:** + +This directive deletes the partition specified by id. +The partition cannot be deleted if any of its buffers are still +allocated. The PTCB for the deleted partition is reclaimed by +RTEMS. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +The calling task does not have to be the task that +created the partition. Any local task that knows the partition +id can delete the partition. + +When a global partition is deleted, the partition id +must be transmitted to every node in the system for deletion +from the local copy of the global object table. + +The partition must reside on the local node, even if +the partition was created with the ``RTEMS_GLOBAL`` option. + +PARTITION_GET_BUFFER - Get buffer from a partition +-------------------------------------------------- +.. index:: get buffer from partition +.. index:: obtain buffer from partition + +**CALLING SEQUENCE:** + +.. index:: rtems_partition_get_buffer + +.. code:: c + + rtems_status_code rtems_partition_get_buffer( + rtems_id id, + void \**buffer + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - buffer obtained successfully +``RTEMS_INVALID_ADDRESS`` - ``buffer`` is NULL +``RTEMS_INVALID_ID`` - invalid partition id +``RTEMS_UNSATISFIED`` - all buffers are allocated + +**DESCRIPTION:** + +This directive allows a buffer to be obtained from +the partition specified in id. The address of the allocated +buffer is returned in buffer. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +All buffers begin on a four byte boundary. + +A task cannot wait on a buffer to become available. + +Getting a buffer from a global partition which does +not reside on the local node will generate a request telling the +remote node to allocate a buffer from the specified partition. + +PARTITION_RETURN_BUFFER - Return buffer to a partition +------------------------------------------------------ +.. index:: return buffer to partitition + +**CALLING SEQUENCE:** + +.. index:: rtems_partition_return_buffer + +.. code:: c + + rtems_status_code rtems_partition_return_buffer( + rtems_id id, + void \*buffer + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - buffer returned successfully +``RTEMS_INVALID_ADDRESS`` - ``buffer`` is NULL +``RTEMS_INVALID_ID`` - invalid partition id +``RTEMS_INVALID_ADDRESS`` - buffer address not in partition + +**DESCRIPTION:** + +This directive returns the buffer specified by buffer +to the partition specified by id. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +Returning a buffer to a global partition which does +not reside on the local node will generate a request telling the +remote node to return the buffer to the specified partition. + +Returning a buffer multiple times is an error. It will corrupt the internal +state of the partition. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Region Manager +############## + +.. index:: regions + +Introduction +============ + +The region manager provides facilities to dynamically +allocate memory in variable sized units. The directives +provided by the region manager are: + +- ``rtems_region_create`` - Create a region + +- ``rtems_region_ident`` - Get ID of a region + +- ``rtems_region_delete`` - Delete a region + +- ``rtems_region_extend`` - Add memory to a region + +- ``rtems_region_get_segment`` - Get segment from a region + +- ``rtems_region_return_segment`` - Return segment to a region + +- ``rtems_region_get_segment_size`` - Obtain size of a segment + +- ``rtems_region_resize_segment`` - Change size of a segment + +Background +========== + +Region Manager Definitions +-------------------------- +.. index:: region, definition +.. index:: segment, definition + +A region makes up a physically contiguous memory +space with user-defined boundaries from which variable-sized +segments are dynamically allocated and deallocated. A segment +is a variable size section of memory which is allocated in +multiples of a user-defined page size. This page size is +required to be a multiple of four greater than or equal to four. +For example, if a request for a 350-byte segment is made in a +region with 256-byte pages, then a 512-byte segment is allocated. + +Regions are organized as doubly linked chains of +variable sized memory blocks. Memory requests are allocated +using a first-fit algorithm. If available, the requester +receives the number of bytes requested (rounded up to the next +page size). RTEMS requires some overhead from the region’s +memory for each segment that is allocated. Therefore, an +application should only modify the memory of a segment that has +been obtained from the region. The application should NOT +modify the memory outside of any obtained segments and within +the region’s boundaries while the region is currently active in +the system. + +Upon return to the region, the free block is +coalesced with its neighbors (if free) on both sides to produce +the largest possible unused block. + +Building an Attribute Set +------------------------- +.. index:: region attribute set, building + +In general, an attribute set is built by a bitwise OR +of the desired attribute components. The set of valid region +attributes is provided in the following table: + +- ``RTEMS_FIFO`` - tasks wait by FIFO (default) + +- ``RTEMS_PRIORITY`` - tasks wait by priority + +Attribute values are specifically designed to be +mutually exclusive, therefore bitwise OR and addition operations +are equivalent as long as each attribute appears exactly once in +the component list. An attribute listed as a default is not +required to appear in the attribute list, although it is a good +programming practice to specify default attributes. If all +defaults are desired, the attribute``RTEMS_DEFAULT_ATTRIBUTES`` should be +specified on this call. + +This example demonstrates the attribute_set parameter +needed to create a region with the task priority waiting queue +discipline. The attribute_set parameter to the``rtems_region_create`` +directive should be ``RTEMS_PRIORITY``. + +Building an Option Set +---------------------- + +In general, an option is built by a bitwise OR of the +desired option components. The set of valid options for the``rtems_region_get_segment`` directive are +listed in the following table: + +- ``RTEMS_WAIT`` - task will wait for segment (default) + +- ``RTEMS_NO_WAIT`` - task should not wait + +Option values are specifically designed to be +mutually exclusive, therefore bitwise OR and addition operations +are equivalent as long as each option appears exactly once in +the component list. An option listed as a default is not +required to appear in the option list, although it is a good +programming practice to specify default options. If all +defaults are desired, the option``RTEMS_DEFAULT_OPTIONS`` should be +specified on this call. + +This example demonstrates the option parameter needed +to poll for a segment. The option parameter passed to the``rtems_region_get_segment`` directive should +be ``RTEMS_NO_WAIT``. + +Operations +========== + +Creating a Region +----------------- + +The ``rtems_region_create`` directive creates a region with the +user-defined name. The user may select FIFO or task priority as +the method for placing waiting tasks in the task wait queue. +RTEMS allocates a Region Control Block (RNCB) from the RNCB free +list to maintain the newly created region. RTEMS also generates +a unique region ID which is returned to the calling task. + +It is not possible to calculate the exact number of +bytes available to the user since RTEMS requires overhead for +each segment allocated. For example, a region with one segment +that is the size of the entire region has more available bytes +than a region with two segments that collectively are the size +of the entire region. This is because the region with one +segment requires only the overhead for one segment, while the +other region requires the overhead for two segments. + +Due to automatic coalescing, the number of segments +in the region dynamically changes. Therefore, the total +overhead required by RTEMS dynamically changes. + +Obtaining Region IDs +-------------------- + +When a region is created, RTEMS generates a unique +region ID and assigns it to the created region until it is +deleted. The region ID may be obtained by either of two +methods. First, as the result of an invocation of the``rtems_region_create`` directive, +the region ID is stored in a user +provided location. Second, the region ID may be obtained later +using the ``rtems_region_ident`` directive. +The region ID is used by other region manager directives to +access this region. + +Adding Memory to a Region +------------------------- + +The ``rtems_region_extend`` directive may be used to add memory +to an existing region. The caller specifies the size in bytes +and starting address of the memory being added. + +NOTE: Please see the release notes or RTEMS source +code for information regarding restrictions on the location of +the memory being added in relation to memory already in the +region. + +Acquiring a Segment +------------------- + +The ``rtems_region_get_segment`` directive attempts to acquire +a segment from a specified region. If the region has enough +available free memory, then a segment is returned successfully +to the caller. When the segment cannot be allocated, one of the +following situations applies: + +- By default, the calling task will wait forever to acquire the segment. + +- Specifying the ``RTEMS_NO_WAIT`` option forces + an immediate return with an error status code. + +- Specifying a timeout limits the interval the task will + wait before returning with an error status code. + +If the task waits for the segment, then it is placed +in the region’s task wait queue in either FIFO or task priority +order. All tasks waiting on a region are returned an error when +the message queue is deleted. + +Releasing a Segment +------------------- + +When a segment is returned to a region by the``rtems_region_return_segment`` directive, it is merged with its +unallocated neighbors to form the largest possible segment. The +first task on the wait queue is examined to determine if its +segment request can now be satisfied. If so, it is given a +segment and unblocked. This process is repeated until the first +task’s segment request cannot be satisfied. + +Obtaining the Size of a Segment +------------------------------- + +The ``rtems_region_get_segment_size`` directive returns the +size in bytes of the specified segment. The size returned +includes any "extra" memory included in the segment because of +rounding up to a page size boundary. + +Changing the Size of a Segment +------------------------------ + +The ``rtems_region_resize_segment`` directive is used +to change the size in bytes of the specified segment. The size may be +increased or decreased. When increasing the size of a segment, it is +possible that the request cannot be satisfied. This directive provides +functionality similar to the ``realloc()`` function in the Standard +C Library. + +Deleting a Region +----------------- + +A region can be removed from the system and returned +to RTEMS with the ``rtems_region_delete`` +directive. When a region is +deleted, its control block is returned to the RNCB free list. A +region with segments still allocated is not allowed to be +deleted. Any task attempting to do so will be returned an +error. As a result of this directive, all tasks blocked waiting +to obtain a segment from the region will be readied and returned +a status code which indicates that the region was deleted. + +Directives +========== + +This section details the region manager’s directives. +A subsection is dedicated to each of this manager’s directives +and describes the calling sequence, related constants, usage, +and status codes. + +REGION_CREATE - Create a region +------------------------------- +.. index:: create a region + +**CALLING SEQUENCE:** + +.. index:: rtems_region_create + +.. code:: c + + rtems_status_code rtems_region_create( + rtems_name name, + void \*starting_address, + intptr_t length, + uint32_t page_size, + rtems_attribute attribute_set, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - region created successfully +``RTEMS_INVALID_NAME`` - invalid region name +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``starting_address`` is NULL +``RTEMS_INVALID_ADDRESS`` - address not on four byte boundary +``RTEMS_TOO_MANY`` - too many regions created +``RTEMS_INVALID_SIZE`` - invalid page size + +**DESCRIPTION:** + +This directive creates a region from a physically +contiguous memory space which starts at starting_address and is +length bytes long. Segments allocated from the region will be a +multiple of page_size bytes in length. The assigned region id +is returned in id. This region id is used as an argument to +other region related directives to access the region. + +For control and maintenance of the region, RTEMS +allocates and initializes an RNCB from the RNCB free pool. Thus +memory from the region is not used to store the RNCB. However, +some overhead within the region is required by RTEMS each time a +segment is constructed in the region. + +Specifying ``RTEMS_PRIORITY`` in attribute_set causes tasks +waiting for a segment to be serviced according to task priority. +Specifying ``RTEMS_FIFO`` in attribute_set or selecting``RTEMS_DEFAULT_ATTRIBUTES`` will cause waiting tasks to +be serviced in First In-First Out order. + +The ``starting_address`` parameter must be aligned on a +four byte boundary. The ``page_size`` parameter must be a multiple +of four greater than or equal to eight. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +The following region attribute constants are defined +by RTEMS: + +- ``RTEMS_FIFO`` - tasks wait by FIFO (default) + +- ``RTEMS_PRIORITY`` - tasks wait by priority + +REGION_IDENT - Get ID of a region +--------------------------------- +.. index:: get ID of a region +.. index:: obtain ID of a region + +**CALLING SEQUENCE:** + +.. index:: rtems_region_ident + +.. code:: c + + rtems_status_code rtems_region_ident( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - region identified successfully +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - region name not found + +**DESCRIPTION:** + +This directive obtains the region id associated with +the region name to be acquired. If the region name is not +unique, then the region id will match one of the regions with +that name. However, this region id is not guaranteed to +correspond to the desired region. The region id is used to +access this region in other region manager directives. + +**NOTES:** + +This directive will not cause the running task to be preempted. + +REGION_DELETE - Delete a region +------------------------------- +.. index:: delete a region + +**CALLING SEQUENCE:** + +.. index:: rtems_region_delete + +.. code:: c + + rtems_status_code rtems_region_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - region deleted successfully +``RTEMS_INVALID_ID`` - invalid region id +``RTEMS_RESOURCE_IN_USE`` - segments still in use + +**DESCRIPTION:** + +This directive deletes the region specified by id. +The region cannot be deleted if any of its segments are still +allocated. The RNCB for the deleted region is reclaimed by +RTEMS. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +The calling task does not have to be the task that +created the region. Any local task that knows the region id can +delete the region. + +REGION_EXTEND - Add memory to a region +-------------------------------------- +.. index:: add memory to a region +.. index:: region, add memory + +**CALLING SEQUENCE:** + +.. index:: rtems_region_extend + +.. code:: c + + rtems_status_code rtems_region_extend( + rtems_id id, + void \*starting_address, + intptr_t length + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - region extended successfully +``RTEMS_INVALID_ADDRESS`` - ``starting_address`` is NULL +``RTEMS_INVALID_ID`` - invalid region id +``RTEMS_INVALID_ADDRESS`` - invalid address of area to add + +**DESCRIPTION:** + +This directive adds the memory which starts at +starting_address for length bytes to the region specified by id. + +**NOTES:** + +This directive will not cause the calling task to be preempted. + +The calling task does not have to be the task that +created the region. Any local task that knows the region id can +extend the region. + +REGION_GET_SEGMENT - Get segment from a region +---------------------------------------------- +.. index:: get segment from region + +**CALLING SEQUENCE:** + +.. index:: rtems_region_get_segment + +.. code:: c + + rtems_status_code rtems_region_get_segment( + rtems_id id, + intptr_t size, + rtems_option option_set, + rtems_interval timeout, + void \**segment + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - segment obtained successfully +``RTEMS_INVALID_ADDRESS`` - ``segment`` is NULL +``RTEMS_INVALID_ID`` - invalid region id +``RTEMS_INVALID_SIZE`` - request is for zero bytes or exceeds +the size of maximum segment which is possible for this region +``RTEMS_UNSATISFIED`` - segment of requested size not available +``RTEMS_TIMEOUT`` - timed out waiting for segment +``RTEMS_OBJECT_WAS_DELETED`` - region deleted while waiting + +**DESCRIPTION:** + +This directive obtains a variable size segment from +the region specified by id. The address of the allocated +segment is returned in segment. The ``RTEMS_WAIT`` +and ``RTEMS_NO_WAIT`` components +of the options parameter are used to specify whether the calling +tasks wish to wait for a segment to become available or return +immediately if no segment is available. For either option, if a +sufficiently sized segment is available, then the segment is +successfully acquired by returning immediately with the``RTEMS_SUCCESSFUL`` status code. + +If the calling task chooses to return immediately and +a segment large enough is not available, then an error code +indicating this fact is returned. If the calling task chooses +to wait for the segment and a segment large enough is not +available, then the calling task is placed on the region’s +segment wait queue and blocked. If the region was created with +the ``RTEMS_PRIORITY`` option, then the calling +task is inserted into the +wait queue according to its priority. However, if the region +was created with the ``RTEMS_FIFO`` option, then the calling +task is placed at the rear of the wait queue. + +The timeout parameter specifies the maximum interval +that a task is willing to wait to obtain a segment. If timeout +is set to ``RTEMS_NO_TIMEOUT``, then the +calling task will wait forever. + +**NOTES:** + +The actual length of the allocated segment may be +larger than the requested size because a segment size is always +a multiple of the region’s page size. + +The following segment acquisition option constants +are defined by RTEMS: + +- ``RTEMS_WAIT`` - task will wait for segment (default) + +- ``RTEMS_NO_WAIT`` - task should not wait + +A clock tick is required to support the timeout functionality of +this directive. + +REGION_RETURN_SEGMENT - Return segment to a region +-------------------------------------------------- +.. index:: return segment to region + +**CALLING SEQUENCE:** + +.. index:: rtems_region_return_segment + +.. code:: c + + rtems_status_code rtems_region_return_segment( + rtems_id id, + void \*segment + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - segment returned successfully +``RTEMS_INVALID_ADDRESS`` - ``segment`` is NULL +``RTEMS_INVALID_ID`` - invalid region id +``RTEMS_INVALID_ADDRESS`` - segment address not in region + +**DESCRIPTION:** + +This directive returns the segment specified by +segment to the region specified by id. The returned segment is +merged with its neighbors to form the largest possible segment. +The first task on the wait queue is examined to determine if its +segment request can now be satisfied. If so, it is given a +segment and unblocked. This process is repeated until the first +task’s segment request cannot be satisfied. + +**NOTES:** + +This directive will cause the calling task to be +preempted if one or more local tasks are waiting for a segment +and the following conditions exist: + +- a waiting task has a higher priority than the calling task + +- the size of the segment required by the waiting task + is less than or equal to the size of the segment returned. + +REGION_GET_SEGMENT_SIZE - Obtain size of a segment +-------------------------------------------------- +.. index:: get size of segment + +**CALLING SEQUENCE:** + +.. index:: rtems_region_get_segment_size + +.. code:: c + + rtems_status_code rtems_region_get_segment_size( + rtems_id id, + void \*segment, + ssize_t \*size + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - segment obtained successfully +``RTEMS_INVALID_ADDRESS`` - ``segment`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``size`` is NULL +``RTEMS_INVALID_ID`` - invalid region id +``RTEMS_INVALID_ADDRESS`` - segment address not in region + +**DESCRIPTION:** + +This directive obtains the size in bytes of the specified segment. + +**NOTES:** + +The actual length of the allocated segment may be +larger than the requested size because a segment size is always +a multiple of the region’s page size. + +REGION_RESIZE_SEGMENT - Change size of a segment +------------------------------------------------ +.. index:: resize segment + +**CALLING SEQUENCE:** + +.. index:: rtems_region_resize_segment + +.. code:: c + + rtems_status_code rtems_region_resize_segment( + rtems_id id, + void \*segment, + ssize_t size, + ssize_t \*old_size + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - segment obtained successfully +``RTEMS_INVALID_ADDRESS`` - ``segment`` is NULL +``RTEMS_INVALID_ADDRESS`` - ``old_size`` is NULL +``RTEMS_INVALID_ID`` - invalid region id +``RTEMS_INVALID_ADDRESS`` - segment address not in region``RTEMS_UNSATISFIED`` - unable to make segment larger + +**DESCRIPTION:** + +This directive is used to increase or decrease the size of +a segment. When increasing the size of a segment, it +is possible that there is not memory available contiguous +to the segment. In this case, the request is unsatisfied. + +**NOTES:** + +If an attempt to increase the size of a segment fails, then +the application may want to allocate a new segment of the desired +size, copy the contents of the original segment to the new, larger +segment and then return the original segment. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Dual-Ported Memory Manager +########################## + +.. index:: ports +.. index:: dual ported memory + +Introduction +============ + +The dual-ported memory manager provides a mechanism +for converting addresses between internal and external +representations for multiple dual-ported memory areas (DPMA). +The directives provided by the dual-ported memory manager are: + +- ``rtems_port_create`` - Create a port + +- ``rtems_port_ident`` - Get ID of a port + +- ``rtems_port_delete`` - Delete a port + +- ``rtems_port_external_to_internal`` - Convert external to internal address + +- ``rtems_port_internal_to_external`` - Convert internal to external address + +Background +========== +.. index:: dual ported memory, definition +.. index:: external addresses, definition +.. index:: internal addresses, definition + +A dual-ported memory area (DPMA) is an contiguous +block of RAM owned by a particular processor but which can be +accessed by other processors in the system. The owner accesses +the memory using internal addresses, while other processors must +use external addresses. RTEMS defines a port as a particular +mapping of internal and external addresses. + +There are two system configurations in which +dual-ported memory is commonly found. The first is +tightly-coupled multiprocessor computer systems where the +dual-ported memory is shared between all nodes and is used for +inter-node communication. The second configuration is computer +systems with intelligent peripheral controllers. These +controllers typically utilize the DPMA for high-performance data +transfers. + +Operations +========== + +Creating a Port +--------------- + +The ``rtems_port_create`` directive creates a port into a DPMA +with the user-defined name. The user specifies the association +between internal and external representations for the port being +created. RTEMS allocates a Dual-Ported Memory Control Block +(DPCB) from the DPCB free list to maintain the newly created +DPMA. RTEMS also generates a unique dual-ported memory port ID +which is returned to the calling task. RTEMS does not +initialize the dual-ported memory area or access any memory +within it. + +Obtaining Port IDs +------------------ + +When a port is created, RTEMS generates a unique port +ID and assigns it to the created port until it is deleted. The +port ID may be obtained by either of two methods. First, as the +result of an invocation of the``rtems_port_create`` directive, the task +ID is stored in a user provided location. Second, the port ID +may be obtained later using the``rtems_port_ident`` directive. The port +ID is used by other dual-ported memory manager directives to +access this port. + +Converting an Address +--------------------- + +The ``rtems_port_external_to_internal`` directive is used to +convert an address from external to internal representation for +the specified port. +The ``rtems_port_internal_to_external`` directive is +used to convert an address from internal to external +representation for the specified port. If an attempt is made to +convert an address which lies outside the specified DPMA, then +the address to be converted will be returned. + +Deleting a DPMA Port +-------------------- + +A port can be removed from the system and returned to +RTEMS with the ``rtems_port_delete`` directive. When a port is deleted, +its control block is returned to the DPCB free list. + +Directives +========== + +This section details the dual-ported memory manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +PORT_CREATE - Create a port +--------------------------- +.. index:: create a port + +**CALLING SEQUENCE:** + +.. index:: rtems_port_create + +.. code:: c + + rtems_status_code rtems_port_create( + rtems_name name, + void \*internal_start, + void \*external_start, + uint32_t length, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - port created successfully +``RTEMS_INVALID_NAME`` - invalid port name +``RTEMS_INVALID_ADDRESS`` - address not on four byte boundary +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_TOO_MANY`` - too many DP memory areas created + +**DESCRIPTION:** + +This directive creates a port which resides on the +local node for the specified DPMA. The assigned port id is +returned in id. This port id is used as an argument to other +dual-ported memory manager directives to convert addresses +within this DPMA. + +For control and maintenance of the port, RTEMS +allocates and initializes an DPCB from the DPCB free pool. Thus +memory from the dual-ported memory area is not used to store the +DPCB. + +**NOTES:** + +The internal_address and external_address parameters +must be on a four byte boundary. + +This directive will not cause the calling task to be +preempted. + +PORT_IDENT - Get ID of a port +----------------------------- +.. index:: get ID of a port +.. index:: obtain ID of a port + +**CALLING SEQUENCE:** + +.. index:: rtems_port_ident + +.. code:: c + + rtems_status_code rtems_port_ident( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - port identified successfully +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - port name not found + +**DESCRIPTION:** + +This directive obtains the port id associated with +the specified name to be acquired. If the port name is not +unique, then the port id will match one of the DPMAs with that +name. However, this port id is not guaranteed to correspond to +the desired DPMA. The port id is used to access this DPMA in +other dual-ported memory area related directives. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +PORT_DELETE - Delete a port +--------------------------- +.. index:: delete a port + +**CALLING SEQUENCE:** + +.. index:: rtems_port_delete + +.. code:: c + + rtems_status_code rtems_port_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - port deleted successfully +``RTEMS_INVALID_ID`` - invalid port id + +**DESCRIPTION:** + +This directive deletes the dual-ported memory area +specified by id. The DPCB for the deleted dual-ported memory +area is reclaimed by RTEMS. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +The calling task does not have to be the task that +created the port. Any local task that knows the port id can +delete the port. + +PORT_EXTERNAL_TO_INTERNAL - Convert external to internal address +---------------------------------------------------------------- +.. index:: convert external to internal address + +**CALLING SEQUENCE:** + +.. index:: rtems_port_external_to_internal + +.. code:: c + + rtems_status_code rtems_port_external_to_internal( + rtems_id id, + void \*external, + void \**internal + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_INVALID_ADDRESS`` - ``internal`` is NULL +``RTEMS_SUCCESSFUL`` - successful conversion + +**DESCRIPTION:** + +This directive converts a dual-ported memory address +from external to internal representation for the specified port. +If the given external address is invalid for the specified +port, then the internal address is set to the given external +address. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the calling task to be +preempted. + +PORT_INTERNAL_TO_EXTERNAL - Convert internal to external address +---------------------------------------------------------------- +.. index:: convert internal to external address + +**CALLING SEQUENCE:** + +.. index:: rtems_port_internal_to_external + +.. code:: c + + rtems_status_code rtems_port_internal_to_external( + rtems_id id, + void \*internal, + void \**external + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_INVALID_ADDRESS`` - ``external`` is NULL +``RTEMS_SUCCESSFUL`` - successful conversion + +**DESCRIPTION:** + +This directive converts a dual-ported memory address +from internal to external representation so that it can be +passed to owner of the DPMA represented by the specified port. +If the given internal address is an invalid dual-ported address, +then the external address is set to the given internal address. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the calling task to be +preempted. + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +I/O Manager +########### + +.. index:: device drivers +.. index:: IO Manager + +Introduction +============ + +The input/output interface manager provides a +well-defined mechanism for accessing device drivers and a +structured methodology for organizing device drivers. The +directives provided by the I/O manager are: + +- ``rtems_io_initialize`` - Initialize a device driver + +- ``rtems_io_register_driver`` - Register a device driver + +- ``rtems_io_unregister_driver`` - Unregister a device driver + +- ``rtems_io_register_name`` - Register a device name + +- ``rtems_io_lookup_name`` - Look up a device name + +- ``rtems_io_open`` - Open a device + +- ``rtems_io_close`` - Close a device + +- ``rtems_io_read`` - Read from a device + +- ``rtems_io_write`` - Write to a device + +- ``rtems_io_control`` - Special device services + +Background +========== + +Device Driver Table +------------------- +.. index:: Device Driver Table + +Each application utilizing the RTEMS I/O manager must specify the +address of a Device Driver Table in its Configuration Table. This table +contains each device driver’s entry points that is to be initialised by +RTEMS during initialization. Each device driver may contain the +following entry points: + +- Initialization + +- Open + +- Close + +- Read + +- Write + +- Control + +If the device driver does not support a particular +entry point, then that entry in the Configuration Table should +be NULL. RTEMS will return``RTEMS_SUCCESSFUL`` as the executive’s and +zero (0) as the device driver’s return code for these device +driver entry points. + +Applications can register and unregister drivers with the RTEMS I/O +manager avoiding the need to have all drivers statically defined and +linked into this table. + +The :file:`confdefs.h` entry ``CONFIGURE_MAXIMUM_DRIVERS`` configures +the number of driver slots available to the application. + +Major and Minor Device Numbers +------------------------------ +.. index:: major device number +.. index:: minor device number + +Each call to the I/O manager must provide a device’s +major and minor numbers as arguments. The major number is the +index of the requested driver’s entry points in the Device +Driver Table, and is used to select a specific device driver. +The exact usage of the minor number is driver specific, but is +commonly used to distinguish between a number of devices +controlled by the same driver... index:: rtems_device_major_number +.. index:: rtems_device_minor_number + +The data types ``rtems_device_major_number`` and``rtems_device_minor_number`` are used to +manipulate device major and minor numbers, respectively. + +Device Names +------------ +.. index:: device names + +The I/O Manager provides facilities to associate a +name with a particular device. Directives are provided to +register the name of a device and to look up the major/minor +number pair associated with a device name. + +Device Driver Environment +------------------------- + +Application developers, as well as device driver +developers, must be aware of the following regarding the RTEMS +I/O Manager: + +- A device driver routine executes in the context of the + invoking task. Thus if the driver blocks, the invoking task + blocks. + +- The device driver is free to change the modes of the + invoking task, although the driver should restore them to their + original values. + +- Device drivers may be invoked from ISRs. + +- Only local device drivers are accessible through the I/O + manager. + +- A device driver routine may invoke all other RTEMS + directives, including I/O directives, on both local and global + objects. + +Although the RTEMS I/O manager provides a framework +for device drivers, it makes no assumptions regarding the +construction or operation of a device driver. + +Runtime Driver Registration +--------------------------- +.. index:: runtime driver registration + +Board support package and application developers can select wether a +device driver is statically entered into the default device table or +registered at runtime. + +Dynamic registration helps applications where: + +# The BSP and kernel libraries are common to a range of applications + for a specific target platform. An application may be built upon a + common library with all drivers. The application selects and registers + the drivers. Uniform driver name lookup protects the application. + +# The type and range of drivers may vary as the application probes a + bus during initialization. + +# Support for hot swap bus system such as Compact PCI. + +# Support for runtime loadable driver modules. + +Device Driver Interface +----------------------- +.. index:: device driver interface + +When an application invokes an I/O manager directive, +RTEMS determines which device driver entry point must be +invoked. The information passed by the application to RTEMS is +then passed to the correct device driver entry point. RTEMS +will invoke each device driver entry point assuming it is +compatible with the following prototype: +.. code:: c + + rtems_device_driver io_entry( + rtems_device_major_number major, + rtems_device_minor_number minor, + void \*argument_block + ); + +The format and contents of the parameter block are +device driver and entry point dependent. + +It is recommended that a device driver avoid +generating error codes which conflict with those used by +application components. A common technique used to generate +driver specific error codes is to make the most significant part +of the status indicate a driver specific code. + +Device Driver Initialization +---------------------------- + +RTEMS automatically initializes all device drivers +when multitasking is initiated via the``rtems_initialize_executive`` +directive. RTEMS initializes the device drivers by invoking +each device driver initialization entry point with the following +parameters: + +major + the major device number for this device driver. + +minor + zero. + +argument_block + will point to the Configuration Table. + +The returned status will be ignored by RTEMS. If the driver +cannot successfully initialize the device, then it should invoke +the fatal_error_occurred directive. + +Operations +========== + +Register and Lookup Name +------------------------ + +The ``rtems_io_register`` directive associates a name with the +specified device (i.e. major/minor number pair). Device names +are typically registered as part of the device driver +initialization sequence. The ``rtems_io_lookup`` +directive is used to +determine the major/minor number pair associated with the +specified device name. The use of these directives frees the +application from being dependent on the arbitrary assignment of +major numbers in a particular application. No device naming +conventions are dictated by RTEMS. + +Accessing an Device Driver +-------------------------- + +The I/O manager provides directives which enable the +application program to utilize device drivers in a standard +manner. There is a direct correlation between the RTEMS I/O +manager directives``rtems_io_initialize``,``rtems_io_open``,``rtems_io_close``,``rtems_io_read``,``rtems_io_write``, and``rtems_io_control`` +and the underlying device driver entry points. + +Directives +========== + +This section details the I/O manager’s directives. A +subsection is dedicated to each of this manager’s directives and +describes the calling sequence, related constants, usage, and +status codes. + +IO_REGISTER_DRIVER - Register a device driver +--------------------------------------------- +.. index:: register a device driver + +**CALLING SEQUENCE:** + +.. index:: rtems_io_register_driver + +.. code:: c + + rtems_status_code rtems_io_register_driver( + rtems_device_major_number major, + rtems_driver_address_table \*driver_table, + rtems_device_major_number \*registered_major + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully registered +``RTEMS_INVALID_ADDRESS`` - invalid registered major pointer +``RTEMS_INVALID_ADDRESS`` - invalid driver table +``RTEMS_INVALID_NUMBER`` - invalid major device number +``RTEMS_TOO_MANY`` - no available major device table slot +``RTEMS_RESOURCE_IN_USE`` - major device number entry in use + +**DESCRIPTION:** + +This directive attempts to add a new device driver to the Device Driver +Table. The user can specify a specific major device number via the +directive’s ``major`` parameter, or let the registration routine find +the next available major device number by specifing a major number of``0``. The selected major device number is returned via the``registered_major`` directive parameter. The directive automatically +allocation major device numbers from the highest value down. + +This directive automatically invokes the IO_INITIALIZE directive if +the driver address table has an initialization and open entry. + +The directive returns RTEMS_TOO_MANY if Device Driver Table is +full, and RTEMS_RESOURCE_IN_USE if a specific major device +number is requested and it is already in use. + +**NOTES:** + +The Device Driver Table size is specified in the Configuration Table +condiguration. This needs to be set to maximum size the application +requires. + +IO_UNREGISTER_DRIVER - Unregister a device driver +------------------------------------------------- +.. index:: unregister a device driver + +**CALLING SEQUENCE:** + +.. index:: rtems_io_unregister_driver + +.. code:: c + + rtems_status_code rtems_io_unregister_driver( + rtems_device_major_number major + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully registered +``RTEMS_INVALID_NUMBER`` - invalid major device number + +**DESCRIPTION:** + +This directive removes a device driver from the Device Driver Table. + +**NOTES:** + +Currently no specific checks are made and the driver is not closed. + +IO_INITIALIZE - Initialize a device driver +------------------------------------------ +.. index:: initialize a device driver + +**CALLING SEQUENCE:** + +.. index:: rtems_io_initialize + +.. code:: c + + rtems_status_code rtems_io_initialize( + rtems_device_major_number major, + rtems_device_minor_number minor, + void \*argument + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully initialized +``RTEMS_INVALID_NUMBER`` - invalid major device number + +**DESCRIPTION:** + +This directive calls the device driver initialization +routine specified in the Device Driver Table for this major +number. This directive is automatically invoked for each device +driver when multitasking is initiated via the +initialize_executive directive. + +A device driver initialization module is responsible +for initializing all hardware and data structures associated +with a device. If necessary, it can allocate memory to be used +during other operations. + +**NOTES:** + +This directive may or may not cause the calling task +to be preempted. This is dependent on the device driver being +initialized. + +IO_REGISTER_NAME - Register a device +------------------------------------ +.. index:: register device + +**CALLING SEQUENCE:** + +.. index:: rtems_io_register_name + +.. code:: c + + rtems_status_code rtems_io_register_name( + const char \*name, + rtems_device_major_number major, + rtems_device_minor_number minor + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully initialized +``RTEMS_TOO_MANY`` - too many devices registered + +**DESCRIPTION:** + +This directive associates name with the specified +major/minor number pair. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +IO_LOOKUP_NAME - Lookup a device +-------------------------------- +.. index:: lookup device major and minor number + +**CALLING SEQUENCE:** + +.. index:: rtems_io_lookup_name + +.. code:: c + + rtems_status_code rtems_io_lookup_name( + const char \*name, + rtems_driver_name_t \*device_info + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully initialized +``RTEMS_UNSATISFIED`` - name not registered + +**DESCRIPTION:** + +This directive returns the major/minor number pair +associated with the given device name in ``device_info``. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +IO_OPEN - Open a device +----------------------- +.. index:: open a devive + +**CALLING SEQUENCE:** + +.. index:: rtems_io_open + +.. code:: c + + rtems_status_code rtems_io_open( + rtems_device_major_number major, + rtems_device_minor_number minor, + void \*argument + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully initialized +``RTEMS_INVALID_NUMBER`` - invalid major device number + +**DESCRIPTION:** + +This directive calls the device driver open routine +specified in the Device Driver Table for this major number. The +open entry point is commonly used by device drivers to provide +exclusive access to a device. + +**NOTES:** + +This directive may or may not cause the calling task +to be preempted. This is dependent on the device driver being +invoked. + +IO_CLOSE - Close a device +------------------------- +.. index:: close a device + +**CALLING SEQUENCE:** + +.. index:: rtems_io_close + +.. code:: c + + rtems_status_code rtems_io_close( + rtems_device_major_number major, + rtems_device_minor_number minor, + void \*argument + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully initialized +``RTEMS_INVALID_NUMBER`` - invalid major device number + +**DESCRIPTION:** + +This directive calls the device driver close routine +specified in the Device Driver Table for this major number. The +close entry point is commonly used by device drivers to +relinquish exclusive access to a device. + +**NOTES:** + +This directive may or may not cause the calling task +to be preempted. This is dependent on the device driver being +invoked. + +IO_READ - Read from a device +---------------------------- +.. index:: read from a device + +**CALLING SEQUENCE:** + +.. index:: rtems_io_read + +.. code:: c + + rtems_status_code rtems_io_read( + rtems_device_major_number major, + rtems_device_minor_number minor, + void \*argument + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully initialized +``RTEMS_INVALID_NUMBER`` - invalid major device number + +**DESCRIPTION:** + +This directive calls the device driver read routine +specified in the Device Driver Table for this major number. +Read operations typically require a buffer address as part of +the argument parameter block. The contents of this buffer will +be replaced with data from the device. + +**NOTES:** + +This directive may or may not cause the calling task +to be preempted. This is dependent on the device driver being +invoked. + +IO_WRITE - Write to a device +---------------------------- +.. index:: write to a device + +**CALLING SEQUENCE:** + +.. index:: rtems_io_write + +.. code:: c + + rtems_status_code rtems_io_write( + rtems_device_major_number major, + rtems_device_minor_number minor, + void \*argument + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully initialized +``RTEMS_INVALID_NUMBER`` - invalid major device number + +**DESCRIPTION:** + +This directive calls the device driver write routine +specified in the Device Driver Table for this major number. +Write operations typically require a buffer address as part of +the argument parameter block. The contents of this buffer will +be sent to the device. + +**NOTES:** + +This directive may or may not cause the calling task +to be preempted. This is dependent on the device driver being +invoked. + +IO_CONTROL - Special device services +------------------------------------ +.. index:: special device services +.. index:: IO Control + +**CALLING SEQUENCE:** + +.. index:: rtems_io_control + +.. code:: c + + rtems_status_code rtems_io_control( + rtems_device_major_number major, + rtems_device_minor_number minor, + void \*argument + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successfully initialized +``RTEMS_INVALID_NUMBER`` - invalid major device number + +**DESCRIPTION:** + +This directive calls the device driver I/O control +routine specified in the Device Driver Table for this major +number. The exact functionality of the driver entry called by +this directive is driver dependent. It should not be assumed +that the control entries of two device drivers are compatible. +For example, an RS-232 driver I/O control operation may change +the baud rate of a serial line, while an I/O control operation +for a floppy disk driver may cause a seek operation. + +**NOTES:** + +This directive may or may not cause the calling task +to be preempted. This is dependent on the device driver being +invoked. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Fatal Error Manager +################### + +.. index:: fatal errors + +Introduction +============ + +The fatal error manager processes all fatal or irrecoverable errors and other +sources of system termination (for example after exit()). The directives +provided by the fatal error manager are: + +- ``rtems_fatal_error_occurred`` - Invoke the fatal error handler + +- ``rtems_fatal`` - Invoke the fatal error handler with error source + +Background +========== +.. index:: fatal error detection +.. index:: fatal error processing +.. index:: fatal error user extension + +The fatal error manager is called upon detection of +an irrecoverable error condition by either RTEMS or the +application software. Fatal errors can be detected from three +sources: + +- the executive (RTEMS) + +- user system code + +- user application code + +RTEMS automatically invokes the fatal error manager +upon detection of an error it considers to be fatal. Similarly, +the user should invoke the fatal error manager upon detection of +a fatal error. + +Each static or dynamic user extension set may include +a fatal error handler. The fatal error handler in the static +extension set can be used to provide access to debuggers and +monitors which may be present on the target hardware. If any +user-supplied fatal error handlers are installed, the fatal +error manager will invoke them. If no user handlers are +configured or if all the user handler return control to the +fatal error manager, then the RTEMS default fatal error handler +is invoked. If the default fatal error handler is invoked, then +the system state is marked as failed. + +Although the precise behavior of the default fatal +error handler is processor specific, in general, it will disable +all maskable interrupts, place the error code in a known +processor dependent place (generally either on the stack or in a +register), and halt the processor. The precise actions of the +RTEMS fatal error are discussed in the Default Fatal Error +Processing chapter of the Applications Supplement document for +a specific target processor. + +Operations +========== + + +Announcing a Fatal Error +------------------------ +.. index:: _Internal_errors_What_happened + +The ``rtems_fatal_error_occurred`` directive is invoked when a +fatal error is detected. Before invoking any user-supplied +fatal error handlers or the RTEMS fatal error handler, the``rtems_fatal_error_occurred`` +directive stores useful information in the +variable ``_Internal_errors_What_happened``. This structure +contains three pieces of information: + +- the source of the error (API or executive core), + +- whether the error was generated internally by the + executive, and a + +- a numeric code to indicate the error type. + +The error type indicator is dependent on the source +of the error and whether or not the error was internally +generated by the executive. If the error was generated +from an API, then the error code will be of that API’s +error or status codes. The status codes for the RTEMS +API are in cpukit/rtems/include/rtems/rtems/status.h. Those +for the POSIX API can be found in . + +The ``rtems_fatal_error_occurred`` directive is responsible +for invoking an optional user-supplied fatal error handler +and/or the RTEMS fatal error handler. All fatal error handlers +are passed an error code to describe the error detected. + +Occasionally, an application requires more +sophisticated fatal error processing such as passing control to +a debugger. For these cases, a user-supplied fatal error +handler can be specified in the RTEMS configuration table. The +User Extension Table field fatal contains the address of the +fatal error handler to be executed when the``rtems_fatal_error_occurred`` +directive is called. If the field is set to NULL or if the +configured fatal error handler returns to the executive, then +the default handler provided by RTEMS is executed. This default +handler will halt execution on the processor where the error +occurred. + +Directives +========== + +This section details the fatal error manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +FATAL_ERROR_OCCURRED - Invoke the fatal error handler +----------------------------------------------------- +.. index:: announce fatal error +.. index:: fatal error, announce + +**CALLING SEQUENCE:** + +.. index:: rtems_fatal_error_occurred + +.. code:: c + + void rtems_fatal_error_occurred( + uint32_t the_error + ); + +**DIRECTIVE STATUS CODES** + +NONE + +**DESCRIPTION:** + +This directive processes fatal errors. If the FATAL +error extension is defined in the configuration table, then the +user-defined error extension is called. If configured and the +provided FATAL error extension returns, then the RTEMS default +error handler is invoked. This directive can be invoked by +RTEMS or by the user’s application code including initialization +tasks, other tasks, and ISRs. + +**NOTES:** + +This directive supports local operations only. + +Unless the user-defined error extension takes special +actions such as restarting the calling task, this directive WILL +NOT RETURN to the caller. + +The user-defined extension for this directive may +wish to initiate a global shutdown. + +FATAL - Invoke the fatal error handler with error source +-------------------------------------------------------- +.. index:: announce fatal error +.. index:: fatal error, announce + +**CALLING SEQUENCE:** + +.. index:: rtems_fatal + +.. code:: c + + void rtems_fatal( + rtems_fatal_source source, + rtems_fatal_code error + ); + +**DIRECTIVE STATUS CODES** + +NONE + +**DESCRIPTION:** + +This directive invokes the internal error handler with is internal set to +false. See also ``rtems_fatal_error_occurred``. + +EXCEPTION_FRAME_PRINT - Prints the exception frame +-------------------------------------------------- +.. index:: exception frame + +**CALLING SEQUENCE:** + +.. index:: rtems_exception_frame_print + +.. code:: c + + void rtems_exception_frame_print( + const rtems_exception_frame \*frame + ); + +**DIRECTIVE STATUS CODES** + +NONE + +**DESCRIPTION:** + +Prints the exception frame via printk(). + +FATAL_SOURCE_TEXT - Returns a text for a fatal source +----------------------------------------------------- +.. index:: fatal error + +**CALLING SEQUENCE:** + +.. index:: rtems_fatal_source_text + +.. code:: c + + const char \*rtems_fatal_source_text( + rtems_fatal_source source + ); + +**DIRECTIVE STATUS CODES** + +The fatal source text or "?" in case the passed fatal source is invalid. + +**DESCRIPTION:** + +Returns a text for a fatal source. The text for fatal source is the enumerator +constant. + +INTERNAL_ERROR_TEXT - Returns a text for an internal error code +--------------------------------------------------------------- +.. index:: fatal error + +**CALLING SEQUENCE:** + +.. index:: rtems_internal_error_text + +.. code:: c + + const char \*rtems_internal_error_text( + rtems_fatal_code error + ); + +**DIRECTIVE STATUS CODES** + +The error code text or "?" in case the passed error code is invalid. + +**DESCRIPTION:** + +Returns a text for an internal error code. The text for each internal error +code is the enumerator constant. + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Board Support Packages +###################### + +.. index:: Board Support Packages +.. index:: BSPs + +Introduction +============ +.. index:: BSP, definition + +A board support package (BSP) is a collection of +user-provided facilities which interface RTEMS and an +application with a specific hardware platform. These facilities +may include hardware initialization, device drivers, user +extensions, and a Multiprocessor Communications Interface +(MPCI). However, a minimal BSP need only support processor +reset and initialization and, if needed, a clock tick. + +Reset and Initialization +======================== + +An RTEMS based application is initiated or +re-initiated when the processor is reset. This initialization +code is responsible for preparing the target platform for the +RTEMS application. Although the exact actions performed by the +initialization code are highly processor and target dependent, +the logical functionality of these actions are similar across a +variety of processors and target platforms. + +Normally, the BSP and some of the application initialization is +intertwined in the RTEMS initialization sequence controlled by +the shared function ``boot_card()``. + +The reset application initialization code is executed +first when the processor is reset. All of the hardware must be +initialized to a quiescent state by this software before +initializing RTEMS. When in quiescent state, devices do not +generate any interrupts or require any servicing by the +application. Some of the hardware components may be initialized +in this code as well as any application initialization that does +not involve calls to RTEMS directives. + +The processor’s Interrupt Vector Table which will be used by the +application may need to be set to the required value by the reset +application initialization code. Because interrupts are enabled +automatically by RTEMS as part of the context switch to the first task, +the Interrupt Vector Table MUST be set before this directive is invoked +to ensure correct interrupt vectoring. The processor’s Interrupt Vector +Table must be accessible by RTEMS as it will be modified by the when +installing user Interrupt Service Routines (ISRs) On some CPUs, RTEMS +installs it’s own Interrupt Vector Table as part of initialization and +thus these requirements are met automatically. The reset code which is +executed before the call to any RTEMS initialization routines has the +following requirements: + +- Must not make any blocking RTEMS directive calls. + +- If the processor supports multiple privilege levels, must leave + the processor in the most privileged, or supervisory, state. + +- Must allocate a stack of sufficient size to execute the initialization + and shutdown of the system. This stack area will NOT be used by any task + once the system is initialized. This stack is often reserved via the + linker script or in the assembly language start up file. + +- Must initialize the stack pointer for the initialization process to + that allocated. + +- Must initialize the processor’s Interrupt Vector Table. + +- Must disable all maskable interrupts. + +- If the processor supports a separate interrupt stack, must allocate + the interrupt stack and initialize the interrupt stack pointer. + +At the end of the initialization sequence, RTEMS does not return to the +BSP initialization code, but instead context switches to the highest +priority task to begin application execution. This task is typically +a User Initialization Task which is responsible for performing both +local and global application initialization which is dependent on RTEMS +facilities. It is also responsible for initializing any higher level +RTEMS services the application uses such as networking and blocking +device drivers. + +Interrupt Stack Requirements +---------------------------- + +The worst-case stack usage by interrupt service +routines must be taken into account when designing an +application. If the processor supports interrupt nesting, the +stack usage must include the deepest nest level. The worst-case +stack usage must account for the following requirements: + +- Processor’s interrupt stack frame + +- Processor’s subroutine call stack frame + +- RTEMS system calls + +- Registers saved on stack + +- Application subroutine calls + +The size of the interrupt stack must be greater than or equal to the +confugured minimum stack size. + +Processors with a Separate Interrupt Stack +------------------------------------------ + +Some processors support a separate stack for interrupts. When an +interrupt is vectored and the interrupt is not nested, the processor +will automatically switch from the current stack to the interrupt stack. +The size of this stack is based solely on the worst-case stack usage by +interrupt service routines. + +The dedicated interrupt stack for the entire application on some +architectures is supplied and initialized by the reset and initialization +code of the user’s Board Support Package. Whether allocated and +initialized by the BSP or RTEMS, since all ISRs use this stack, the +stack size must take into account the worst case stack usage by any +combination of nested ISRs. + +Processors Without a Separate Interrupt Stack +--------------------------------------------- + +Some processors do not support a separate stack for interrupts. In this +case, without special assistance every task’s stack must include +enough space to handle the task’s worst-case stack usage as well as +the worst-case interrupt stack usage. This is necessary because the +worst-case interrupt nesting could occur while any task is executing. + +On many processors without dedicated hardware managed interrupt stacks, +RTEMS manages a dedicated interrupt stack in software. If this capability +is supported on a CPU, then it is logically equivalent to the processor +supporting a separate interrupt stack in hardware. + +Device Drivers +============== + +Device drivers consist of control software for +special peripheral devices and provide a logical interface for +the application developer. The RTEMS I/O manager provides +directives which allow applications to access these device +drivers in a consistent fashion. A Board Support Package may +include device drivers to access the hardware on the target +platform. These devices typically include serial and parallel +ports, counter/timer peripherals, real-time clocks, disk +interfaces, and network controllers. + +For more information on device drivers, refer to the +I/O Manager chapter. + +Clock Tick Device Driver +------------------------ + +Most RTEMS applications will include a clock tick +device driver which invokes the ``rtems_clock_tick`` +directive at regular intervals. The clock tick is necessary if +the application is to utilize timeslicing, the clock manager, the +timer manager, the rate monotonic manager, or the timeout option on blocking +directives. + +The clock tick is usually provided as an interrupt from a counter/timer +or a real-time clock device. When a counter/timer is used to provide the +clock tick, the device is typically programmed to operate in continuous +mode. This mode selection causes the device to automatically reload the +initial count and continue the countdown without programmer intervention. +This reduces the overhead required to manipulate the counter/timer in +the clock tick ISR and increases the accuracy of tick occurrences. +The initial count can be based on the microseconds_per_tick field +in the RTEMS Configuration Table. An alternate approach is to set +the initial count for a fixed time period (such as one millisecond) +and have the ISR invoke ``rtems_clock_tick`` on the +configured ``microseconds_per_tick`` boundaries. Obviously, this +can induce some error if the configured ``microseconds_per_tick`` +is not evenly divisible by the chosen clock interrupt quantum. + +It is important to note that the interval between +clock ticks directly impacts the granularity of RTEMS timing +operations. In addition, the frequency of clock ticks is an +important factor in the overall level of system overhead. A +high clock tick frequency results in less processor time being +available for task execution due to the increased number of +clock tick ISRs. + +User Extensions +=============== + +RTEMS allows the application developer to augment +selected features by invoking user-supplied extension routines +when the following system events occur: + +- Task creation + +- Task initiation + +- Task reinitiation + +- Task deletion + +- Task context switch + +- Post task context switch + +- Task begin + +- Task exits + +- Fatal error detection + +User extensions can be used to implement a wide variety of +functions including execution profiling, non-standard +coprocessor support, debug support, and error detection and +recovery. For example, the context of a non-standard numeric +coprocessor may be maintained via the user extensions. In this +example, the task creation and deletion extensions are +responsible for allocating and deallocating the context area, +the task initiation and reinitiation extensions would be +responsible for priming the context area, and the task context +switch extension would save and restore the context of the +device. + +For more information on user extensions, refer to `User Extensions Manager`_. + +Multiprocessor Communications Interface (MPCI) +============================================== + +RTEMS requires that an MPCI layer be provided when a +multiple node application is developed. This MPCI layer must +provide an efficient and reliable communications mechanism +between the multiple nodes. Tasks on different nodes +communicate and synchronize with one another via the MPCI. Each +MPCI layer must be tailored to support the architecture of the +target platform. + +For more information on the MPCI, refer to the +Multiprocessing Manager chapter. + +Tightly-Coupled Systems +----------------------- + +A tightly-coupled system is a multiprocessor +configuration in which the processors communicate solely via +shared global memory. The MPCI can simply place the RTEMS +packets in the shared memory space. The two primary +considerations when designing an MPCI for a tightly-coupled +system are data consistency and informing another node of a +packet. + +The data consistency problem may be solved using +atomic "test and set" operations to provide a "lock" in the +shared memory. It is important to minimize the length of time +any particular processor locks a shared data structure. + +The problem of informing another node of a packet can +be addressed using one of two techniques. The first technique +is to use an interprocessor interrupt capability to cause an +interrupt on the receiving node. This technique requires that +special support hardware be provided by either the processor +itself or the target platform. The second technique is to have +a node poll for arrival of packets. The drawback to this +technique is the overhead associated with polling. + +Loosely-Coupled Systems +----------------------- + +A loosely-coupled system is a multiprocessor +configuration in which the processors communicate via some type +of communications link which is not shared global memory. The +MPCI sends the RTEMS packets across the communications link to +the destination node. The characteristics of the communications +link vary widely and have a significant impact on the MPCI +layer. For example, the bandwidth of the communications link +has an obvious impact on the maximum MPCI throughput. + +The characteristics of a shared network, such as +Ethernet, lend themselves to supporting an MPCI layer. These +networks provide both the point-to-point and broadcast +capabilities which are expected by RTEMS. + +Systems with Mixed Coupling +--------------------------- + +A mixed-coupling system is a multiprocessor +configuration in which the processors communicate via both +shared memory and communications links. A unique characteristic +of mixed-coupling systems is that a node may not have access to +all communication methods. There may be multiple shared memory +areas and communication links. Therefore, one of the primary +functions of the MPCI layer is to efficiently route RTEMS +packets between nodes. This routing may be based on numerous +algorithms. In addition, the router may provide alternate +communications paths in the event of an overload or a partial +failure. + +Heterogeneous Systems +--------------------- + +Designing an MPCI layer for a heterogeneous system +requires special considerations by the developer. RTEMS is +designed to eliminate many of the problems associated with +sharing data in a heterogeneous environment. The MPCI layer +need only address the representation of thirty-two (32) bit +unsigned quantities. + +For more information on supporting a heterogeneous +system, refer the Supporting Heterogeneous Environments in the +Multiprocessing Manager chapter. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + + +User Extensions Manager +####################### + +.. index:: user extensions + +Introduction +============ + +The RTEMS User Extensions Manager allows the +application developer to augment the executive by allowing them +to supply extension routines which are invoked at critical +system events. The directives provided by the user extensions +manager are: + +- ``rtems_extension_create`` - Create an extension set + +- ``rtems_extension_ident`` - Get ID of an extension set + +- ``rtems_extension_delete`` - Delete an extension set + +Background +========== + +User extension routines are invoked when the +following system events occur: + +- Task creation + +- Task initiation + +- Task reinitiation + +- Task deletion + +- Task context switch + +- Post task context switch + +- Task begin + +- Task exits + +- Fatal error detection + +These extensions are invoked as a function with +arguments that are appropriate to the system event. + +Extension Sets +-------------- +.. index:: extension set + +An extension set is defined as a set of routines +which are invoked at each of the critical system events at which +user extension routines are invoked. Together a set of these +routines typically perform a specific functionality such as +performance monitoring or debugger support. RTEMS is informed of +the entry points which constitute an extension set via the +following structure:.. index:: rtems_extensions_table + +.. code:: c + + typedef struct { + rtems_task_create_extension thread_create; + rtems_task_start_extension thread_start; + rtems_task_restart_extension thread_restart; + rtems_task_delete_extension thread_delete; + rtems_task_switch_extension thread_switch; + rtems_task_begin_extension thread_begin; + rtems_task_exitted_extension thread_exitted; + rtems_fatal_extension fatal; + } rtems_extensions_table; + +RTEMS allows the user to have multiple extension sets +active at the same time. First, a single static extension set +may be defined as the application’s User Extension Table which +is included as part of the Configuration Table. This extension +set is active for the entire life of the system and may not be +deleted. This extension set is especially important because it +is the only way the application can provided a FATAL error +extension which is invoked if RTEMS fails during the +initialize_executive directive. The static extension set is +optional and may be configured as NULL if no static extension +set is required. + +Second, the user can install dynamic extensions using +the ``rtems_extension_create`` +directive. These extensions are RTEMS +objects in that they have a name, an ID, and can be dynamically +created and deleted. In contrast to the static extension set, +these extensions can only be created and installed after the +initialize_executive directive successfully completes execution. +Dynamic extensions are useful for encapsulating the +functionality of an extension set. For example, the application +could use extensions to manage a special coprocessor, do +performance monitoring, and to do stack bounds checking. Each +of these extension sets could be written and installed +independently of the others. + +All user extensions are optional and RTEMS places no +naming restrictions on the user. The user extension entry points +are copied into an internal RTEMS structure. This means the user +does not need to keep the table after creating it, and changing the +handler entry points dynamically in a table once created has no +effect. Creating a table local to a function can save space in +space limited applications. + +Extension switches do not effect the context switch overhead if +no switch handler is installed. + +TCB Extension Area +------------------ +.. index:: TCB extension area + +RTEMS provides for a pointer to a user-defined data +area for each extension set to be linked to each task’s control +block. This set of pointers is an extension of the TCB and can +be used to store additional data required by the user’s +extension functions. + +The TCB extension is an array of pointers in the TCB. The +index into the table can be obtained from the extension id +returned when the extension is created:.. index:: rtems extensions table index + +.. code:: c + + index = rtems_object_id_get_index(extension_id); + +The number of pointers in the area is the same as the number of +user extension sets configured. This allows an application to +augment the TCB with user-defined information. For example, an +application could implement task profiling by storing timing +statistics in the TCB’s extended memory area. When a task +context switch is being executed, the TASK_SWITCH extension +could read a real-time clock to calculate how long the task +being swapped out has run as well as timestamp the starting time +for the task being swapped in. + +If used, the extended memory area for the TCB should +be allocated and the TCB extension pointer should be set at the +time the task is created or started by either the TASK_CREATE or +TASK_START extension. The application is responsible for +managing this extended memory area for the TCBs. The memory may +be reinitialized by the TASK_RESTART extension and should be +deallocated by the TASK_DELETE extension when the task is +deleted. Since the TCB extension buffers would most likely be +of a fixed size, the RTEMS partition manager could be used to +manage the application’s extended memory area. The application +could create a partition of fixed size TCB extension buffers and +use the partition manager’s allocation and deallocation +directives to obtain and release the extension buffers. + +Extensions +---------- + +The sections that follow will contain a description +of each extension. Each section will contain a prototype of a +function with the appropriate calling sequence for the +corresponding extension. The names given for the C +function and +its arguments are all defined by the user. The names used in +the examples were arbitrarily chosen and impose no naming +conventions on the user. + +TASK_CREATE Extension +~~~~~~~~~~~~~~~~~~~~~ + +The TASK_CREATE extension directly corresponds to the``rtems_task_create`` directive. If this extension +is defined in any +static or dynamic extension set and a task is being created, +then the extension routine will automatically be invoked by +RTEMS. The extension should have a prototype similar to the +following:.. index:: rtems_task_create_extension +.. index:: rtems_extension + +.. code:: c + + bool user_task_create( + rtems_tcb \*current_task, + rtems_tcb \*new_task + ); + +where ``current_task`` can be used to access the TCB for +the currently executing task, and new_task can be used to access +the TCB for the new task being created. This extension is +invoked from the ``rtems_task_create`` +directive after ``new_task`` has been +completely initialized, but before it is placed on a ready TCB +chain. + +The user extension is expected to return the boolean +value ``true`` if it successfully executed and``false`` otherwise. A task create user extension +will frequently attempt to allocate resources. If this +allocation fails, then the extension should return``false`` and the entire task create operation +will fail. + +TASK_START Extension +~~~~~~~~~~~~~~~~~~~~ + +The TASK_START extension directly corresponds to the +task_start directive. If this extension is defined in any +static or dynamic extension set and a task is being started, +then the extension routine will automatically be invoked by +RTEMS. The extension should have a prototype similar to the +following:.. index:: rtems_task_start_extension + +.. code:: c + + void user_task_start( + rtems_tcb \*current_task, + rtems_tcb \*started_task + ); + +where current_task can be used to access the TCB for +the currently executing task, and started_task can be used to +access the TCB for the dormant task being started. This +extension is invoked from the task_start directive after +started_task has been made ready to start execution, but before +it is placed on a ready TCB chain. + +TASK_RESTART Extension +~~~~~~~~~~~~~~~~~~~~~~ + +The TASK_RESTART extension directly corresponds to +the task_restart directive. If this extension is defined in any +static or dynamic extension set and a task is being restarted, +then the extension should have a prototype similar to the +following:.. index:: rtems_task_restart_extension + +.. code:: c + + void user_task_restart( + rtems_tcb \*current_task, + rtems_tcb \*restarted_task + ); + +where current_task can be used to access the TCB for +the currently executing task, and restarted_task can be used to +access the TCB for the task being restarted. This extension is +invoked from the task_restart directive after restarted_task has +been made ready to start execution, but before it is placed on a +ready TCB chain. + +TASK_DELETE Extension +~~~~~~~~~~~~~~~~~~~~~ + +The TASK_DELETE extension is associated with the +task_delete directive. If this extension is defined in any +static or dynamic extension set and a task is being deleted, +then the extension routine will automatically be invoked by +RTEMS. The extension should have a prototype similar to the +following:.. index:: rtems_task_delete_extension + +.. code:: c + + void user_task_delete( + rtems_tcb \*current_task, + rtems_tcb \*deleted_task + ); + +where current_task can be used to access the TCB for +the currently executing task, and deleted_task can be used to +access the TCB for the task being deleted. This extension is +invoked from the task_delete directive after the TCB has been +removed from a ready TCB chain, but before all its resources +including the TCB have been returned to their respective free +pools. This extension should not call any RTEMS directives if a +task is deleting itself (current_task is equal to deleted_task). + +TASK_SWITCH Extension +~~~~~~~~~~~~~~~~~~~~~ + +The TASK_SWITCH extension corresponds to a task +context switch. If this extension is defined in any static or +dynamic extension set and a task context switch is in progress, +then the extension routine will automatically be invoked by +RTEMS. The extension should have a prototype similar to the +following:.. index:: rtems_task_switch_extension + +.. code:: c + + void user_task_switch( + rtems_tcb \*current_task, + rtems_tcb \*heir_task + ); + +where current_task can be used to access the TCB for +the task that is being swapped out, and heir_task can be used to +access the TCB for the task being swapped in. This extension is +invoked from RTEMS’ dispatcher routine after the current_task +context has been saved, but before the heir_task context has +been restored. This extension should not call any RTEMS +directives. + +TASK_BEGIN Extension +~~~~~~~~~~~~~~~~~~~~ + +The TASK_BEGIN extension is invoked when a task +begins execution. It is invoked immediately before the body of +the starting procedure and executes in the context in the task. +This user extension have a prototype similar to the following:.. index:: rtems_task_begin_extension + +.. code:: c + + void user_task_begin( + rtems_tcb \*current_task + ); + +where current_task can be used to access the TCB for +the currently executing task which has begun. The distinction +between the TASK_BEGIN and TASK_START extension is that the +TASK_BEGIN extension is executed in the context of the actual +task while the TASK_START extension is executed in the context +of the task performing the task_start directive. For most +extensions, this is not a critical distinction. + +TASK_EXITTED Extension +~~~~~~~~~~~~~~~~~~~~~~ + +The TASK_EXITTED extension is invoked when a task +exits the body of the starting procedure by either an implicit +or explicit return statement. This user extension have a +prototype similar to the following:.. index:: rtems_task_exitted_extension + +.. code:: c + + void user_task_exitted( + rtems_tcb \*current_task + ); + +where current_task can be used to access the TCB for +the currently executing task which has just exitted. + +Although exiting of task is often considered to be a +fatal error, this extension allows recovery by either restarting +or deleting the exiting task. If the user does not wish to +recover, then a fatal error may be reported. If the user does +not provide a TASK_EXITTED extension or the provided handler +returns control to RTEMS, then the RTEMS default handler will be +used. This default handler invokes the directive +fatal_error_occurred with the ``RTEMS_TASK_EXITTED`` directive status. + +FATAL Error Extension +~~~~~~~~~~~~~~~~~~~~~ + +The FATAL error extension is associated with the +fatal_error_occurred directive. If this extension is defined in +any static or dynamic extension set and the fatal_error_occurred +directive has been invoked, then this extension will be called. +This extension should have a prototype similar to the following:.. index:: rtems_fatal_extension + +.. code:: c + + void user_fatal_error( + Internal_errors_Source the_source, + bool is_internal, + uint32_t the_error + ); + +where the_error is the error code passed to the +fatal_error_occurred directive. This extension is invoked from +the fatal_error_occurred directive. + +If defined, the user’s FATAL error extension is +invoked before RTEMS’ default fatal error routine is invoked and +the processor is stopped. For example, this extension could be +used to pass control to a debugger when a fatal error occurs. +This extension should not call any RTEMS directives. + +Order of Invocation +------------------- + +When one of the critical system events occur, the +user extensions are invoked in either "forward" or "reverse" +order. Forward order indicates that the static extension set is +invoked followed by the dynamic extension sets in the order in +which they were created. Reverse order means that the dynamic +extension sets are invoked in the opposite of the order in which +they were created followed by the static extension set. By +invoking the extension sets in this order, extensions can be +built upon one another. At the following system events, the +extensions are invoked in forward order: + +- Task creation + +- Task initiation + +- Task reinitiation + +- Task deletion + +- Task context switch + +- Post task context switch + +- Task begins to execute + +At the following system events, the extensions are +invoked in reverse order: + +- Task deletion + +- Fatal error detection + +At these system events, the extensions are invoked in +reverse order to insure that if an extension set is built upon +another, the more complicated extension is invoked before the +extension set it is built upon. For example, by invoking the +static extension set last it is known that the "system" fatal +error extension will be the last fatal error extension executed. +Another example is use of the task delete extension by the +Standard C Library. Extension sets which are installed after +the Standard C Library will operate correctly even if they +utilize the C Library because the C Library’s TASK_DELETE +extension is invoked after that of the other extensions. + +Operations +========== + +Creating an Extension Set +------------------------- + +The ``rtems_extension_create`` directive creates and installs +an extension set by allocating a Extension Set Control Block +(ESCB), assigning the extension set a user-specified name, and +assigning it an extension set ID. Newly created extension sets +are immediately installed and are invoked upon the next system +even supporting an extension. + +Obtaining Extension Set IDs +--------------------------- + +When an extension set is created, RTEMS generates a +unique extension set ID and assigns it to the created extension +set until it is deleted. The extension ID may be obtained by +either of two methods. First, as the result of an invocation of +the ``rtems_extension_create`` +directive, the extension set ID is stored +in a user provided location. Second, the extension set ID may +be obtained later using the ``rtems_extension_ident`` +directive. The extension set ID is used by other directives +to manipulate this extension set. + +Deleting an Extension Set +------------------------- + +The ``rtems_extension_delete`` directive is used to delete an +extension set. The extension set’s control block is returned to +the ESCB free list when it is deleted. An extension set can be +deleted by a task other than the task which created the +extension set. Any subsequent references to the extension’s +name and ID are invalid. + +Directives +========== + +This section details the user extension manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +EXTENSION_CREATE - Create a extension set +----------------------------------------- +.. index:: create an extension set + +**CALLING SEQUENCE:** + +.. index:: rtems_extension_create + +.. code:: c + + rtems_status_code rtems_extension_create( + rtems_name name, + rtems_extensions_table \*table, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - extension set created successfully +``RTEMS_INVALID_NAME`` - invalid extension set name +``RTEMS_TOO_MANY`` - too many extension sets created + +**DESCRIPTION:** + +This directive creates a extension set. The assigned +extension set id is returned in id. This id is used to access +the extension set with other user extension manager directives. +For control and maintenance of the extension set, RTEMS +allocates an ESCB from the local ESCB free pool and initializes +it. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +EXTENSION_IDENT - Get ID of a extension set +------------------------------------------- +.. index:: get ID of an extension set +.. index:: obtain ID of an extension set + +**CALLING SEQUENCE:** + +.. index:: rtems_extension_ident + +.. code:: c + + rtems_status_code rtems_extension_ident( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - extension set identified successfully +``RTEMS_INVALID_NAME`` - extension set name not found + +**DESCRIPTION:** + +This directive obtains the extension set id +associated with the extension set name to be acquired. If the +extension set name is not unique, then the extension set id will +match one of the extension sets with that name. However, this +extension set id is not guaranteed to correspond to the desired +extension set. The extension set id is used to access this +extension set in other extension set related directives. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +EXTENSION_DELETE - Delete a extension set +----------------------------------------- +.. index:: delete an extension set + +**CALLING SEQUENCE:** + +.. index:: rtems_extension_delete + +.. code:: c + + rtems_status_code rtems_extension_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - extension set deleted successfully +``RTEMS_INVALID_ID`` - invalid extension set id + +**DESCRIPTION:** + +This directive deletes the extension set specified by +id. If the extension set is running, it is automatically +canceled. The ESCB for the deleted extension set is reclaimed +by RTEMS. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +A extension set can be deleted by a task other than +the task which created the extension set. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +.. COMMENT: COPYRIGHT (c) 1988-2015. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +.. COMMENT: TODO: + +.. COMMENT: + Ensure all macros are documented. + +.. COMMENT: + Verify which structures may actually be defined by a user + +.. COMMENT: + Add Go configuration. + +.. COMMENT: Questions: + +.. COMMENT: + Should there be examples of defining your own + +.. COMMENT: Device Driver Table, Init task table, etc.? + + +Configuring a System +#################### + +.. COMMENT: === Introduction === + +Introduction +============ + +RTEMS must be configured for an application. This configuration +encompasses a variety of information including the length of each clock +tick, the maximum number of each information RTEMS object that can +be created, the application initialization tasks, the task scheduling +algorithm to be used, and the device drivers in the application. + +Although this information is contained in data structures that are used +by RTEMS at system initialization time, the data structures themselves +should only rarely to be generated by hand. RTEMS provides a set of +macros system which provides a simple standard mechanism to automate +the generation of these structures. +.. index:: confdefs.h +.. index:: confdefs.h +.. index:: +.. index:: + +The RTEMS header file ```` is at the core of the +automatic generation of system configuration. It is based on the idea +of setting macros which define configuration parameters of interest to +the application and defaulting or calculating all others. This variety +of macros can automatically produce all of the configuration data +required for an RTEMS application. + +Trivia: ``confdefs`` is shorthand for a *Configuration Defaults*. + +As a general rule, application developers only specify values +for the configuration parameters of interest to them. They define what +resources or features they require. In most cases, when a parameter is +not specified, it defaults to zero (0) instances, a standards compliant +value, or disabled as appropriate. For example, by default there will be +256 task priority levels but this can be lowered by the application. This +number of priority levels is required to be compliant with the RTEID/ORKID +standards upon which the Classic API is based. There are similar cases +where the default is selected to be compliant with with the POSIX standard. + +For each configuration parameter in the configuration tables, the macro +corresponding to that field is discussed. The RTEMS Maintainers +expect that all systems can be easily configured using the```` mechanism and that using this mechanism will +avoid internal RTEMS configuration changes impacting applications. + +.. COMMENT: === Philosophy === + +Default Value Selection Philosophy +================================== + +The user should be aware that the defaults are intentionally set as +low as possible. By default, no application resources are configured. +The ```` file ensures that at least one application +task or thread is configured and that at least one of the initialization +task/thread tables is configured. + +.. COMMENT: === Sizing the RTEMS Workspace === + +Sizing the RTEMS Workspace +========================== + +The RTEMS Workspace is a user-specified block of memory reserved for +use by RTEMS. The application should NOT modify this memory. This area +consists primarily of the RTEMS data structures whose exact size depends +upon the values specified in the Configuration Table. In addition, +task stacks and floating point context areas are dynamically allocated +from the RTEMS Workspace. + +The ```` mechanism calculates the size of the RTEMS +Workspace automatically. It assumes that all tasks are floating point and +that all will be allocated the minimum stack space. This calculation +includes the amount of memory that will be allocated for internal use +by RTEMS. The automatic calculation may underestimate the workspace +size truly needed by the application, in which case one can use the``CONFIGURE_MEMORY_OVERHEAD`` macro to add a value to the estimate. See `Specify Memory Overhead`_ for more details. + +The memory area for the RTEMS Workspace is determined by the BSP. In case the +RTEMS Workspace is too large for the available memory, then a fatal run-time +error occurs and the system terminates. + +The file ```` will calculate the value of the``work_space_size`` parameter of the Configuration Table. There +are many parameters the application developer can specify to +help ```` in its calculations. Correctly +specifying the application requirements via parameters such as``CONFIGURE_EXTRA_TASK_STACKS`` and ``CONFIGURE_MAXIMUM_TASKS`` +is critical for production software. + +For each class of objects, the allocation can operate in one of two ways. +The default way has an ceiling on the maximum number of object instances +which can concurrently exist in the system. Memory for all instances of +that object class is reserved at system initialization. The second +way allocates memory for an initial number of objects and increases the +current allocation by a fixed increment when required. Both ways allocate +space from inside the RTEMS Workspace. + +See `Unlimited Objects`_ for more details about +the second way, which allows for dynamic allocation of objects and +therefore does not provide determinism. This mode is useful mostly for +when the number of objects cannot be determined ahead of time or when +porting software for which you do not know the object requirements. + +The space needed for stacks and for RTEMS objects will vary from +one version of RTEMS and from one target processor to another. +Therefore it is safest to use ```` and specify +your application’s requirements in terms of the numbers of objects and +multiples of ``RTEMS_MINIMUM_STACK_SIZE``, as far as is possible. The +automatic estimates of space required will in general change when: + +- a configuration parameter is changed, + +- task or interrupt stack sizes change, + +- the floating point attribute of a task changes, + +- task floating point attribute is altered, + +- RTEMS is upgraded, or + +- the target processor is changed. + +Failure to provide enough space in the RTEMS Workspace may result in fatal +run-time errors terminating the system. + +.. COMMENT: === Potential Issues === + +Potential Issues with RTEMS Workspace Size Estimation +===================================================== + +The ```` file estimates the amount of memory +required for the RTEMS Workspace. This estimate is only as accurate +as the information given to ```` and may be either +too high or too low for a variety of reasons. Some of the reasons that```` may reserve too much memory for RTEMS are: + +- All tasks/threads are assumed to be floating point. + +Conversely, there are many more reasons that the resource estimate could be +too low: + +- Task/thread stacks greater than minimum size must be + accounted for explicitly by developer. + +- Memory for messages is not included. + +- Device driver requirements are not included. + +- Network stack requirements are not included. + +- Requirements for add-on libraries are not included. + +In general, ```` is very accurate when given enough +information. However, it is quite easy to use a library and forget to +account for its resources. + +.. COMMENT: === Format to be followed for making changes in this file === + +Format to be followed for making changes in this file +===================================================== + +- MACRO NAME + Should be alphanumeric. Can have ’_’ (underscore). + +- DATA TYPE + Please refer to all existing formats. + +- RANGE: + + The range depends on the Data Type of the macro. + + - − If the data type is of type task priority, then its value should + be an integer in the range of 1 to 255. + - − If the data type is an integer, then it can have numbers, characters + (in case the value is defined using another macro) and arithmetic operations + (+, -, \*, /). + - − If the data type is a function pointer the first character + should be an alphabet or an underscore. The rest of the string + can be alphanumeric. + - − If the data type is RTEMS Attributes or RTEMS Mode then + the string should be alphanumeric. + - − If the data type is RTEMS NAME then the value should be + an integer>=0 or RTEMS_BUILD_NAME( ’U’, ’I’, ’1’, ’ ’ ) + +- DEFAULT VALUE + + The default value should be in the following formats- + Please note that the ’.’ (full stop) is necessary. + + - − In case the value is not defined then: + This is not defined by default. + - − If we know the default value then: + The default value is XXX. + - − If the default value is BSP Specific then: + This option is BSP specific. + +- DESCRIPTION + The description of the macro. (No specific format) + +- NOTES + Any further notes. (No specific format) + +.. COMMENT: === Configuration Example === + +Configuration Example +===================== + +In the following example, the configuration information for a system +with a single message queue, four (4) tasks, and a timeslice of +fifty (50) milliseconds is as follows: +.. code:: c + + #include + #define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER + #define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER + #define CONFIGURE_MICROSECONDS_PER_TICK 1000 /* 1 millisecond \*/ + #define CONFIGURE_TICKS_PER_TIMESLICE 50 /* 50 milliseconds \*/ + #define CONFIGURE_RTEMS_INIT_TASKS_TABLE + #define CONFIGURE_MAXIMUM_TASKS 4 + #define CONFIGURE_MAXIMUM_MESSAGE_QUEUES 1 + #define CONFIGURE_MESSAGE_BUFFER_MEMORY \\ + CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE(20, sizeof(struct USER_MESSAGE)) + #define CONFIGURE_INIT + #include + +In this example, only a few configuration parameters are specified. The +impact of these are as follows: + +- The example specified ``CONFIGURE_RTEMS_INIT_TASK_TABLE`` + but did not specify any additional parameters. This results in a + configuration of an application which will begin execution of a single + initialization task named ``Init`` which is non-preemptible and at + priority one (1). + +- By specifying ``CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER``, + this application is configured to have a clock tick device + driver. Without a clock tick device driver, RTEMS has no way to know + that time is passing and will be unable to support delays and wall + time. Further configuration details about time are + provided. Per ``CONFIGURE_MICROSECONDS_PER_TICK`` and``CONFIGURE_TICKS_PER_TIMESLICE``, the user specified they wanted a + clock tick to occur each millisecond, and that the length of a timeslice + would be fifty (50) milliseconds. + +- By specifying ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``, + the application will include a console device driver. Although the + console device driver may support a combination of multiple serial + ports and display and keyboard combinations, it is only required to + provide a single device named ``/dev/console``. This device will + be used for Standard Input, Output and Error I/O Streams. Thus when``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER`` is specified, implicitly + three (3) file descriptors are reserved for the Standard I/O Streams and + those file descriptors are associated with ``/dev/console`` during + initialization. All console devices are expected to support the POSIX*termios* interface. + +- The example above specifies via ``CONFIGURE_MAXIMUM_TASKS`` + that the application requires a maximum of four (4) + simultaneously existing Classic API tasks. Similarly, by specifying``CONFIGURE_MAXIMUM_MESSAGE_QUEUES``, there may be a maximum of only + one (1) concurrently existent Classic API message queues. + +- The most surprising configuration parameter in this example is the + use of ``CONFIGURE_MESSAGE_BUFFER_MEMORY``. Message buffer memory is + allocated from the RTEMS Workspace and must be accounted for. In this + example, the single message queue will have up to twenty (20) messages + of type ``struct USER_MESSAGE``. + +- The ``CONFIGURE_INIT`` constant must be defined in order to + make ```` instantiate the configuration data + structures. This can only be defined in one source file per + application that includes ```` or the symbol + table will be instantiated multiple times and linking errors + produced. + +This example illustrates that parameters have default values. Among +other things, the application implicitly used the following defaults: + +- All unspecified types of communications and synchronization objects + in the Classic and POSIX Threads API have maximums of zero (0). + +- The filesystem will be the default filesystem which is the In-Memory File + System (IMFS). + +- The application will have the default number of priority levels. + +- The minimum task stack size will be that recommended by RTEMS for + the target architecture. + +.. COMMENT: === Unlimited Objects === + + +Unlimited Objects +----------------- + +In real-time embedded systems the RAM is normally a limited, critical +resource and dynamic allocation is avoided as much as possible to +ensure predictable, deterministic execution times. For such cases, see `Sizing the RTEMS Workspace`_ for an overview +of how to tune the size of the workspace. Frequently when users are +porting software to RTEMS the precise resource requirements of the +software is unknown. In these situations users do not need to control +the size of the workspace very tightly because they just want to get +the new software to run; later they can tune the workspace size as needed. + +The following API-independent object classes can be configured in +unlimited mode: + +- POSIX Keys + +- POSIX Key Value Pairs + +The following object classes in the Classic API can be configured in +unlimited mode: + +- Tasks + +- Timers + +- Semaphores + +- Message Queues + +- Periods + +- Barriers + +- Partitions + +- Regions + +- Ports + +Additionally, the following object classes from the POSIX API can be +configured in unlimited mode: + +- Threads + +- Mutexes + +- Condition Variables + +- Timers + +- Message Queues + +- Message Queue Descriptors + +- Semaphores + +- Barriers + +- Read/Write Locks + +- Spinlocks + +The following object classes can *not* be configured in unlimited mode: + +- Drivers + +- File Descriptors + +- User Extensions + +- POSIX Queued Signals + +Due to the memory requirements of unlimited objects it is strongly recommended +to use them only in combination with the unified work areas. See `Separate or Unified Work Areas`_ for more information +on unified work areas. + +The following example demonstrates how the two simple configuration defines for +unlimited objects and unified works areas can replace many seperate +configuration defines for supported object classes: +.. code:: c + + #define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER + #define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER + #define CONFIGURE_UNIFIED_WORK_AREAS + #define CONFIGURE_UNLIMITED_OBJECTS + #define CONFIGURE_RTEMS_INIT_TASKS_TABLE + #define CONFIGURE_INIT + #include + +Users are cautioned that using unlimited objects is not recommended for +production software unless the dynamic growth is absolutely required. It +is generally considered a safer embedded systems programming practice to +know the system limits rather than experience an out of memory error +at an arbitrary and largely unpredictable time in the field. + +.. COMMENT: === Per Object Class Unlimited Object Instances === + +Per Object Class Unlimited Object Instances +------------------------------------------- +.. index:: rtems_resource_unlimited + +When the number of objects is not known ahead of time, RTEMS provides an +auto-extending mode that can be enabled individually for each object +type by using the macro ``rtems_resource_unlimited``. This takes a value +as a parameter, and is used to set the object maximum number field in +an API Configuration table. The value is an allocation unit size. When +RTEMS is required to grow the object table it is grown by this +size. The kernel will return the object memory back to the RTEMS Workspace +when an object is destroyed. The kernel will only return an allocated +block of objects to the RTEMS Workspace if at least half the allocation +size of free objects remain allocated. RTEMS always keeps one +allocation block of objects allocated. Here is an example of using``rtems_resource_unlimited``: +.. code:: c + + #define CONFIGURE_MAXIMUM_TASKS rtems_resource_unlimited(5) + +.. index:: rtems_resource_is_unlimited +.. index:: rtems_resource_maximum_per_allocation + +Object maximum specifications can be evaluated with the``rtems_resource_is_unlimited`` and``rtems_resource_maximum_per_allocation`` macros. + +.. COMMENT: === Unlimited Object Instances === + +Unlimited Object Instances +-------------------------- + +To ease the burden of developers who are porting new software RTEMS +also provides the capability to make all object classes listed above +operate in unlimited mode in a simple manner. The application developer +is only responsible for enabling unlimited objects and specifying the +allocation size. + +.. COMMENT: === CONFIGURE_UNLIMITED_OBJECTS === + +Enable Unlimited Object Instances +--------------------------------- +.. index:: CONFIGURE_UNLIMITED_OBJECTS + +*CONSTANT:* + ``CONFIGURE_UNLIMITED_OBJECTS`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_UNLIMITED_OBJECTS`` enables ``rtems_resource_unlimited`` +mode for Classic API and POSIX API objects that do not already have a +specific maximum limit defined. + +**NOTES:** + +When using unlimited objects, it is common practice to also specify``CONFIGURE_UNIFIED_WORK_AREAS`` so the system operates with a single +pool of memory for both RTEMS and application memory allocations. + +.. COMMENT: === CONFIGURE_UNLIMITED_ALLOCATION_SIZE === + +Specify Unlimited Objects Allocation Size +----------------------------------------- + +*CONSTANT:* + ``CONFIGURE_UNLIMITED_ALLOCATION_SIZE`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + If not defined and ``CONFIGURE_UNLIMITED_OBJECTS`` is defined, the + default value is eight (8). + +**DESCRIPTION:** + +``CONFIGURE_UNLIMITED_ALLOCATION_SIZE`` provides an +allocation size to use for ``rtems_resource_unlimited`` when using``CONFIGURE_UNLIMITED_OBJECTS``. + +**NOTES:** + +By allowing users to declare all resources as being unlimited +the user can avoid identifying and limiting the resources used.``CONFIGURE_UNLIMITED_OBJECTS`` does not support varying the allocation +sizes for different objects; users who want that much control can define +the ``rtems_resource_unlimited`` macros themselves. +.. code:: c + + #define CONFIGURE_UNLIMITED_OBJECTS + #define CONFIGURE_UNLIMITED_ALLOCATION_SIZE 5 + +.. COMMENT: === Classic API Configuration === + +Classic API Configuration +========================= + +This section defines the Classic API related system configuration +parameters supported by ````. + +.. COMMENT: === CONFIGURE_MAXIMUM_TASKS === + +Specify Maximum Classic API Tasks +--------------------------------- +.. index:: CONFIGURE_MAXIMUM_TASKS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_TASKS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_TASKS`` is the maximum number of Classic API +Tasks that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +The calculations for the required memory in the RTEMS Workspace +for tasks assume that each task has a minimum stack size and +has floating point support enabled. The configuration parameter``CONFIGURE_EXTRA_TASK_STACKS`` is used to specify task stack +requirements *ABOVE* the minimum size required. See `Reserve Task/Thread Stack Memory Above Minimum`_ +for more information about ``CONFIGURE_EXTRA_TASK_STACKS``. + +The maximum number of POSIX threads is specified by``CONFIGURE_MAXIMUM_POSIX_THREADS``. + +.. COMMENT: XXX - Add xref to CONFIGURE_MAXIMUM_POSIX_THREADS. + +A future enhancement to ```` could be to eliminate +the assumption that all tasks have floating point enabled. This would +require the addition of a new configuration parameter to specify the +number of tasks which enable floating point support. + +.. COMMENT: === CONFIGURE_MAXIMUM_TIMERS === + +Specify Maximum Classic API Timers +---------------------------------- +.. index:: CONFIGURE_MAXIMUM_TIMERS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_TIMERS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_TIMERS`` is the maximum number of Classic API +Timers that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_SEMAPHORES === + +Specify Maximum Classic API Semaphores +-------------------------------------- +.. index:: CONFIGURE_MAXIMUM_SEMAPHORES + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_SEMAPHORES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_SEMAPHORES`` is the maximum number of Classic +API Semaphores that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_MRSP_SEMAPHORES === + +Specify Maximum Classic API Semaphores usable with MrsP +------------------------------------------------------- +.. index:: CONFIGURE_MAXIMUM_MRSP_SEMAPHORES + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_MRSP_SEMAPHORES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_MRSP_SEMAPHORES`` is the +maximum number of Classic API Semaphores using the Multiprocessor Resource +Sharing Protocol (MrsP) that can be concurrently active. + +**NOTES:** + +This configuration option is only used on SMP configurations. On uni-processor +configurations the Priority Ceiling Protocol is used for MrsP semaphores and +thus no extra memory is necessary. + +.. COMMENT: === CONFIGURE_MAXIMUM_MESSAGE_QUEUES === + +Specify Maximum Classic API Message Queues +------------------------------------------ +.. index:: CONFIGURE_MAXIMUM_MESSAGE_QUEUES + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_MESSAGE_QUEUES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_MESSAGE_QUEUES`` is the maximum number of Classic +API Message Queues that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_BARRIERS === + +Specify Maximum Classic API Barriers +------------------------------------ +.. index:: CONFIGURE_MAXIMUM_BARRIERS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_BARRIERS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_BARRIERS`` is the maximum number of Classic +API Barriers that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_PERIODS === + +Specify Maximum Classic API Periods +----------------------------------- +.. index:: CONFIGURE_MAXIMUM_PERIODS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_PERIODS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_PERIODS`` is the maximum number of Classic +API Periods that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_PARTITIONS === + +Specify Maximum Classic API Partitions +-------------------------------------- +.. index:: CONFIGURE_MAXIMUM_PARTITIONS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_PARTITIONS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_PARTITIONS`` is the maximum number of Classic +API Partitions that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_REGIONS === + +Specify Maximum Classic API Regions +----------------------------------- +.. index:: CONFIGURE_MAXIMUM_REGIONS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_REGIONS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_REGIONS`` is the maximum number of Classic +API Regions that can be concurrently active. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_MAXIMUM_PORTS === + +Specify Maximum Classic API Ports +--------------------------------- +.. index:: CONFIGURE_MAXIMUM_PORTS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_PORTS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_PORTS`` is the maximum number of Classic +API Ports that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_USER_EXTENSIONS === + +Specify Maximum Classic API User Extensions +------------------------------------------- +.. index:: CONFIGURE_MAXIMUM_USER_EXTENSIONS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_USER_EXTENSIONS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_USER_EXTENSIONS`` is the maximum number of Classic +API User Extensions that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === Classic API Initialization Task Configuration === + +Classic API Initialization Tasks Table Configuration +==================================================== + +The ```` configuration system can automatically +generate an Initialization Tasks Table named``Initialization_tasks`` with a single entry. The following +parameters control the generation of that table. + +.. COMMENT: === CONFIGURE_RTEMS_INIT_TASKS_TABLE === + +Instantiate Classic API Initialization Task Table +------------------------------------------------- +.. index:: CONFIGURE_RTEMS_INIT_TASKS_TABLE + +*CONSTANT:* + ``CONFIGURE_RTEMS_INIT_TASKS_TABLE`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_RTEMS_INIT_TASKS_TABLE`` is defined if the user wishes +to use a Classic RTEMS API Initialization Task Table. The table built by```` specifies the parameters for a single task. This +is sufficient for applications which initialization the system from a +single task. + +By default, this field is not defined as the user MUST select their own +API for initialization tasks. + +**NOTES:** + +The application may choose to use the initialization tasks or threads +table from another API. + +A compile time error will be generated if the user does not configure +any initialization tasks or threads. + +.. COMMENT: === CONFIGURE_INIT_TASK_ENTRY_POINT === + +Specifying Classic API Initialization Task Entry Point +------------------------------------------------------ +.. index:: CONFIGURE_INIT_TASK_ENTRY_POINT + +*CONSTANT:* + ``CONFIGURE_INIT_TASK_ENTRY_POINT`` + +*DATA TYPE:* + Task entry function pointer (``rtems_task_entry``). + +*RANGE:* + Valid task entry function pointer. + +*DEFAULT VALUE:* + The default value is ``Init``. + +**DESCRIPTION:** + +``CONFIGURE_INIT_TASK_ENTRY_POINT`` is the entry point (a.k.a. function +name) of the single initialization task defined by the Classic API +Initialization Tasks Table. + +**NOTES:** + +The user must implement the function ``Init`` or the function name provided +in this configuration parameter. + +.. COMMENT: === CONFIGURE_INIT_TASK_NAME === + +Specifying Classic API Initialization Task Name +----------------------------------------------- +.. index:: CONFIGURE_INIT_TASK_NAME + +*CONSTANT:* + ``CONFIGURE_INIT_TASK_NAME`` + +*DATA TYPE:* + RTEMS Name (``rtems_name``). + +*RANGE:* + Any value. + +*DEFAULT VALUE:* + The default value is ``rtems_build_name( 'U', 'I', '1', ' ' )``. + +**DESCRIPTION:** + +``CONFIGURE_INIT_TASK_NAME`` is the name of the single initialization +task defined by the Classic API Initialization Tasks Table. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_INIT_TASK_STACK_SIZE === + +Specifying Classic API Initialization Task Stack Size +----------------------------------------------------- +.. index:: CONFIGURE_INIT_TASK_STACK_SIZE + +*CONSTANT:* + ``CONFIGURE_INIT_TASK_STACK_SIZE`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is RTEMS_MINIMUM_STACK_SIZE. + +**DESCRIPTION:** + +``CONFIGURE_INIT_TASK_STACK_SIZE`` is the stack size of the single +initialization task defined by the Classic API Initialization Tasks Table. + +**NOTES:** + +If the stack size specified is greater than the configured minimum, +it must be accounted for in ``CONFIGURE_EXTRA_TASK_STACKS``. +See `Reserve Task/Thread Stack Memory Above Minimum`_ +for more information about ``CONFIGURE_EXTRA_TASK_STACKS``. + +.. COMMENT: === CONFIGURE_INIT_TASK_PRIORITY === + +Specifying Classic API Initialization Task Priority +--------------------------------------------------- +.. index:: CONFIGURE_INIT_TASK_PRIORITY + +*CONSTANT:* + ``CONFIGURE_INIT_TASK_PRIORITY`` + +*DATA TYPE:* + RTEMS Task Priority (``rtems_task_priority``). + +*RANGE:* + One (1) to CONFIGURE_MAXIMUM_PRIORITY. + +*DEFAULT VALUE:* + The default value is 1, which is the highest priority in the + Classic API. + +**DESCRIPTION:** + +``CONFIGURE_INIT_TASK_PRIORITY`` is the initial priority of the single +initialization task defined by the Classic API Initialization Tasks Table. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_INIT_TASK_ATTRIBUTES === + +Specifying Classic API Initialization Task Attributes +----------------------------------------------------- +.. index:: CONFIGURE_INIT_TASK_ATTRIBUTES + +*CONSTANT:* + ``CONFIGURE_INIT_TASK_ATTRIBUTES`` + +*DATA TYPE:* + RTEMS Attributes (``rtems_attribute``). + +*RANGE:* + Valid task attribute sets. + +*DEFAULT VALUE:* + The default value is ``RTEMS_DEFAULT_ATTRIBUTES``. + +**DESCRIPTION:** + +``CONFIGURE_INIT_TASK_ATTRIBUTES`` is the task attributes of the single +initialization task defined by the Classic API Initialization Tasks Table. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_INIT_TASK_INITIAL_MODES === + +Specifying Classic API Initialization Task Modes +------------------------------------------------ +.. index:: CONFIGURE_INIT_TASK_INITIAL_MODES + +*CONSTANT:* + ``CONFIGURE_INIT_TASK_INITIAL_MODES`` + +*DATA TYPE:* + RTEMS Mode (``rtems_mode``). + +*RANGE:* + Valid task mode sets. + +*DEFAULT VALUE:* + The default value is ``RTEMS_NO_PREEMPT``. + +**DESCRIPTION:** + +``CONFIGURE_INIT_TASK_INITIAL_MODES`` is the initial execution mode of +the single initialization task defined by the Classic API Initialization +Tasks Table. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_INIT_TASK_ARGUMENTS === + +Specifying Classic API Initialization Task Arguments +---------------------------------------------------- +.. index:: CONFIGURE_INIT_TASK_ARGUMENTS + +*CONSTANT:* + ``CONFIGURE_INIT_TASK_ARGUMENTS`` + +*DATA TYPE:* + RTEMS Task Argument (``rtems_task_argument``). + +*RANGE:* + Complete range of the type. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_INIT_TASK_ARGUMENTS`` is the task argument of the single +initialization task defined by the Classic API Initialization Tasks Table. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_HAS_OWN_INIT_TASK_TABLE === + +Not Using Generated Initialization Tasks Table +---------------------------------------------- +.. index:: CONFIGURE_HAS_OWN_INIT_TASK_TABLE + +*CONSTANT:* + ``CONFIGURE_HAS_OWN_INIT_TASK_TABLE`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_HAS_OWN_INIT_TASK_TABLE`` is defined if the user wishes +to define their own Classic API Initialization Tasks Table. This table +should be named ``Initialization_tasks``. + +**NOTES:** + +This is a seldom used configuration parameter. The most likely use case +is when an application desires to have more than one initialization task. + +.. COMMENT: === POSIX API Configuration === + +POSIX API Configuration +======================= + +The parameters in this section are used to configure resources +for the RTEMS POSIX API. They are only relevant if the POSIX API +is enabled at configure time using the ``--enable-posix`` option. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_THREADS === + +Specify Maximum POSIX API Threads +--------------------------------- +.. index:: CONFIGURE_MAXIMUM_POSIX_THREADS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_THREADS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_THREADS`` is the maximum number of POSIX API +Threads that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +This calculations for the required memory in the RTEMS Workspace +for threads assume that each thread has a minimum stack size and +has floating point support enabled. The configuration parameter``CONFIGURE_EXTRA_TASK_STACKS`` is used to specify thread stack +requirements *ABOVE* the minimum size required. +See `Reserve Task/Thread Stack Memory Above Minimum`_ +for more information about ``CONFIGURE_EXTRA_TASK_STACKS``. + +The maximum number of Classic API Tasks is specified by``CONFIGURE_MAXIMUM_TASKS``. + +All POSIX threads have floating point enabled. + +.. COMMENT: XXX - Add xref to CONFIGURE_MAXIMUM_TASKS. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_MUTEXES === + +Specify Maximum POSIX API Mutexes +--------------------------------- +.. index:: CONFIGURE_MAXIMUM_POSIX_MUTEXES + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_MUTEXES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_MUTEXES`` is the maximum number of POSIX +API Mutexes that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES === + +Specify Maximum POSIX API Condition Variables +--------------------------------------------- +.. index:: CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES`` is the maximum number +of POSIX API Condition Variables that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_KEYS === + +Specify Maximum POSIX API Keys +------------------------------ +.. index:: CONFIGURE_MAXIMUM_POSIX_KEYS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_KEYS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_KEYS`` is the maximum number of POSIX +API Keys that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: XXX - Key pairs + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_TIMERS === + +Specify Maximum POSIX API Timers +-------------------------------- +.. index:: CONFIGURE_MAXIMUM_POSIX_TIMERS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_TIMERS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_TIMERS`` is the maximum number of POSIX +API Timers that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS === + +Specify Maximum POSIX API Queued Signals +---------------------------------------- +.. index:: CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS`` is the maximum number of POSIX +API Queued Signals that can be concurrently active. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES === + +Specify Maximum POSIX API Message Queues +---------------------------------------- +.. index:: CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES`` is the maximum number of POSIX +API Message Queues that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: XXX - memory for buffers note + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS === + +Specify Maximum POSIX API Message Queue Descriptors +--------------------------------------------------- +.. index:: CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + greater than or equal to ``CONFIGURE_MAXIMUM_POSIX_MESSAGES_QUEUES`` + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS`` is the maximum +number of POSIX API Message Queue Descriptors that can be concurrently +active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUE_DESCRIPTORS`` should be +greater than or equal to ``CONFIGURE_MAXIMUM_POSIX_MESSAGE_QUEUES``. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_SEMAPHORES === + +Specify Maximum POSIX API Semaphores +------------------------------------ +.. index:: CONFIGURE_MAXIMUM_POSIX_SEMAPHORES + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_SEMAPHORES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_SEMAPHORES`` is the maximum number of POSIX +API Semaphores that can be concurrently active. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_BARRIERS === + +Specify Maximum POSIX API Barriers +---------------------------------- +.. index:: CONFIGURE_MAXIMUM_POSIX_BARRIERS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_BARRIERS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_BARRIERS`` is the maximum number of POSIX +API Barriers that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_SPINLOCKS === + +Specify Maximum POSIX API Spinlocks +----------------------------------- +.. index:: CONFIGURE_MAXIMUM_POSIX_SPINLOCKS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_SPINLOCKS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_SPINLOCKS`` is the maximum number of POSIX +API Spinlocks that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === CONFIGURE_MAXIMUM_POSIX_RWLOCKS === + +Specify Maximum POSIX API Read/Write Locks +------------------------------------------ +.. index:: CONFIGURE_MAXIMUM_POSIX_RWLOCKS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_POSIX_RWLOCKS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_POSIX_RWLOCKS`` is the maximum number of POSIX +API Read/Write Locks that can be concurrently active. + +**NOTES:** + +This object class can be configured in unlimited allocation mode. + +.. COMMENT: === POSIX Initialization Threads Table Configuration === + +POSIX Initialization Threads Table Configuration +================================================ + +The ```` configuration system can automatically +generate a POSIX Initialization Threads Table named``POSIX_Initialization_threads`` with a single entry. The following +parameters control the generation of that table. + +.. COMMENT: === CONFIGURE_POSIX_INIT_THREAD_TABLE === + +Instantiate POSIX API Initialization Thread Table +------------------------------------------------- +.. index:: CONFIGURE_POSIX_INIT_THREAD_TABLE + +*CONSTANT:* + .. index:: CONFIGURE_POSIX_INIT_THREAD_TABLE + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This field is not defined by default, as the user MUST select their own + API for initialization tasks. + +**DESCRIPTION:** + +``CONFIGURE_POSIX_INIT_THREAD_TABLE`` is defined if the user wishes +to use a POSIX API Initialization Threads Table. The table built +by ```` specifies the parameters for a single +thread. This is sufficient for applications which initialization the +system from a +single task. + +By default, this field is not defined as the user MUST select their own +API for initialization tasks. + +**NOTES:** + +The application may choose to use the initialization tasks or threads +table from another API. + +A compile time error will be generated if the user does not configure +any initialization tasks or threads. + +.. COMMENT: === CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT === + +Specifying POSIX API Initialization Thread Entry Point +------------------------------------------------------ +.. index:: CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT + +*CONSTANT:* + ``CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT`` + +*DATA TYPE:* + POSIX thread function pointer (``void \*(*entry_point)(void \*)``). + +*RANGE:* + Undefined or a valid POSIX thread function pointer. + +*DEFAULT VALUE:* + The default value is ``POSIX_Init``. + +**DESCRIPTION:** + +``CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT`` is the entry point +(a.k.a. function name) of the single initialization thread defined by +the POSIX API Initialization Threads Table. + +**NOTES:** + +The user must implement the function ``POSIX_Init`` or the function name +provided in this configuration parameter. + +.. COMMENT: === CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE === + +Specifying POSIX API Initialization Thread Stack Size +----------------------------------------------------- +.. index:: CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE + +*CONSTANT:* + ``CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 2 * RTEMS_MINIMUM_STACK_SIZE. + +**DESCRIPTION:** + +``CONFIGURE_POSIX_INIT_THREAD_STACK_SIZE`` is the stack size of the +single initialization thread defined by the POSIX API Initialization +Threads Table. + +**NOTES:** + +If the stack size specified is greater than the configured minimum, +it must be accounted for in ``CONFIGURE_EXTRA_TASK_STACKS``. +See `Reserve Task/Thread Stack Memory Above Minimum`_ +for more information about ``CONFIGURE_EXTRA_TASK_STACKS``. + +.. COMMENT: === CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE === + +Not Using Generated POSIX Initialization Threads Table +------------------------------------------------------ +.. index:: CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE + +*CONSTANT:* + ``CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE`` is defined if the +user wishes to define their own POSIX API Initialization Threads Table. +This table should be named ``POSIX_Initialization_threads``. + +**NOTES:** + +This is a seldom used configuration parameter. The most likely use case +is when an application desires to have more than one initialization task. + +.. COMMENT: === Basic System Information === + +Basic System Information +======================== + +This section defines the general system configuration parameters supported by````. + +.. COMMENT: === CONFIGURE_UNIFIED_WORK_AREAS === + + +Separate or Unified Work Areas +------------------------------ +.. index:: CONFIGURE_UNIFIED_WORK_AREAS +.. index:: unified work areas +.. index:: separate work areas +.. index:: RTEMS Workspace +.. index:: C Program Heap + +*CONSTANT:* + ``CONFIGURE_UNIFIED_WORK_AREAS`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default, which specifies that the C Program Heap + and the RTEMS Workspace will be separate. + +**DESCRIPTION:** + +When defined, the C Program Heap and the RTEMS Workspace will be one pool +of memory. + +When not defined, there will be separate memory pools for the RTEMS +Workspace and C Program Heap. + +**NOTES:** + +Having separate pools does have some advantages in the event a task blows +a stack or writes outside its memory area. However, in low memory systems +the overhead of the two pools plus the potential for unused memory in +either pool is very undesirable. + +In high memory environments, this is desirable when you want to use the +RTEMS "unlimited" objects option. You will be able to create objects +until you run out of all available memory rather then just until you +run out of RTEMS Workspace. + +.. COMMENT: === CONFIGURE_MICROSECONDS_PER_TICK === + +Length of Each Clock Tick +------------------------- +.. index:: CONFIGURE_MICROSECONDS_PER_TICK +.. index:: tick quantum + +*CONSTANT:* + ``CONFIGURE_MICROSECONDS_PER_TICK`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + This is not defined by default. When not defined, + the clock tick quantum is configured to be 10,000 + microseconds which is ten (10) milliseconds. + +**DESCRIPTION:** + +This constant is used to specify the length of time between clock ticks. + +When the clock tick quantum value is too low, the system will spend so +much time processing clock ticks that it does not have processing time +available to perform application work. In this case, the system will +become unresponsive. + +The lowest practical time quantum varies widely based upon the speed +of the target hardware and the architectural overhead associated with +interrupts. In general terms, you do not want to configure it lower than +is needed for the application. + +The clock tick quantum should be selected such that it all blocking and +delay times in the application are evenly divisible by it. Otherwise, +rounding errors will be introduced which may negatively impact the +application. + +**NOTES:** + +This configuration parameter has no impact if the Clock Tick Device +driver is not configured. + +There may be BSP specific limits on the resolution or maximum value of +a clock tick quantum. + +.. COMMENT: === CONFIGURE_TICKS_PER_TIMESLICE === + +Specifying Timeslicing Quantum +------------------------------ +.. index:: CONFIGURE_TICKS_PER_TIMESLICE +.. index:: ticks per timeslice + +*CONSTANT:* + ``CONFIGURE_TICKS_PER_TIMESLICE`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is 50. + +**DESCRIPTION:** + +This configuration parameter specifies the length of the timeslice +quantum in ticks for each task. + +**NOTES:** + +This configuration parameter has no impact if the Clock Tick Device +driver is not configured. + +.. COMMENT: === CONFIGURE_MAXIMUM_PRIORITY === + +Specifying the Number of Thread Priority Levels +----------------------------------------------- +.. index:: CONFIGURE_MAXIMUM_PRIORITY +.. index:: maximum priority +.. index:: number of priority levels + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_PRIORITY`` + +*DATA TYPE:* + Unsigned integer (``uint8_t``). + +*RANGE:* + Valid values for this configuration parameter must be one (1) less than + than a power of two (2) between 4 and 256 inclusively. In other words, + valid values are 3, 7, 31, 63, 127, and 255. + +*DEFAULT VALUE:* + The default value is 255, because RTEMS must support 256 priority levels to be + compliant with various standards. These priorities range from zero (0) to 255. + +**DESCRIPTION:** + +This configuration parameter specified the maximum numeric priority +of any task in the system and one less that the number of priority levels +in the system. + +Reducing the number of priorities in the system reduces the amount of +memory allocated from the RTEMS Workspace. + +**NOTES:** + +The numerically greatest priority is the logically lowest priority in +the system and will thus be used by the IDLE task. + +Priority zero (0) is reserved for internal use by RTEMS and is not +available to applications. + +With some schedulers, reducing the number of priorities can reduce the +amount of memory used by the scheduler. For example, the Deterministic +Priority Scheduler (DPS) used by default uses three pointers of storage +per priority level. Reducing the number of priorities from 256 levels +to sixteen (16) can reduce memory usage by about three (3) kilobytes. + +.. COMMENT: === CONFIGURE_MINIMUM_TASK_STACK_SIZE === + +Specifying the Minimum Task Size +-------------------------------- +.. index:: CONFIGURE_MINIMUM_TASK_STACK_SIZE +.. index:: minimum task stack size + +*CONSTANT:* + ``CONFIGURE_MINIMUM_TASK_STACK_SIZE`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + This is not defined by default, which sets the executive to the recommended + minimum stack size for this processor. + +**DESCRIPTION:** + +The configuration parameter is set to the number of bytes the application +wants the minimum stack size to be for every task or thread in the system. + +Adjusting this parameter should be done with caution. Examining the actual +usage using the Stack Checker Usage Reporting facility is recommended. + +**NOTES:** + +This parameter can be used to lower the minimum from that +recommended. This can be used in low memory systems to reduce memory +consumption for stacks. However, this must be done with caution as it +could increase the possibility of a blown task stack. + +This parameter can be used to increase the minimum from that +recommended. This can be used in higher memory systems to reduce the +risk of stack overflow without performing analysis on actual consumption. + +.. COMMENT: === CONFIGURE_INTERRUPT_STACK_SIZE === + +Configuring the Size of the Interrupt Stack +------------------------------------------- +.. index:: CONFIGURE_INTERRUPT_STACK_SIZE +.. index:: interrupt stack size + +*CONSTANT:* + ``CONFIGURE_INTERRUPT_STACK_SIZE`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is CONFIGURE_MINIMUM_TASK_STACK_SIZE, which is the minimum + interrupt stack size. + +**DESCRIPTION:** + +``CONFIGURE_INTERRUPT_STACK_SIZE`` is set to the size of the +interrupt stack. The interrupt stack size is often set by the BSP but +since this memory may be allocated from the RTEMS Workspace, it must be +accounted for. + +**NOTES:** + +In some BSPs, changing this constant does NOT change the +size of the interrupt stack, only the amount of memory +reserved for it. + +Patches which result in this constant only being used in memory +calculations when the interrupt stack is intended to be allocated +from the RTEMS Workspace would be welcomed by the RTEMS Project. + +.. COMMENT: === CONFIGURE_EXTRA_TASK_STACKS === + + +Reserve Task/Thread Stack Memory Above Minimum +---------------------------------------------- +.. index:: CONFIGURE_EXTRA_TASK_STACKS +.. index:: memory for task tasks + +*CONSTANT:* + ``CONFIGURE_EXTRA_TASK_STACKS`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Undefined or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +This configuration parameter is set to the number of bytes the +applications wishes to add to the task stack requirements calculated +by ````. + +**NOTES:** + +This parameter is very important. If the application creates tasks with +stacks larger then the minimum, then that memory is NOT accounted for +by ````. + +.. COMMENT: === CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY === + +Automatically Zeroing the RTEMS Workspace and C Program Heap +------------------------------------------------------------ +.. index:: CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY +.. index:: clear C Program Heap +.. index:: clear RTEMS Workspace +.. index:: zero C Program Heap +.. index:: zero RTEMS Workspace + +*CONSTANT:* + ``CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default, unless overridden by the BSP. + The default is *NOT* to zero out the RTEMS Workspace or C Program Heap. + +**DESCRIPTION:** + +This macro indicates whether RTEMS should zero the RTEMS Workspace and +C Program Heap as part of its initialization. If defined, the memory +regions are zeroed. Otherwise, they are not. + +**NOTES:** + +Zeroing memory can add significantly to system boot time. It is not +necessary for RTEMS but is often assumed by support libraries. + +.. COMMENT: === CONFIGURE_STACK_CHECKER_ENABLED === + +Enable The Task Stack Usage Checker +----------------------------------- +.. index:: CONFIGURE_STACK_CHECKER_ENABLED + +*CONSTANT:* + ``CONFIGURE_STACK_CHECKER_ENABLED`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default, and thus stack checking is disabled. + +**DESCRIPTION:** + +This configuration parameter is defined when the application wishes to +enable run-time stack bounds checking. + +**NOTES:** + +In 4.9 and older, this configuration parameter was named``STACK_CHECKER_ON``. + +This increases the time required to create tasks as well as adding +overhead to each context switch. + +.. COMMENT: === CONFIGURE_INITIAL_EXTENSIONS === + +Specify Application Specific User Extensions +-------------------------------------------- +.. index:: CONFIGURE_INITIAL_EXTENSIONS + +*CONSTANT:* + ``CONFIGURE_INITIAL_EXTENSIONS`` + +*DATA TYPE:* + List of user extension initializers (``rtems_extensions_table``). + +*RANGE:* + Undefined or a list of one or more user extensions. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +If ``CONFIGURE_INITIAL_EXTENSIONS`` is defined by the application, +then this application specific set of initial extensions will be placed +in the initial extension table. + +**NOTES:** + +None. + +.. COMMENT: === Custom Stack Allocator === + +Configuring Custom Task Stack Allocation +======================================== + +RTEMS allows the application or BSP to define its own allocation and +deallocation methods for task stacks. This can be used to place task +stacks in special areas of memory or to utilize a Memory Management Unit +so that stack overflows are detected in hardware. + +.. COMMENT: === CONFIGURE_TASK_STACK_ALLOCATOR_INIT === + +Custom Task Stack Allocator Initialization +------------------------------------------ +.. index:: CONFIGURE_TASK_STACK_ALLOCATOR_INIT + +*CONSTANT:* + ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT`` + +*DATA TYPE:* + Function pointer. + +*RANGE:* + Undefined, NULL or valid function pointer. + +*DEFAULT VALUE:* + The default value is NULL, which indicates that + task stacks will be allocated from the RTEMS Workspace. + +**DESCRIPTION:** + +``CONFIGURE_TASK_STACK_ALLOCATOR_INIT`` configures the initialization +method for an application or BSP specific task stack allocation +implementation. + +**NOTES:** + +A correctly configured system must configure the following to be consistent: + +- ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT`` + +- ``CONFIGURE_TASK_STACK_ALLOCATOR`` + +- ``CONFIGURE_TASK_STACK_DEALLOCATOR`` + +.. COMMENT: === CONFIGURE_TASK_STACK_ALLOCATOR === + +Custom Task Stack Allocator +--------------------------- +.. index:: CONFIGURE_TASK_STACK_ALLOCATOR + +.. index:: task stack allocator + +*CONSTANT:* + ``CONFIGURE_TASK_STACK_ALLOCATOR`` + +*DATA TYPE:* + Function pointer. + +*RANGE:* + Undefined or valid function pointer. + +*DEFAULT VALUE:* + The default value is ``_Workspace_Allocate``, which indicates + that task stacks will be allocated from the RTEMS Workspace. + +**DESCRIPTION:** + +``CONFIGURE_TASK_STACK_ALLOCATOR`` may point to a user provided +routine to allocate task stacks. + +**NOTES:** + +A correctly configured system must configure the following to be consistent: + +- ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT`` + +- ``CONFIGURE_TASK_STACK_ALLOCATOR`` + +- ``CONFIGURE_TASK_STACK_DEALLOCATOR`` + +.. COMMENT: === CONFIGURE_TASK_STACK_DEALLOCATOR === + +Custom Task Stack Deallocator +----------------------------- +.. index:: CONFIGURE_TASK_STACK_DEALLOCATOR +.. index:: task stack deallocator + +*CONSTANT:* + ``CONFIGURE_TASK_STACK_DEALLOCATOR`` + +*DATA TYPE:* + Function pointer. + +*RANGE:* + Undefined or valid function pointer. + +*DEFAULT VALUE:* + The default value is ``_Workspace_Free``, which indicates that + task stacks will be allocated from the RTEMS Workspace. + +**DESCRIPTION:** + +``CONFIGURE_TASK_STACK_DEALLOCATOR`` may point to a user provided +routine to free task stacks. + +**NOTES:** + +A correctly configured system must configure the following to be consistent: + +- ``CONFIGURE_TASK_STACK_ALLOCATOR_INIT`` + +- ``CONFIGURE_TASK_STACK_ALLOCATOR`` + +- ``CONFIGURE_TASK_STACK_DEALLOCATOR`` + +.. COMMENT: === Classic API Message Buffers === + +Configuring Memory for Classic API Message Buffers +================================================== + +This section describes the configuration parameters related to specifying +the amount of memory reserved for Classic API Message Buffers. + +.. COMMENT: === CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE === + +Calculate Memory for a Single Classic Message API Message Queue +--------------------------------------------------------------- +.. index:: CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE +.. index:: memory for a single message queue’s buffers + +*CONSTANT:* + ``CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE(max_messages, size_per)`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is None. + +**DESCRIPTION:** + +This is a helper macro which is used to assist in computing the total +amount of memory required for message buffers. Each message queue will +have its own configuration with maximum message size and maximum number +of pending messages. + +The interface for this macro is as follows: +.. code:: c + + CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE(max_messages, size_per) + +Where ``max_messages`` is the maximum number of pending messages +and ``size_per`` is the size in bytes of the user message. + +**NOTES:** + +This macro is only used in support of ``CONFIGURE_MESSAGE_BUFFER_MEMORY``. + +.. COMMENT: === CONFIGURE_MESSAGE_BUFFER_MEMORY === + +Reserve Memory for All Classic Message API Message Queues +--------------------------------------------------------- +.. index:: CONFIGURE_MESSAGE_BUFFER_MEMORY +.. index:: configure message queue buffer memory + +*CONSTANT:* + ``CONFIGURE_MESSAGE_BUFFER_MEMORY`` + +*DATA TYPE:* + integer summation macro + +*RANGE:* + undefined (zero) or calculation resulting in a positive integer + +*DEFAULT VALUE:* + This is not defined by default, and zero (0) memory is reserved. + +**DESCRIPTION:** + +This macro is set to the number of bytes the application requires to be +reserved for pending Classic API Message Queue buffers. + +**NOTES:** + +The following illustrates how the help macro``CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE`` can be used to assist in +calculating the message buffer memory required. In this example, there +are two message queues used in this application. The first message +queue has maximum of 24 pending messages with the message structure +defined by the type ``one_message_type``. The other message queue +has maximum of 500 pending messages with the message structure defined +by the type ``other_message_type``. +.. code:: c + + #define CONFIGURE_MESSAGE_BUFFER_MEMORY \\ + (CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE( \\ + 24, sizeof(one_message_type) + \\ + CONFIGURE_MESSAGE_BUFFERS_FOR_QUEUE( \\ + 500, sizeof(other_message_type) \\ + ) + +.. COMMENT: === Seldom Used Configuration Parameters === + +Seldom Used Configuration Parameters +==================================== + +This section describes configuration parameters supported by```` which are seldom used by applications. These +parameters tend to be oriented to debugging system configurations +and providing work-arounds when the memory estimated by```` is incorrect. + +.. COMMENT: === CONFIGURE_MEMORY_OVERHEAD === + + +Specify Memory Overhead +----------------------- +.. index:: CONFIGURE_MEMORY_OVERHEAD + +*CONSTANT:* + ``CONFIGURE_MEMORY_OVERHEAD`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +Thie parameter is set to the number of kilobytes the application wishes +to add to the requirements calculated by ````. + +**NOTES:** + +This configuration parameter should only be used when it is suspected that +a bug in ```` has resulted in an underestimation. +Typically the memory allocation will be too low when an application does +not account for all message queue buffers or task stacks. + +.. COMMENT: === CONFIGURE_HAS_OWN_CONFIGURATION_TABLE === + +Do Not Generate Configuration Information +----------------------------------------- +.. index:: CONFIGURE_HAS_OWN_CONFIGURATION_TABLE + +*CONSTANT:* + ``CONFIGURE_HAS_OWN_CONFIGURATION_TABLE`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +This configuration parameter should only be defined if the application +is providing their own complete set of configuration tables. + +**NOTES:** + +None. + +.. COMMENT: === C Library Support Configuration === + +C Library Support Configuration +=============================== + +This section defines the file system and IO library +related configuration parameters supported by````. + +.. COMMENT: === CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS === + +Specify Maximum Number of File Descriptors +------------------------------------------ +.. index:: CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS +.. index:: maximum file descriptors + +*CONSTANT:* + ``CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + If ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER`` is defined, then the + default value is 3, otherwise the default value is 0. + Three file descriptors allows RTEMS to support standard input, output, and + error I/O streams on ``/dev/console``. + +**DESCRIPTION:** + +This configuration parameter is set to the maximum number of file like objects +that can be concurrently open. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_TERMIOS_DISABLED === + +Disable POSIX Termios Support +----------------------------- +.. index:: CONFIGURE_TERMIOS_DISABLED + +*CONSTANT:* + ``CONFIGURE_TERMIOS_DISABLED`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default, and resources are reserved for the + termios functionality. + +**DESCRIPTION:** + +This configuration parameter is defined if the software implementing +POSIX termios functionality is not going to be used by this application. + +**NOTES:** + +The termios support library should not be included in an application +executable unless it is directly referenced by the application or a +device driver. + +.. COMMENT: === CONFIGURE_NUMBER_OF_TERMIOS_PORTS === + +Specify Maximum Termios Ports +----------------------------- +.. index:: CONFIGURE_NUMBER_OF_TERMIOS_PORTS + +*CONSTANT:* + ``CONFIGURE_NUMBER_OF_TERMIOS_PORTS`` + +*DATA TYPE:* + Unsigned integer. + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 1, so a console port can be used. + +**DESCRIPTION:** + +This configuration parameter is set to the number of ports using the +termios functionality. Each concurrently active termios port requires +resources. + +**NOTES:** + +If the application will be using serial ports +including, but not limited to, the Console Device +(e.g. ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER``), then it is +highly likely that this configuration parameter should NOT be is defined. + +.. COMMENT: === File System Configuration Parameters === + +File System Configuration Parameters +==================================== + +This section defines File System related configuration parameters. + +.. COMMENT: === CONFIGURE_HAS_OWN_MOUNT_TABLE === + +Providing Application Specific Mount Table +------------------------------------------ +.. index:: CONFIGURE_HAS_OWN_MOUNT_TABLE + +*CONSTANT:* + ``CONFIGURE_HAS_OWN_MOUNT_TABLE`` + +*DATA TYPE:* + Undefined or an array of type ``rtems_filesystem_mount_table_t``. + +*RANGE:* + Undefined or an array of type ``rtems_filesystem_mount_table_t``. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +This configuration parameter is defined when the application +provides their own filesystem mount table. The mount table is an +array of ``rtems_filesystem_mount_table_t`` entries pointed +to by the global variable ``rtems_filesystem_mount_table``. +The number of entries in this table is in an integer variable named``rtems_filesystem_mount_table_t``. + +.. COMMENT: XXX - is the variable name for the count right? + +**NOTES:** + +None. + +.. COMMENT: XXX - Please provide an example + +.. COMMENT: === CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM === + +Configure devFS as Root File System +----------------------------------- +.. index:: CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM + +*CONSTANT:* + ``CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. If no other root file system + configuration parameters are specified, the IMFS will be used as the + root file system. + +**DESCRIPTION:** + +This configuration parameter is defined if the application wishes to +use the device-only filesytem as the root file system. + +**NOTES:** + +The device-only filesystem supports only device nodes and is smaller in +executable code size than the full IMFS and miniIMFS. + +The devFS is comparable in functionality to the pseudo-filesystem name +space provided before RTEMS release 4.5.0. + +.. COMMENT: === CONFIGURE_MAXIMUM_DEVICES === + +Specifying Maximum Devices for devFS +------------------------------------ +.. index:: CONFIGURE_MAXIMUM_DEVICES + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_DEVICES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + If ``BSP_MAXIMUM_DEVICES`` is defined, then the + default value is ``BSP_MAXIMUM_DEVICES``, otherwise the default value is 4. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_DEVICES`` is defined to the number of +individual devices that may be registered in the device file system (devFS). + +**NOTES:** + +This option is specific to the device file system (devFS) and should not be +confused with the ``CONFIGURE_MAXIMUM_DRIVERS`` option. This parameter only +impacts the devFS and thus is only used by ```` when``CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM`` is specified. + +.. COMMENT: === CONFIGURE_APPLICATION_DISABLE_FILESYSTEM === + +Disable File System Support +--------------------------- +.. index:: CONFIGURE_APPLICATION_DISABLE_FILESYSTEM + +*CONSTANT:* + ``CONFIGURE_APPLICATION_DISABLE_FILESYSTEM`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. If no other root file system + configuration parameters are specified, the IMFS will be used as the + root file system. + +**DESCRIPTION:** + +This configuration parameter is defined if the application dose not +intend to use any kind of filesystem support. This include the device +infrastructure necessary to support ``printf()``. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM === + +Use a Root IMFS with a Minimalistic Feature Set +----------------------------------------------- +.. index:: CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM + +*CONSTANT:* + ``CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the following configuration +options will be defined as well + +- ``CONFIGURE_IMFS_DISABLE_CHMOD``, + +- ``CONFIGURE_IMFS_DISABLE_CHOWN``, + +- ``CONFIGURE_IMFS_DISABLE_UTIME``, + +- ``CONFIGURE_IMFS_DISABLE_LINK``, + +- ``CONFIGURE_IMFS_DISABLE_SYMLINK``, + +- ``CONFIGURE_IMFS_DISABLE_READLINK``, + +- ``CONFIGURE_IMFS_DISABLE_RENAME``, and + +- ``CONFIGURE_IMFS_DISABLE_UNMOUNT``. + +.. COMMENT: === CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK === + +Specify Block Size for IMFS +--------------------------- +.. index:: CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK + +*CONSTANT:* + ``CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Valid values for this configuration parameter are a power of two (2) + between 16 and 512 inclusive. In other words, valid values are 16, + 32, 64, 128, 256,and 512. + +*DEFAULT VALUE:* + The default IMFS block size is 128 bytes. + +**DESCRIPTION:** + +This configuration parameter specifies the block size for in-memory files +managed by the IMFS. The configured block size has two impacts. The first +is the average amount of unused memory in the last block of each file. For +example, when the block size is 512, on average one-half of the last block +of each file will remain unused and the memory is wasted. In contrast, +when the block size is 16, the average unused memory per file is only +8 bytes. However, it requires more allocations for the same size file +and thus more overhead per block for the dynamic memory management. + +Second, the block size has an impact on the maximum size file that can +be stored in the IMFS. With smaller block size, the maximum file size +is correspondingly smaller. The following shows the maximum file size +possible based on the configured block size: + +- when the block size is 16 bytes, the maximum file size is 1,328 + bytes. + +- when the block size is 32 bytes, the maximum file size is 18,656 + bytes. + +- when the block size is 64 bytes, the maximum file size is 279,488 + bytes. + +- when the block size is 128 bytes, the maximum file size is + 4,329,344 bytes. + +- when the block size is 256 bytes, the maximum file size is + 68,173,568 bytes. + +- when the block size is 512 bytes, the maximum file size is + 1,082,195,456 bytes. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_CHOWN === + +Disable Change Owner Support of Root IMFS +----------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_CHOWN + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_CHOWN`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to change the +owner is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_CHMOD === + +Disable Change Mode Support of Root IMFS +---------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_CHMOD + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_CHMOD`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to change the +mode is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_UTIME === + +Disable Change Times Support of Root IMFS +----------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_UTIME + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_UTIME`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to change times +is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_LINK === + +Disable Create Hard Link Support of Root IMFS +--------------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_LINK + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_LINK`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to create hard +links is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_SYMLINK === + +Disable Create Symbolic Link Support of Root IMFS +------------------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_SYMLINK + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_SYMLINK`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to create +symbolic links is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_READLINK === + +Disable Read Symbolic Link Support of Root IMFS +----------------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_READLINK + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_READLINK`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to read symbolic +links is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_RENAME === + +Disable Rename Support of Root IMFS +----------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_RENAME + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_RENAME`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to rename nodes +is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_READDIR === + +Disable Directory Read Support of Root IMFS +------------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_READDIR + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_READDIR`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to read a +directory is disabled in the root IMFS. It is still possible to open nodes in +a directory. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_MOUNT === + +Disable Mount Support of Root IMFS +---------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_MOUNT + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_MOUNT`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to mount other +file systems is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_UNMOUNT === + +Disable Unmount Support of Root IMFS +------------------------------------ +.. index:: CONFIGURE_IMFS_DISABLE_UNMOUNT + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_UNMOUNT`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to unmount file +systems is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_MKNOD === + +Disable Make Nodes Support of Root IMFS +--------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_MKNOD + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_MKNOD`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to make +directories, devices, regular files and FIFOs is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_MKNOD_FILE === + +Disable Make Files Support of Root IMFS +--------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_MKNOD_FILE + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_MKNOD_FILE`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to make regular +files is disabled in the root IMFS. + +.. COMMENT: === CONFIGURE_IMFS_DISABLE_RMNOD === + +Disable Remove Nodes Support of Root IMFS +----------------------------------------- +.. index:: CONFIGURE_IMFS_DISABLE_RMNOD + +*CONSTANT:* + ``CONFIGURE_IMFS_DISABLE_RMNOD`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +In case this configuration option is defined, then the support to remove nodes +is disabled in the root IMFS. + +.. COMMENT: === Block Device Cache Configuration === + +Block Device Cache Configuration +================================ + +This section defines Block Device Cache (bdbuf) related configuration +parameters. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_LIBBLOCK === + +Enable Block Device Cache +------------------------- +.. index:: CONFIGURE_APPLICATION_NEEDS_LIBBLOCK + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_LIBBLOCK`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +Provides a Block Device Cache configuration. + +**NOTES:** + +Each option of the Block Device Cache configuration can be explicitly set by +the user with the configuration options below. The Block Device Cache is used +for example by the RFS and DOSFS file systems. + +.. COMMENT: === CONFIGURE_BDBUF_CACHE_MEMORY_SIZE === + +Size of the Cache Memory +------------------------ +.. index:: CONFIGURE_BDBUF_CACHE_MEMORY_SIZE + +*CONSTANT:* + ``CONFIGURE_BDBUF_CACHE_MEMORY_SIZE`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is 32768 bytes. + +**DESCRIPTION:** + +Size of the cache memory in bytes. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_BDBUF_BUFFER_MIN_SIZE === + +Minimum Size of a Buffer +------------------------ +.. index:: CONFIGURE_BDBUF_BUFFER_MIN_SIZE + +*CONSTANT:* + ``CONFIGURE_BDBUF_BUFFER_MIN_SIZE`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is 512 bytes. + +**DESCRIPTION:** + +Defines the minimum size of a buffer in bytes. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_BDBUF_BUFFER_MAX_SIZE === + +Maximum Size of a Buffer +------------------------ +.. index:: CONFIGURE_BDBUF_BUFFER_MAX_SIZE + +*CONSTANT:* + ``CONFIGURE_BDBUF_BUFFER_MAX_SIZE`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + It must be positive and an integral multiple of the buffer minimum size. + +*DEFAULT VALUE:* + The default value is 4096 bytes. + +**DESCRIPTION:** + +Defines the maximum size of a buffer in bytes. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_SWAPOUT_SWAP_PERIOD === + +Swapout Task Swap Period +------------------------ +.. index:: CONFIGURE_SWAPOUT_SWAP_PERIOD + +*CONSTANT:* + ``CONFIGURE_SWAPOUT_SWAP_PERIOD`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is 250 milliseconds. + +**DESCRIPTION:** + +Defines the swapout task swap period in milliseconds. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_SWAPOUT_BLOCK_HOLD === + +Swapout Task Maximum Block Hold Time +------------------------------------ +.. index:: CONFIGURE_SWAPOUT_BLOCK_HOLD + +*CONSTANT:* + ``CONFIGURE_SWAPOUT_BLOCK_HOLD`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is 1000 milliseconds. + +**DESCRIPTION:** + +Defines the swapout task maximum block hold time in milliseconds. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_SWAPOUT_TASK_PRIORITY === + +Swapout Task Priority +--------------------- +.. index:: CONFIGURE_SWAPOUT_TASK_PRIORITY + +*CONSTANT:* + ``CONFIGURE_SWAPOUT_TASK_PRIORITY`` + +*DATA TYPE:* + Task priority (``rtems_task_priority``). + +*RANGE:* + Valid task priority. + +*DEFAULT VALUE:* + The default value is 15. + +**DESCRIPTION:** + +Defines the swapout task priority. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS === + +Maximum Blocks per Read-Ahead Request +------------------------------------- +.. index:: CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS + +*CONSTANT:* + ``CONFIGURE_BDBUF_MAX_READ_AHEAD_BLOCKS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +Defines the maximum blocks per read-ahead request. + +**NOTES:** + +A value of 0 disables the read-ahead task (default). The read-ahead task will +issue speculative read transfers if a sequential access pattern is detected. +This can improve the performance on some systems. + +.. COMMENT: === CONFIGURE_BDBUF_MAX_WRITE_BLOCKS === + +Maximum Blocks per Write Request +-------------------------------- +.. index:: CONFIGURE_BDBUF_MAX_WRITE_BLOCKS + +*CONSTANT:* + ``CONFIGURE_BDBUF_MAX_WRITE_BLOCKS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is 16. + +**DESCRIPTION:** + +Defines the maximum blocks per write request. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_BDBUF_TASK_STACK_SIZE === + +Task Stack Size of the Block Device Cache Tasks +----------------------------------------------- +.. index:: CONFIGURE_BDBUF_TASK_STACK_SIZE + +*CONSTANT:* + ``CONFIGURE_BDBUF_TASK_STACK_SIZE`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is RTEMS_MINIMUM_STACK_SIZE. + +**DESCRIPTION:** + +Defines the task stack size of the Block Device Cache tasks in bytes. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY === + +Read-Ahead Task Priority +------------------------ +.. index:: CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY + +*CONSTANT:* + ``CONFIGURE_BDBUF_READ_AHEAD_TASK_PRIORITY`` + +*DATA TYPE:* + Task priority (``rtems_task_priority``). + +*RANGE:* + Valid task priority. + +*DEFAULT VALUE:* + The default value is 15. + +**DESCRIPTION:** + +Defines the read-ahead task priority. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_SWAPOUT_WORKER_TASKS === + +Swapout Worker Task Count +------------------------- +.. index:: CONFIGURE_SWAPOUT_WORKER_TASKS + +*CONSTANT:* + ``CONFIGURE_SWAPOUT_WORKER_TASKS`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +Defines the swapout worker task count. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY === + +Swapout Worker Task Priority +---------------------------- +.. index:: CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY + +*CONSTANT:* + ``CONFIGURE_SWAPOUT_WORKER_TASK_PRIORITY`` + +*DATA TYPE:* + Task priority (``rtems_task_priority``). + +*RANGE:* + Valid task priority. + +*DEFAULT VALUE:* + The default value is 15. + +**DESCRIPTION:** + +Defines the swapout worker task priority. + +**NOTES:** + +None. + +.. COMMENT: === BSP Specific Settings === + +BSP Specific Settings +===================== + +This section describes BSP specific configuration settings used by````. The BSP specific configuration settings are +defined in ````. + +.. COMMENT: === Disable BSP Settings === + +Disable BSP Configuration Settings +---------------------------------- +.. index:: CONFIGURE_DISABLE_BSP_SETTINGS + +*CONSTANT:* + ``CONFIGURE_DISABLE_BSP_SETTINGS`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +All BSP specific configuration settings can be disabled by the application +with the ``CONFIGURE_DISABLE_BSP_SETTINGS`` option. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK === + +Specify BSP Supports sbrk() +--------------------------- +.. index:: CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK + +*CONSTANT:* + ``CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This option is BSP specific. + +**DESCRIPTION:** + +This configuration parameter is defined by a BSP to indicate that it +does not allocate all available memory to the C Program Heap used by +the Malloc Family of routines. + +If defined, when ``malloc()`` is unable to allocate memory, it will +call the BSP supplied ``sbrk()`` to obtain more memory. + +**NOTES:** + +This parameter should not be defined by the application. Only the BSP +knows how it allocates memory to the C Program Heap. + +.. COMMENT: === BSP_IDLE_TASK_BODY === + +Specify BSP Specific Idle Task +------------------------------ +.. index:: BSP_IDLE_TASK_BODY + +*CONSTANT:* + ``BSP_IDLE_TASK_BODY`` + +*DATA TYPE:* + Function pointer. + +*RANGE:* + Undefined or valid function pointer. + +*DEFAULT VALUE:* + This option is BSP specific. + +**DESCRIPTION:** + +If ``BSP_IDLE_TASK_BODY`` is defined by the BSP and``CONFIGURE_IDLE_TASK_BODY`` is not defined by the application, +then this BSP specific idle task body will be used. + +**NOTES:** + +As it has knowledge of the specific CPU model, system controller logic, +and peripheral buses, a BSP specific IDLE task may be capable of turning +components off to save power during extended periods of no task activity + +.. COMMENT: === BSP_IDLE_TASK_STACK_SIZE === + +Specify BSP Suggested Value for IDLE Task Stack Size +---------------------------------------------------- +.. index:: BSP_IDLE_TASK_STACK_SIZE + +*CONSTANT:* + ``BSP_IDLE_TASK_STACK_SIZE`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Undefined or positive. + +*DEFAULT VALUE:* + This option is BSP specific. + +**DESCRIPTION:** + +If ``BSP_IDLE_TASK_STACK_SIZE`` is defined by the BSP and``CONFIGURE_IDLE_TASK_STACK_SIZE`` is not defined by the application, +then this BSP suggested idle task stack size will be used. + +**NOTES:** + +The order of precedence for configuring the IDLE task stack size is: + +- RTEMS default minimum stack size. + +- If defined, then ``CONFIGURE_MINIMUM_TASK_STACK_SIZE``. + +- If defined, then the BSP specific ``BSP_IDLE_TASK_SIZE``. + +- If defined, then the application specified``CONFIGURE_IDLE_TASK_SIZE``. + +.. COMMENT: XXX - add cross references to other related values. + +.. COMMENT: === BSP_INITIAL_EXTENSION === + +Specify BSP Specific User Extensions +------------------------------------ +.. index:: BSP_INITIAL_EXTENSION + +*CONSTANT:* + ``BSP_INITIAL_EXTENSION`` + +*DATA TYPE:* + List of user extension initializers (``rtems_extensions_table``). + +*RANGE:* + Undefined or a list of user extension initializers. + +*DEFAULT VALUE:* + This option is BSP specific. + +**DESCRIPTION:** + +If ``BSP_INITIAL_EXTENSION`` is defined by the BSP, then this BSP +specific initial extension will be placed as the last entry in the initial +extension table. + +**NOTES:** + +None. + +.. COMMENT: === BSP_INTERRUPT_STACK_SIZE === + +Specifying BSP Specific Interrupt Stack Size +-------------------------------------------- +.. index:: BSP_INTERRUPT_STACK_SIZE + +*CONSTANT:* + ``BSP_INTERRUPT_STACK_SIZE`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Undefined or positive. + +*DEFAULT VALUE:* + This option is BSP specific. + +**DESCRIPTION:** + +If ``BSP_INTERRUPT_STACK_SIZE`` is defined by the BSP and``CONFIGURE_INTERRUPT_STACK_SIZE`` is not defined by the application, +then this BSP specific interrupt stack size will be used. + +**NOTES:** + +None. + +.. COMMENT: === BSP_MAXIMUM_DEVICES === + +Specifying BSP Specific Maximum Devices +--------------------------------------- +.. index:: BSP_MAXIMUM_DEVICES + +*CONSTANT:* + ``BSP_MAXIMUM_DEVICES`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Undefined or positive. + +*DEFAULT VALUE:* + This option is BSP specific. + +**DESCRIPTION:** + +If ``BSP_MAXIMUM_DEVICES`` is defined by the BSP and``CONFIGURE_MAXIMUM_DEVICES`` is not defined by the application, +then this BSP specific maximum device count will be used. + +**NOTES:** + +This option is specific to the device file system (devFS) and should not be +confused with the ``CONFIGURE_MAXIMUM_DRIVERS`` option. This parameter only +impacts the devFS and thus is only used by ```` when``CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM`` is specified. + +.. COMMENT: === BSP_ZERO_WORKSPACE_AUTOMATICALLY === + +BSP Recommends RTEMS Workspace be Cleared +----------------------------------------- +.. index:: BSP_ZERO_WORKSPACE_AUTOMATICALLY + +*CONSTANT:* + ``BSP_ZERO_WORKSPACE_AUTOMATICALLY`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This option is BSP specific. + +**DESCRIPTION:** + +If ``BSP_ZERO_WORKSPACE_AUTOMATICALLY`` is defined by the BSP and``CONFIGURE_ZERO_WORKSPACE_AUTOMATICALLY`` is not defined by the +application, then the workspace will be zeroed automatically. + +**NOTES:** + +Zeroing memory can add significantly to system boot time. It is not +necessary for RTEMS but is often assumed by support libraries. + +.. COMMENT: === CONFIGURE_BSP_PREREQUISITE_DRIVERS === + +Specify BSP Prerequisite Drivers +-------------------------------- +.. index:: CONFIGURE_BSP_PREREQUISITE_DRIVERS + +*CONSTANT:* + ``CONFIGURE_BSP_PREREQUISITE_DRIVERS`` + +*DATA TYPE:* + List of device driver initializers (``rtems_driver_address_table``). + +*RANGE:* + Undefined or array of device drivers. + +*DEFAULT VALUE:* + This option is BSP specific. + +**DESCRIPTION:** + +``CONFIGURE_BSP_PREREQUISITE_DRIVERS`` is defined if the BSP has device +drivers it needs to include in the Device Driver Table. This should be +defined to the set of device driver entries that will be placed in the +table at the *FRONT* of the Device Driver Table and initialized before +any other drivers *INCLUDING* any application prerequisite drivers. + +**NOTES:** + +``CONFIGURE_BSP_PREREQUISITE_DRIVERS`` is typically used by BSPs +to configure common infrastructure such as bus controllers or probe +for devices. + +.. COMMENT: === Idle Task Configuration === + +Idle Task Configuration +======================= + +This section defines the IDLE task related configuration parameters +supported by ````. + +.. COMMENT: === CONFIGURE_IDLE_TASK_BODY === + +Specify Application Specific Idle Task Body +------------------------------------------- +.. index:: CONFIGURE_IDLE_TASK_BODY + +*CONSTANT:* + ``CONFIGURE_IDLE_TASK_BODY`` + +*DATA TYPE:* + Function pointer. + +*RANGE:* + Undefined or valid function pointer. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_IDLE_TASK_BODY`` is set to the function name corresponding +to the application specific IDLE thread body. If not specified, the +BSP or RTEMS default IDLE thread body will be used. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_IDLE_TASK_STACK_SIZE === + +Specify Idle Task Stack Size +---------------------------- +.. index:: CONFIGURE_IDLE_TASK_STACK_SIZE + +*CONSTANT:* + ``CONFIGURE_IDLE_TASK_STACK_SIZE`` + +*DATA TYPE:* + Unsigned integer (``size_t``). + +*RANGE:* + Undefined or positive. + +*DEFAULT VALUE:* + The default value is RTEMS_MINIMUM_STACK_SIZE. + +**DESCRIPTION:** + +``CONFIGURE_IDLE_TASK_STACK_SIZE`` is set to the +desired stack size for the IDLE task. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION === + +Specify Idle Task Performs Application Initialization +----------------------------------------------------- +.. index:: CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION + +*CONSTANT:* + ``CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default, the user is assumed + to provide one or more initialization tasks. + +**DESCRIPTION:** + +``CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION`` is set to +indicate that the user has configured *NO* user initialization tasks +or threads and that the user provided IDLE task will perform application +initialization and then transform itself into an IDLE task. + +**NOTES:** + +If you use this option be careful, the user IDLE task *CANNOT* block +at all during the initialization sequence. Further, once application +initialization is complete, it must make itself preemptible and enter +an IDLE body loop. + +The IDLE task must run at the lowest priority of all tasks in the system. + +.. COMMENT: === Scheduler Algorithm Configuration === + +Scheduler Algorithm Configuration +================================= + +This section defines the configuration parameters related to selecting a +scheduling algorithm for an application. For the schedulers built into +RTEMS, the configuration is straightforward. All that is required is +to define the configuration macro which specifies which scheduler you +want for in your application. The currently available schedulers are: + +The pluggable scheduler interface also enables the user to provide their +own scheduling algorithm. If you choose to do this, you must define +multiple configuration macros. + +.. COMMENT: === CONFIGURE_SCHEDULER_PRIORITY === + +Use Deterministic Priority Scheduler +------------------------------------ +.. index:: CONFIGURE_SCHEDULER_PRIORITY + +*CONSTANT:* + ``CONFIGURE_SCHEDULER_PRIORITY`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is defined by default. + This is the default scheduler and specifying this + configuration parameter is redundant. + +**DESCRIPTION:** + +The Deterministic Priority Scheduler is the default scheduler in RTEMS +for uni-processor applications and is designed for predictable performance +under the highest loads. It can block or unblock a thread in a constant +amount of time. This scheduler requires a variable amount of memory +based upon the number of priorities configured in the system. + +**NOTES:** + +This scheduler may be explicitly selected by defining``CONFIGURE_SCHEDULER_PRIORITY`` although this is equivalent to the +default behavior. + +.. COMMENT: === CONFIGURE_SCHEDULER_SIMPLE === + +Use Simple Priority Scheduler +----------------------------- +.. index:: CONFIGURE_SCHEDULER_SIMPLE + +*CONSTANT:* + ``CONFIGURE_SCHEDULER_SIMPLE`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +When defined, the Simple Priority Scheduler is used at the thread +scheduling algorithm. This is an alternative scheduler in RTEMS. +It is designed to provide the same task scheduling behaviour as the +Deterministic Priority Scheduler while being simpler in implementation +and uses less memory for data management. It maintains a single sorted +list of all ready threads. Thus blocking or unblocking a thread is not +a constant time operation with this scheduler. + +This scheduler may be explicitly selected by defining``CONFIGURE_SCHEDULER_SIMPLE``. + +**NOTES:** + +This scheduler is appropriate for use in small systems where RAM is limited. + +.. COMMENT: === CONFIGURE_SCHEDULER_EDF === + +Use Earliest Deadline First Scheduler +------------------------------------- +.. index:: CONFIGURE_SCHEDULER_EDF + +*CONSTANT:* + ``CONFIGURE_SCHEDULER_EDF`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +The Earliest Deadline First Scheduler (EDF) is an alternative scheduler in +RTEMS for uni-processor applications. The EDF schedules tasks with dynamic +priorities equal to deadlines. The deadlines are declared using only +Rate Monotonic manager which handles periodic behavior. Period is always +equal to deadline. If a task does not have any deadline declared or the +deadline is cancelled, the task is considered a background task which is +scheduled in case no deadline-driven tasks are ready to run. Moreover, +multiple background tasks are scheduled according their priority assigned +upon initialization. All ready tasks reside in a single ready queue. + +This scheduler may be explicitly selected by defining``CONFIGURE_SCHEDULER_EDF``. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_SCHEDULER_CBS === + +Use Constant Bandwidth Server Scheduler +--------------------------------------- +.. index:: CONFIGURE_SCHEDULER_CBS + +*CONSTANT:* + ``CONFIGURE_SCHEDULER_CBS`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +The Constant Bandwidth Server Scheduler (CBS) is an alternative scheduler +in RTEMS for uni-processor applications. The CBS is a budget aware extension +of EDF scheduler. The goal of this scheduler is to ensure temporal +isolation of tasks. The CBS is equipped with a set of additional rules +and provides with an extensive API. + +This scheduler may be explicitly selected by defining``CONFIGURE_SCHEDULER_CBS``. + +.. COMMENT: XXX - add cross reference to API chapter + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_SCHEDULER_PRIORITY_SMP === + +Use Deterministic Priority SMP Scheduler +---------------------------------------- +.. index:: CONFIGURE_SCHEDULER_PRIORITY_SMP + +*CONSTANT:* + ``CONFIGURE_SCHEDULER_PRIORITY_SMP`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +The Deterministic Priority SMP Scheduler is derived from the Deterministic +Priority Scheduler but is capable of scheduling threads across multiple +processors. + +In a configuration with SMP enabled at configure time, it may be +explicitly selected by defining ``CONFIGURE_SCHEDULER_PRIORITY_SMP``. + +**NOTES:** + +This scheduler is only available when RTEMS is configured with SMP +support enabled. + +This scheduler is currently the default in SMP configurations and is +only selected when ``CONFIGURE_SMP_APPLICATION`` is defined. + +.. COMMENT: === CONFIGURE_SCHEDULER_SIMPLE_SMP === + +Use Simple SMP Priority Scheduler +--------------------------------- +.. index:: CONFIGURE_SCHEDULER_SIMPLE_SMP + +*CONSTANT:* + ``CONFIGURE_SCHEDULER_SIMPLE_SMP`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +The Simple SMP Priority Scheduler is derived from the Simple Priority +Scheduler but is capable of scheduling threads across multiple processors. +It is designed to provide the same task scheduling behaviour as the +Deterministic Priority Scheduler while distributing threads across +multiple processors. Being based upon the Simple Priority Scheduler, it also +maintains a single sorted list of all ready threads. Thus blocking or +unblocking a thread is not a constant time operation with this scheduler. + +In addition, when allocating threads to processors, the algorithm is not +constant time. This algorithm was not designed with efficiency as a +primary design goal. Its primary design goal was to provide an SMP-aware +scheduling algorithm that is simple to understand. + +In a configuration with SMP enabled at configure time, it may be +explicitly selected by defining ``CONFIGURE_SCHEDULER_SIMPLE_SMP``. + +**NOTES:** + +This scheduler is only available when RTEMS is configured with SMP +support enabled. + +.. COMMENT: === Configuring a Scheduler Name === + +Configuring a Scheduler Name +---------------------------- +.. index:: CONFIGURE_SCHEDULER_NAME + +*CONSTANT:* + ``CONFIGURE_SCHEDULER_NAME`` + +*DATA TYPE:* + RTEMS Name (``rtems_name``). + +*RANGE:* + Any value. + +*DEFAULT VALUE:* + The default name is + - ``"UCBS"`` for the Uni-Processor CBS scheduler, + - ``"UEDF"`` for the Uni-Processor EDF scheduler, + - ``"UPD "`` for the Uni-Processor Deterministic Priority scheduler, + - ``"UPS "`` for the Uni-Processor Simple Priority scheduler, + - ``"MPA "`` for the Multi-Processor Priority Affinity scheduler, and + - ``"MPD "`` for the Multi-Processor Deterministic Priority scheduler, and + - ``"MPS "`` for the Multi-Processor Simple Priority scheduler. + +**DESCRIPTION:** + +Schedulers can be identified via ``rtems_scheduler_ident``. The name of the scheduler is determined by the configuration. + +**NOTES:** + +None. + +.. COMMENT: === Configuring a User Scheduler === + +Configuring a User Provided Scheduler +------------------------------------- +.. index:: CONFIGURE_SCHEDULER_USER + +*CONSTANT:* + ``CONFIGURE_SCHEDULER_USER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +RTEMS allows the application to provide its own task/thread +scheduling algorithm. In order to do this, one must define``CONFIGURE_SCHEDULER_USER`` to indicate the application provides its +own scheduling algorithm. If ``CONFIGURE_SCHEDULER_USER`` is defined +then the following additional macros must be defined: + +- ``CONFIGURE_SCHEDULER_CONTEXT`` must be defined to a static definition + of the scheduler context of the user scheduler. + +- ``CONFIGURE_SCHEDULER_CONTROLS`` must be defined to a scheduler + control initializer for the user scheduler. + +- ``CONFIGURE_SCHEDULER_USER_PER_THREAD`` must be defined to the type of + the per-thread information of the user scheduler. + +**NOTES:** + +At this time, the mechanics and requirements for writing a +new scheduler are evolving and not fully documented. It is +recommended that you look at the existing Deterministic Priority +Scheduler in ``cpukit/score/src/schedulerpriority*.c`` for +guidance. For guidance on the configuration macros, please examine``cpukit/sapi/include/confdefs.h`` for how these are defined for the +Deterministic Priority Scheduler. + +.. COMMENT: === Configuring Clustered Schedulers === + + +Configuring Clustered Schedulers +-------------------------------- + +Clustered scheduling helps to control the worst-case latencies in a +multi-processor system. The goal is to reduce the amount of shared state in +the system and thus prevention of lock contention. Modern multi-processor +systems tend to have several layers of data and instruction caches. With +clustered scheduling it is possible to honour the cache topology of a system +and thus avoid expensive cache synchronization traffic. + +We have clustered scheduling in case the set of processors of a system is +partitioned into non-empty pairwise-disjoint subsets. These subsets are called +clusters. Clusters with a cardinality of one are partitions. Each cluster is +owned by exactly one scheduler instance. In order to use clustered +scheduling the application designer has to answer two questions. + +# How is the set of processors partitioned into clusters? + +# Which scheduler is used for which cluster? + +**CONFIGURATION:** + +The schedulers in an SMP system are statically configured on RTEMS. Firstly +the application must select which scheduling algorithms are available with the +following defines + +- ``CONFIGURE_SCHEDULER_PRIORITY_SMP``, + +- ``CONFIGURE_SCHEDULER_SIMPLE_SMP``, and + +- ``CONFIGURE_SCHEDULER_PRIORITY_AFFINITY_SMP``. + +This is necessary to calculate the per-thread overhead introduced by the +schedulers. After these definitions the configuration file must ``#include +`` to have access to scheduler specific configuration macros. +Each scheduler needs a context to store state information at run-time. To +provide a context for each scheduler is the next step. Use the following +macros to create scheduler contexts + +- ``RTEMS_SCHEDULER_CONTEXT_PRIORITY_SMP(name, prio_count)``, + +- ``RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP(name)``, and + +- ``RTEMS_SCHEDULER_CONTEXT_PRIORITY_AFFINITY_SMP(name, prio_count)``. + +The ``name`` parameter is used as part of a designator for a global +variable, so the usual C/C++ designator rules apply. Additional parameters are +scheduler specific. The schedulers are registered in the system via the +scheduler table. To create the scheduler table define``CONFIGURE_SCHEDULER_CONTROLS`` to a list of the following scheduler +control initializers + +- ``RTEMS_SCHEDULER_CONTROL_PRIORITY_SMP(name, obj_name)``, + +- ``RTEMS_SCHEDULER_CONTROL_SIMPLE_SMP(name, obj_name)``, and + +- ``RTEMS_SCHEDULER_CONTROL_PRIORITY_AFFINITY_SMP(name, obj_name)``. + +The ``name`` parameter must correspond to the parameter defining the +scheduler context. The ``obj_name`` determines the scheduler object name +and can be used in ``rtems_scheduler_ident()`` to get the scheduler object +identifier. + +The last step is to define which processor uses which scheduler. +For this purpose a scheduler assignment table must be defined. The entry count +of this table must be equal to the configured maximum processors +(``CONFIGURE_SMP_MAXIMUM_PROCESSORS``). A processor assignment to a +scheduler can be optional or mandatory. The boot processor must have a +scheduler assigned. In case the system needs more mandatory processors than +available then a fatal run-time error will occur. To specify the scheduler +assignments define ``CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS`` to a list of``RTEMS_SCHEDULER_ASSIGN(index, attr)`` and``RTEMS_SCHEDULER_ASSIGN_NO_SCHEDULER`` macros. The ``index`` parameter +must be a valid index into the scheduler table. The ``attr`` parameter +defines the scheduler assignment attributes. By default a scheduler assignment +to a processor is optional. For the scheduler assignment attribute use one of +the mutually exclusive variants + +- ``RTEMS_SCHEDULER_ASSIGN_DEFAULT``, + +- ``RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY``, and + +- ``RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL``. + +**ERRORS:** + +In case one of the scheduler indices in``CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS`` is invalid a link-time error will +occur with an undefined reference to ``RTEMS_SCHEDULER_INVALID_INDEX``. + +Some fatal errors may occur in case of scheduler configuration inconsistencies or a lack +of processors on the system. The fatal source is``RTEMS_FATAL_SOURCE_SMP``. None of the errors is internal. + +- ``SMP_FATAL_BOOT_PROCESSOR_NOT_ASSIGNED_TO_SCHEDULER`` - the boot + processor must have a scheduler assigned. + +- ``SMP_FATAL_MANDATORY_PROCESSOR_NOT_PRESENT`` - there exists a + mandatory processor beyond the range of physically or virtually available + processors. The processor demand must be reduced for this system. + +- ``SMP_FATAL_START_OF_MANDATORY_PROCESSOR_FAILED`` - the start of a + mandatory processor failed during system initialization. The system may not + have this processor at all or it could be a problem with a boot loader for + example. Check the ``CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS`` definition. + +- ``SMP_FATAL_MULTITASKING_START_ON_UNASSIGNED_PROCESSOR`` - it is not + allowed to start multitasking on a processor with no scheduler assigned. + +**EXAMPLE:** + +The following example shows a scheduler configuration for a hypothetical +product using two chip variants. One variant has four processors which is used +for the normal product line and another provides eight processors for the +high-performance product line. The first processor performs hard-real time +control of actuators and sensors. The second processor is not used by RTEMS at +all and runs a Linux instance to provide a graphical user interface. The +additional processors are used for a worker thread pool to perform data +processing operations. + +The processors managed by RTEMS use two Deterministic Priority scheduler +instances capable of dealing with 256 priority levels. The scheduler with +index zero has the name ``"IO "``. The scheduler with index one has the +name ``"WORK"``. The scheduler assignments of the first, third and fourth +processor are mandatory, so the system must have at least four processors, +otherwise a fatal run-time error will occur during system startup. The +processor assignments for the fifth up to the eighth processor are optional so +that the same application can be used for the normal and high-performance +product lines. The second processor has no scheduler assigned and runs Linux. +A hypervisor will ensure that the two systems cannot interfere in an +undesirable way. +.. code:: c + + #define CONFIGURE_SMP_MAXIMUM_PROCESSORS 8 + #define CONFIGURE_MAXIMUM_PRIORITY 255 + /* Make the scheduler algorithm available \*/ + #define CONFIGURE_SCHEDULER_PRIORITY_SMP + #include + /* Create contexts for the two scheduler instances \*/ + RTEMS_SCHEDULER_CONTEXT_PRIORITY_SMP(io, CONFIGURE_MAXIMUM_PRIORITY + 1); + RTEMS_SCHEDULER_CONTEXT_PRIORITY_SMP(work, CONFIGURE_MAXIMUM_PRIORITY + 1); + /* Define the scheduler table \*/ + #define CONFIGURE_SCHEDULER_CONTROLS \\ + RTEMS_SCHEDULER_CONTROL_PRIORITY_SMP( \\ + io, \\ + rtems_build_name('I', 'O', ' ', ' ') \\ + ), \\ + RTEMS_SCHEDULER_CONTROL_PRIORITY_SMP( \\ + work, \\ + rtems_build_name('W', 'O', 'R', 'K') \\ + ) + /* Define the processor to scheduler assignments \*/ + #define CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS \\ + RTEMS_SCHEDULER_ASSIGN(0, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \\ + RTEMS_SCHEDULER_ASSIGN_NO_SCHEDULER, \\ + RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \\ + RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \\ + RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL), \\ + RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL), \\ + RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL), \\ + RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_OPTIONAL) + +.. COMMENT: === SMP Specific Configuration Parameters === + +SMP Specific Configuration Parameters +===================================== + +When RTEMS is configured to support SMP target systems, there are other +configuration parameters which apply. + +.. COMMENT: XXX - add -enable-smp + +.. COMMENT: === CONFIGURE_SMP_APPLICATION === + + +Enable SMP Support for Applications +----------------------------------- +.. index:: CONFIGURE_SMP_APPLICATION + +*CONSTANT:* + ``CONFIGURE_SMP_APPLICATION`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_SMP_APPLICATION`` must be defined to enable SMP support for the +application. + +**NOTES:** + +This define may go away in the future in case all RTEMS components are SMP +ready. This configuration define is ignored on uni-processor configurations. + +.. COMMENT: === CONFIGURE_SMP_MAXIMUM_PROCESSORS === + +Specify Maximum Processors in SMP System +---------------------------------------- +.. index:: CONFIGURE_SMP_MAXIMUM_PROCESSORS + +*CONSTANT:* + ``CONFIGURE_SMP_MAXIMUM_PROCESSORS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + The default value is 1, (if CONFIGURE_SMP_APPLICATION is defined). + +**DESCRIPTION:** + +``CONFIGURE_SMP_MAXIMUM_PROCESSORS`` must be set to the number of +processors in the SMP configuration. + +**NOTES:** + +If there are more processors available than configured, the rest will be +ignored. This configuration define is ignored on uni-processor configurations. + +.. COMMENT: === Device Driver Table === + +Device Driver Table +=================== + +This section defines the configuration parameters related +to the automatic generation of a Device Driver Table. As```` only is aware of a small set of +standard device drivers, the generated Device Driver +Table is suitable for simple applications with no +custom device drivers. + +Note that network device drivers are not configured in the Device Driver Table. + +.. COMMENT: === CONFIGURE_MAXIMUM_DRIVERS === + +Specifying the Maximum Number of Device Drivers +----------------------------------------------- +.. index:: CONFIGURE_MAXIMUM_DRIVERS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_DRIVERS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + This is computed by default, and is set to the number of device drivers + configured using the ``CONFIGURE_APPLICATIONS_NEEDS_XXX_DRIVER`` + configuration parameters. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_DRIVERS`` is defined as the number of device +drivers per node. + +**NOTES:** + +If the application will dynamically install device drivers, then this +configuration parameter must be larger than the number of statically +configured device drivers. Drivers configured using the``CONFIGURE_APPLICATIONS_NEEDS_XXX_DRIVER`` configuration parameters +are statically installed. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER === + +Enable Console Device Driver +---------------------------- +.. index:: CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER`` is defined if the +application wishes to include the Console Device Driver. + +**NOTES:** + +This device driver is responsible for providing standard input and output +using */dev/console*. + +BSPs should be constructed in a manner that allows ``printk()`` +to work properly without the need for the console driver to be configured. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER === + +Enable Clock Driver +------------------- +.. index:: CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER`` is defined if the +application wishes to include the Clock Device Driver. + +**NOTES:** + +This device driver is responsible for providing a regular +interrupt which invokes the ``rtems_clock_tick`` directive. + +If neither the Clock Driver not Benchmark Timer is enabled and +the configuration parameter``CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER`` is not defined, +then a compile time error will occur. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER === + +Enable the Benchmark Timer Driver +--------------------------------- +.. index:: CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER`` is defined if the +application wishes to include the Timer Driver. This device driver is +used to benchmark execution times by the RTEMS Timing Test Suites. + +**NOTES:** + +If neither the Clock Driver not Benchmark Timer is enabled and +the configuration parameter``CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER`` is not defined, +then a compile time error will occur. + +.. COMMENT: === CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER === + +Specify Clock and Benchmark Timer Drivers Are Not Needed +-------------------------------------------------------- +.. index:: CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER + +*CONSTANT:* + ``CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_DOES_NOT_NEED_CLOCK_DRIVER`` is defined when +the application does *NOT* want the Clock Device Driver and is *NOT* +using the Timer Driver. The inclusion or exclusion of the Clock Driver +must be explicit in user applications. + +**NOTES:** + +This configuration parameter is intended to prevent the common user error +of using the Hello World example as the baseline for an application and +leaving out a clock tick source. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER === + +Enable Real-Time Clock Driver +----------------------------- +.. index:: CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_NEEDS_RTC_DRIVER`` is defined if the +application wishes to include the Real-Time Clock Driver. + +**NOTES:** + +Most BSPs do not include support for a real-time clock. This is because +many boards do not include the required hardware. + +If this is defined and the BSP does not have this device driver, then +the user will get a link time error for an undefined symbol. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER === + +Enable the Watchdog Device Driver +--------------------------------- +.. index:: CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_NEEDS_WATCHDOG_DRIVER`` +is defined if the application wishes to include the Watchdog Driver. + +**NOTES:** + +Most BSPs do not include support for a watchdog device driver. This is +because many boards do not include the required hardware. + +If this is defined and the BSP does not have this device driver, then +the user will get a link time error for an undefined symbol. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER === + +Enable the Graphics Frame Buffer Device Driver +---------------------------------------------- +.. index:: CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_NEEDS_FRAME_BUFFER_DRIVER`` is defined +if the application wishes to include the BSP’s Frame Buffer Device Driver. + +**NOTES:** + +Most BSPs do not include support for a Frame Buffer Device Driver. This is +because many boards do not include the required hardware. + +If this is defined and the BSP does not have this device driver, then +the user will get a link time error for an undefined symbol. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER === + +Enable Stub Device Driver +------------------------- +.. index:: CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER`` is defined if the +application wishes to include the Stub Device Driver. + +**NOTES:** + +This device driver simply provides entry points that return successful +and is primarily a test fixture. It is supported by all BSPs. + +.. COMMENT: === CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS === + +Specify Application Prerequisite Device Drivers +----------------------------------------------- +.. index:: CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS + +*CONSTANT:* + ``CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS`` + +*DATA TYPE:* + device driver entry structures + +*RANGE:* + Undefined or set of device driver entry structures + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_PREREQUISITE_DRIVERS`` is defined if the +application has device drivers it needs to include in the Device Driver +Table. This should be defined to the set of device driver entries that +will be placed in the table at the *FRONT* of the Device Driver Table +and initialized before any other drivers *EXCEPT* any BSP prerequisite +drivers. + +**NOTES:** + +In some cases, it is used by System On Chip BSPs to support peripheral +buses beyond those normally found on the System On Chip. For example, +this is used by one RTEMS system which has implemented a SPARC/ERC32 +based board with VMEBus. The VMEBus Controller initialization is performed +by a device driver configured via this configuration parameter. + +.. COMMENT: XXX Add example + +.. COMMENT: === CONFIGURE_APPLICATION_EXTRA_DRIVERS === + +Specify Extra Application Device Drivers +---------------------------------------- +.. index:: CONFIGURE_APPLICATION_EXTRA_DRIVERS + +*CONSTANT:* + ``CONFIGURE_APPLICATION_EXTRA_DRIVERS`` + +*DATA TYPE:* + device driver entry structures + +*RANGE:* + Undefined or set of device driver entry structures + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_APPLICATION_EXTRA_DRIVERS`` is defined if the +application has device drivers it needs to include in the Device Driver +Table. This should be defined to the set of device driver entries that +will be placed in the table at the *END* of the Device Driver Table. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER === + +Enable /dev/null Device Driver +------------------------------ +.. index:: CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER +.. index:: /dev/null + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +This configuration variable is specified to enable */dev/null* +device driver. + +**NOTES:** + +This device driver is supported by all BSPs. + +.. COMMENT: === CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER === + +Enable /dev/zero Device Driver +------------------------------ +.. index:: CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER +.. index:: /dev/zero + +*CONSTANT:* + ``CONFIGURE_APPLICATION_NEEDS_ZERO_DRIVER`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +This configuration variable is specified to enable */dev/zero* +device driver. + +**NOTES:** + +This device driver is supported by all BSPs. + +.. COMMENT: === CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE === + +Specifying Application Defined Device Driver Table +-------------------------------------------------- +.. index:: CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE + +*CONSTANT:* + ``CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default, indicating the ```` + is providing the device driver table. + +**DESCRIPTION:** + +``CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE`` is defined if the application +wishes to provide their own Device Driver Table. + +The table must be an array of ``rtems_driver_address_table`` entries named``_IO_Driver_address_table``. The application must also provide a const +variable ``_IO_Number_of_drivers`` of type ``size_t`` indicating the +number of entries in the ``_IO_Driver_address_table``. + +**NOTES:** + +It is expected that there the application would only rarely need to do this. + +.. COMMENT: === Multiprocessing Configuration === + +Multiprocessing Configuration +============================= + +This section defines the multiprocessing related system configuration +parameters supported by ````. They are only used +if the Multiprocessing Support (distinct from the SMP support) is enabled +at configure time using the ``--enable-multiprocessing`` option. + +Additionally, this class of Configuration Constants are only applicable if``CONFIGURE_MP_APPLICATION`` is defined. + +.. COMMENT: === CONFIGURE_MP_APPLICATION === + +Specify Application Will Use Multiprocessing +-------------------------------------------- +.. index:: CONFIGURE_MP_APPLICATION + +*CONSTANT:* + ``CONFIGURE_MP_APPLICATION`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +This configuration parameter must be defined to indicate +that the application intends to be part of a multiprocessing +configuration. Additional configuration parameters are assumed to be +provided. + +**NOTES:** + +This has no impact unless RTEMS was configured and built using the``--enable-multiprocessing`` option. + +.. COMMENT: === CONFIGURE_MP_NODE_NUMBER === + +Configure Node Number in Multiprocessor Configuration +----------------------------------------------------- +.. index:: CONFIGURE_MP_NODE_NUMBER + +*CONSTANT:* + ``CONFIGURE_MP_NODE_NUMBER`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is ``NODE_NUMBER``, which is assumed to be + set by the compilation environment. + +**DESCRIPTION:** + +``CONFIGURE_MP_NODE_NUMBER`` is the node number of +this node in a multiprocessor system. + +**NOTES:** + +In the RTEMS Multiprocessing Test Suite, the node number is derived from +the Makefile variable ``NODE_NUMBER``. The same code is compiled with +the ``NODE_NUMBER`` set to different values. The test programs behave +differently based upon their node number. + +.. COMMENT: === CONFIGURE_MP_MAXIMUM_NODES === + +Configure Maximum Node in Multiprocessor Configuration +------------------------------------------------------ +.. index:: CONFIGURE_MP_MAXIMUM_NODES + +*CONSTANT:* + ``CONFIGURE_MP_MAXIMUM_NODES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is 2. + +**DESCRIPTION:** + +``CONFIGURE_MP_MAXIMUM_NODES`` is the maximum number of nodes in a +multiprocessor system. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS === + +Configure Maximum Global Objects in Multiprocessor Configuration +---------------------------------------------------------------- +.. index:: CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS + +*CONSTANT:* + ``CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Positive. + +*DEFAULT VALUE:* + The default value is 32. + +**DESCRIPTION:** + +``CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS`` is the maximum number of +concurrently active global objects in a multiprocessor system. + +**NOTES:** + +This value corresponds to the total number of objects which can be +created with the ``RTEMS_GLOBAL`` attribute. + +.. COMMENT: === CONFIGURE_MP_MAXIMUM_PROXIES === + +Configure Maximum Proxies in Multiprocessor Configuration +--------------------------------------------------------- +.. index:: CONFIGURE_MP_MAXIMUM_PROXIES + +*CONSTANT:* + ``CONFIGURE_MP_MAXIMUM_PROXIES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Undefined or positive. + +*DEFAULT VALUE:* + The default value is 32. + +**DESCRIPTION:** + +``CONFIGURE_MP_MAXIMUM_PROXIES`` is the maximum number of concurrently +active thread/task proxies on this node in a multiprocessor system. + +**NOTES:** + +Since a proxy is used to represent a remote task/thread which is blocking on +this node. This configuration parameter reflects the maximum number of +remote tasks/threads which can be blocked on objects on this node. + +.. COMMENT: XXX - add xref to proxy discussion in MP chapter + +.. COMMENT: === CONFIGURE_MP_MPCI_TABLE_POINTER === + +Configure MPCI in Multiprocessor Configuration +---------------------------------------------- +.. index:: CONFIGURE_MP_MPCI_TABLE_POINTER + +*CONSTANT:* + ``CONFIGURE_MP_MPCI_TABLE_POINTER`` + +*DATA TYPE:* + pointer to ``rtems_mpci_table`` + +*RANGE:* + undefined or valid pointer + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_MP_MPCI_TABLE_POINTER`` is the pointer to the +MPCI Configuration Table. The default value of this field is``&MPCI_table``. + +**NOTES:** + +RTEMS provides a Shared Memory MPCI Device Driver which can be used on +any Multiprocessor System assuming the BSP provides the proper set of +supporting methods. + +.. COMMENT: === CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE === + +Do Not Generate Multiprocessor Configuration Table +-------------------------------------------------- +.. index:: CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE + +*CONSTANT:* + ``CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE`` is defined if the +application wishes to provide their own Multiprocessing Configuration +Table. The generated table is named ``Multiprocessing_configuration``. + +**NOTES:** + +This is a configuration parameter which is very unlikely to be used by +an application. If you find yourself wanting to use it in an application, +please reconsider and discuss this on the RTEMS Users mailing list. + +.. COMMENT: === Ada Tasks === + +Ada Tasks +========= + +This section defines the system configuration parameters supported +by ```` related to configuring RTEMS to support +a task using Ada tasking with GNAT/RTEMS. + +These configuration parameters are only available when RTEMS is built with +the ``--enable-ada`` configure option and the application specifies``CONFIGURE_GNAT_RTEMS``. + +Additionally RTEMS includes an Ada language binding to the Classic +API which has a test suite. This test suite is enabled only when``--enable-tests`` and ``--enable-expada`` are specified on the +configure command. + +.. COMMENT: === CONFIGURE_GNAT_RTEMS === + +Specify Application Includes Ada Code +------------------------------------- +.. index:: CONFIGURE_GNAT_RTEMS + +*CONSTANT:* + ``CONFIGURE_GNAT_RTEMS`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_GNAT_RTEMS`` is defined to inform RTEMS that the GNAT +Ada run-time is to be used by the application. + +**NOTES:** + +This configuration parameter is critical as it makes```` configure the resources (POSIX API Threads, +Mutexes, Condition Variables, and Keys) used implicitly by the GNAT +run-time. + +.. COMMENT: === CONFIGURE_MAXIMUM_ADA_TASKS === + +Specify the Maximum Number of Ada Tasks. +---------------------------------------- +.. index:: CONFIGURE_MAXIMUM_ADA_TASKS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_ADA_TASKS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Undefined or positive. + +*DEFAULT VALUE:* + If ``CONFIGURE_GNAT_RTEMS`` is defined, then the + default value is 20, otherwise the default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_ADA_TASKS`` is the number of Ada tasks that can +be concurrently active in the system. + +**NOTES:** + +None. + +.. COMMENT: === CONFIGURE_MAXIMUM_FAKE_ADA_TASKS === + +Specify the Maximum Fake Ada Tasks +---------------------------------- +.. index:: CONFIGURE_MAXIMUM_FAKE_ADA_TASKS + +*CONSTANT:* + .. index:: ``CONFIGURE_MAXIMUM_FAKE_ADA_TASKS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 0. + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_FAKE_ADA_TASKS`` is the number of *fake* Ada tasks +that can be concurrently active in the system. A *fake* Ada task is +a non-Ada task that makes calls back into Ada code and thus implicitly +uses the Ada run-time. + +**NOTES:** + +None. + +.. COMMENT: === PCI Library === + +PCI Library +=========== + +This section defines the system configuration parameters supported +by ``rtems/confdefs.h`` related to configuring the PCI Library +for RTEMS. + +The PCI Library startup behaviour can be configured in four different +ways depending on how ``CONFIGURE_PCI_CONFIG_LIB`` is defined: + +- .. index:: PCI_LIB_AUTO + + ``PCI_LIB_AUTO`` is used to enable the PCI auto configuration + software. PCI will be automatically probed, PCI buses enumerated, all + devices and bridges will be initialized using Plug & Play software + routines. The PCI device tree will be populated based on the PCI devices + found in the system, PCI devices will be configured by allocating address + region resources automatically in PCI space according to the BSP or host + bridge driver set up. + +- .. index:: PCI_LIB_READ + + ``PCI_LIB_READ`` is used to enable the PCI read configuration + software. The current PCI configuration is read to create the RAM + representation (the PCI device tree) of the PCI devices present. PCI devices + are assumed to already have been initialized and PCI buses enumerated, it is + therefore required that a BIOS or a boot loader has set up configuration space + prior to booting into RTEMS. + +- .. index:: PCI_LIB_STATIC + + ``PCI_LIB_STATIC`` is used to enable the PCI static configuration + software. The user provides a PCI tree with information how all PCI devices + are to be configured at compile time by linking in a custom``struct pci_bus pci_hb`` tree. The static PCI library will not probe PCI + for devices, instead it will assume that all devices defined by the user are + present, it will enumerate the PCI buses and configure all PCI devices in + static configuration accordingly. Since probe and allocation software is not + needed the startup is faster, has smaller footprint and does not require + dynamic memory allocation. + +- .. index:: PCI_LIB_PERIPHERAL + + ``PCI_LIB_PERIPHERAL`` is used to enable the PCI peripheral + configuration. It is similar to ``PCI_LIB_STATIC``, but it will never write + the configuration to the PCI devices since PCI peripherals are not allowed to + access PCI configuration space. + +Note that selecting PCI_LIB_STATIC or PCI_LIB_PERIPHERAL but not defining``pci_hb`` will reuslt in link errors. Note also that in these modes +Plug & Play is not performed. + +.. COMMENT: === Go Tasks === + +Go Tasks +======== + +.. COMMENT: === CONFIGURE_ENABLE_GO === + +Specify Application Includes Go Code +------------------------------------ +.. index:: CONFIGURE_ENABLE_GO + +*CONSTANT:* + ``CONFIGURE_ENABLE_GO`` + +*DATA TYPE:* + Boolean feature macro. + +*RANGE:* + Defined or undefined. + +*DEFAULT VALUE:* + This is not defined by default. + +**DESCRIPTION:** + +``CONFIGURE_ENABLE_GO`` is defined to inform RTEMS that the Go +run-time is to be used by the application. + +**NOTES:** + +The Go language support is experimental + +.. COMMENT: === CONFIGURE_MAXIMUM_GOROUTINES === + +Specify the maximum number of Go routines +----------------------------------------- +.. index:: CONFIGURE_MAXIMUM_GOROUTINES + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_GOROUTINES`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 400 + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_GOROUTINES`` is defined to specify the maximum number of +Go routines. + +**NOTES:** + +The Go language support is experimental + +.. COMMENT: === CONFIGURE_MAXIMUM_GO_CHANNELS === + +Specify the maximum number of Go Channels +----------------------------------------- +.. index:: CONFIGURE_MAXIMUM_GO_CHANNELS + +*CONSTANT:* + ``CONFIGURE_MAXIMUM_GO_CHANNELS`` + +*DATA TYPE:* + Unsigned integer (``uint32_t``). + +*RANGE:* + Zero or positive. + +*DEFAULT VALUE:* + The default value is 500 + +**DESCRIPTION:** + +``CONFIGURE_MAXIMUM_GO_CHANNELS`` is defined to specify the maximum number +of Go channels. + +**NOTES:** + +The Go language support is experimental + +.. COMMENT: === Configuration Data Structures === + +Configuration Data Structures +============================= + +It is recommended that applications be configured using```` as it is simpler and insulates applications +from changes in the underlying data structures. However, it is sometimes +important to understand the data structures that are automatically filled +in by the configuration parameters. This section describes the primary +configuration data structures. + +If the user wishes to see the details of a particular data structure, +they are are advised to look at the source code. After all, that is one +of the advantages of RTEMS. + +.. COMMENT: COPYRIGHT (c) 1988-2007. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Multiprocessing Manager +####################### + +.. index:: multiprocessing + +Introduction +============ + +In multiprocessor real-time systems, new +requirements, such as sharing data and global resources between +processors, are introduced. This requires an efficient and +reliable communications vehicle which allows all processors to +communicate with each other as necessary. In addition, the +ramifications of multiple processors affect each and every +characteristic of a real-time system, almost always making them +more complicated. + +RTEMS addresses these issues by providing simple and +flexible real-time multiprocessing capabilities. The executive +easily lends itself to both tightly-coupled and loosely-coupled +configurations of the target system hardware. In addition, +RTEMS supports systems composed of both homogeneous and +heterogeneous mixtures of processors and target boards. + +A major design goal of the RTEMS executive was to +transcend the physical boundaries of the target hardware +configuration. This goal is achieved by presenting the +application software with a logical view of the target system +where the boundaries between processor nodes are transparent. +As a result, the application developer may designate objects +such as tasks, queues, events, signals, semaphores, and memory +blocks as global objects. These global objects may then be +accessed by any task regardless of the physical location of the +object and the accessing task. RTEMS automatically determines +that the object being accessed resides on another processor and +performs the actions required to access the desired object. +Simply stated, RTEMS allows the entire system, both hardware and +software, to be viewed logically as a single system. + +Background +========== + +.. index:: multiprocessing topologies + +RTEMS makes no assumptions regarding the connection +media or topology of a multiprocessor system. The tasks which +compose a particular application can be spread among as many +processors as needed to satisfy the application’s timing +requirements. The application tasks can interact using a subset +of the RTEMS directives as if they were on the same processor. +These directives allow application tasks to exchange data, +communicate, and synchronize regardless of which processor they +reside upon. + +The RTEMS multiprocessor execution model is multiple +instruction streams with multiple data streams (MIMD). This +execution model has each of the processors executing code +independent of the other processors. Because of this +parallelism, the application designer can more easily guarantee +deterministic behavior. + +By supporting heterogeneous environments, RTEMS +allows the systems designer to select the most efficient +processor for each subsystem of the application. Configuring +RTEMS for a heterogeneous environment is no more difficult than +for a homogeneous one. In keeping with RTEMS philosophy of +providing transparent physical node boundaries, the minimal +heterogeneous processing required is isolated in the MPCI layer. + +Nodes +----- +.. index:: nodes, definition + +A processor in a RTEMS system is referred to as a +node. Each node is assigned a unique non-zero node number by +the application designer. RTEMS assumes that node numbers are +assigned consecutively from one to the ``maximum_nodes`` +configuration parameter. The node +number, node, and the maximum number of nodes, maximum_nodes, in +a system are found in the Multiprocessor Configuration Table. +The maximum_nodes field and the number of global objects, +maximum_global_objects, is required to be the same on all nodes +in a system. + +The node number is used by RTEMS to identify each +node when performing remote operations. Thus, the +Multiprocessor Communications Interface Layer (MPCI) must be +able to route messages based on the node number. + +Global Objects +-------------- +.. index:: global objects, definition + +All RTEMS objects which are created with the GLOBAL +attribute will be known on all other nodes. Global objects can +be referenced from any node in the system, although certain +directive specific restrictions (e.g. one cannot delete a remote +object) may apply. A task does not have to be global to perform +operations involving remote objects. The maximum number of +global objects is the system is user configurable and can be +found in the maximum_global_objects field in the Multiprocessor +Configuration Table. The distribution of tasks to processors is +performed during the application design phase. Dynamic task +relocation is not supported by RTEMS. + +Global Object Table +------------------- +.. index:: global objects table + +RTEMS maintains two tables containing object +information on every node in a multiprocessor system: a local +object table and a global object table. The local object table +on each node is unique and contains information for all objects +created on this node whether those objects are local or global. +The global object table contains information regarding all +global objects in the system and, consequently, is the same on +every node. + +Since each node must maintain an identical copy of +the global object table, the maximum number of entries in each +copy of the table must be the same. The maximum number of +entries in each copy is determined by the +maximum_global_objects parameter in the Multiprocessor +Configuration Table. This parameter, as well as the +maximum_nodes parameter, is required to be the same on all +nodes. To maintain consistency among the table copies, every +node in the system must be informed of the creation or deletion +of a global object. + +Remote Operations +----------------- +.. index:: MPCI and remote operations + +When an application performs an operation on a remote +global object, RTEMS must generate a Remote Request (RQ) message +and send it to the appropriate node. After completing the +requested operation, the remote node will build a Remote +Response (RR) message and send it to the originating node. +Messages generated as a side-effect of a directive (such as +deleting a global task) are known as Remote Processes (RP) and +do not require the receiving node to respond. + +Other than taking slightly longer to execute +directives on remote objects, the application is unaware of the +location of the objects it acts upon. The exact amount of +overhead required for a remote operation is dependent on the +media connecting the nodes and, to a lesser degree, on the +efficiency of the user-provided MPCI routines. + +The following shows the typical transaction sequence +during a remote application: + +# The application issues a directive accessing a + remote global object. + +# RTEMS determines the node on which the object + resides. + +# RTEMS calls the user-provided MPCI routine + GET_PACKET to obtain a packet in which to build a RQ message. + +# After building a message packet, RTEMS calls the + user-provided MPCI routine SEND_PACKET to transmit the packet to + the node on which the object resides (referred to as the + destination node). + +# The calling task is blocked until the RR message + arrives, and control of the processor is transferred to another + task. + +# The MPCI layer on the destination node senses the + arrival of a packet (commonly in an ISR), and calls the``rtems_multiprocessing_announce`` + directive. This directive readies the Multiprocessing Server. + +# The Multiprocessing Server calls the user-provided + MPCI routine RECEIVE_PACKET, performs the requested operation, + builds an RR message, and returns it to the originating node. + +# The MPCI layer on the originating node senses the + arrival of a packet (typically via an interrupt), and calls the RTEMS``rtems_multiprocessing_announce`` directive. This directive + readies the Multiprocessing Server. + +# The Multiprocessing Server calls the user-provided + MPCI routine RECEIVE_PACKET, readies the original requesting + task, and blocks until another packet arrives. Control is + transferred to the original task which then completes processing + of the directive. + +If an uncorrectable error occurs in the user-provided +MPCI layer, the fatal error handler should be invoked. RTEMS +assumes the reliable transmission and reception of messages by +the MPCI and makes no attempt to detect or correct errors. + +Proxies +------- +.. index:: proxy, definition + +A proxy is an RTEMS data structure which resides on a +remote node and is used to represent a task which must block as +part of a remote operation. This action can occur as part of the``rtems_semaphore_obtain`` and``rtems_message_queue_receive`` directives. If the +object were local, the task’s control block would be available +for modification to indicate it was blocking on a message queue +or semaphore. However, the task’s control block resides only on +the same node as the task. As a result, the remote node must +allocate a proxy to represent the task until it can be readied. + +The maximum number of proxies is defined in the +Multiprocessor Configuration Table. Each node in a +multiprocessor system may require a different number of proxies +to be configured. The distribution of proxy control blocks is +application dependent and is different from the distribution of +tasks. + +Multiprocessor Configuration Table +---------------------------------- + +The Multiprocessor Configuration Table contains +information needed by RTEMS when used in a multiprocessor +system. This table is discussed in detail in the section +Multiprocessor Configuration Table of the Configuring a System +chapter. + +Multiprocessor Communications Interface Layer +============================================= + +The Multiprocessor Communications Interface Layer +(MPCI) is a set of user-provided procedures which enable the +nodes in a multiprocessor system to communicate with one +another. These routines are invoked by RTEMS at various times +in the preparation and processing of remote requests. +Interrupts are enabled when an MPCI procedure is invoked. It is +assumed that if the execution mode and/or interrupt level are +altered by the MPCI layer, that they will be restored prior to +returning to RTEMS... index:: MPCI, definition + +The MPCI layer is responsible for managing a pool of +buffers called packets and for sending these packets between +system nodes. Packet buffers contain the messages sent between +the nodes. Typically, the MPCI layer will encapsulate the +packet within an envelope which contains the information needed +by the MPCI layer. The number of packets available is dependent +on the MPCI layer implementation... index:: MPCI entry points + +The entry points to the routines in the user’s MPCI +layer should be placed in the Multiprocessor Communications +Interface Table. The user must provide entry points for each of +the following table entries in a multiprocessor system: + +- initialization initialize the MPCI + +- get_packet obtain a packet buffer + +- return_packet return a packet buffer + +- send_packet send a packet to another node + +- receive_packet called to get an arrived packet + +A packet is sent by RTEMS in each of the following situations: + +- an RQ is generated on an originating node; + +- an RR is generated on a destination node; + +- a global object is created; + +- a global object is deleted; + +- a local task blocked on a remote object is deleted; + +- during system initialization to check for system consistency. + +If the target hardware supports it, the arrival of a +packet at a node may generate an interrupt. Otherwise, the +real-time clock ISR can check for the arrival of a packet. In +any case, the``rtems_multiprocessing_announce`` directive must be called +to announce the arrival of a packet. After exiting the ISR, +control will be passed to the Multiprocessing Server to process +the packet. The Multiprocessing Server will call the get_packet +entry to obtain a packet buffer and the receive_entry entry to +copy the message into the buffer obtained. + +INITIALIZATION +-------------- + +The INITIALIZATION component of the user-provided +MPCI layer is called as part of the ``rtems_initialize_executive`` +directive to initialize the MPCI layer and associated hardware. +It is invoked immediately after all of the device drivers have +been initialized. This component should be adhere to the +following prototype:.. index:: rtems_mpci_entry + +.. code:: c + + rtems_mpci_entry user_mpci_initialization( + rtems_configuration_table \*configuration + ); + +where configuration is the address of the user’s +Configuration Table. Operations on global objects cannot be +performed until this component is invoked. The INITIALIZATION +component is invoked only once in the life of any system. If +the MPCI layer cannot be successfully initialized, the fatal +error manager should be invoked by this routine. + +One of the primary functions of the MPCI layer is to +provide the executive with packet buffers. The INITIALIZATION +routine must create and initialize a pool of packet buffers. +There must be enough packet buffers so RTEMS can obtain one +whenever needed. + +GET_PACKET +---------- + +The GET_PACKET component of the user-provided MPCI +layer is called when RTEMS must obtain a packet buffer to send +or broadcast a message. This component should be adhere to the +following prototype: +.. code:: c + + rtems_mpci_entry user_mpci_get_packet( + rtems_packet_prefix \**packet + ); + +where packet is the address of a pointer to a packet. +This routine always succeeds and, upon return, packet will +contain the address of a packet. If for any reason, a packet +cannot be successfully obtained, then the fatal error manager +should be invoked. + +RTEMS has been optimized to avoid the need for +obtaining a packet each time a message is sent or broadcast. +For example, RTEMS sends response messages (RR) back to the +originator in the same packet in which the request message (RQ) +arrived. + +RETURN_PACKET +------------- + +The RETURN_PACKET component of the user-provided MPCI +layer is called when RTEMS needs to release a packet to the free +packet buffer pool. This component should be adhere to the +following prototype: +.. code:: c + + rtems_mpci_entry user_mpci_return_packet( + rtems_packet_prefix \*packet + ); + +where packet is the address of a packet. If the +packet cannot be successfully returned, the fatal error manager +should be invoked. + +RECEIVE_PACKET +-------------- + +The RECEIVE_PACKET component of the user-provided +MPCI layer is called when RTEMS needs to obtain a packet which +has previously arrived. This component should be adhere to the +following prototype: +.. code:: c + + rtems_mpci_entry user_mpci_receive_packet( + rtems_packet_prefix \**packet + ); + +where packet is a pointer to the address of a packet +to place the message from another node. If a message is +available, then packet will contain the address of the message +from another node. If no messages are available, this entry +packet should contain NULL. + +SEND_PACKET +----------- + +The SEND_PACKET component of the user-provided MPCI +layer is called when RTEMS needs to send a packet containing a +message to another node. This component should be adhere to the +following prototype: +.. code:: c + + rtems_mpci_entry user_mpci_send_packet( + uint32_t node, + rtems_packet_prefix \**packet + ); + +where node is the node number of the destination and packet is the +address of a packet which containing a message. If the packet cannot +be successfully sent, the fatal error manager should be invoked. + +If node is set to zero, the packet is to be +broadcasted to all other nodes in the system. Although some +MPCI layers will be built upon hardware which support a +broadcast mechanism, others may be required to generate a copy +of the packet for each node in the system. + +.. COMMENT: XXX packet_prefix structure needs to be defined in this document + +Many MPCI layers use the ``packet_length`` field of the``rtems_packet_prefix`` portion +of the packet to avoid sending unnecessary data. This is especially +useful if the media connecting the nodes is relatively slow. + +The ``to_convert`` field of the ``rtems_packet_prefix`` portion of the +packet indicates how much of the packet in 32-bit units may require conversion +in a heterogeneous system. + +Supporting Heterogeneous Environments +------------------------------------- +.. index:: heterogeneous multiprocessing + +Developing an MPCI layer for a heterogeneous system +requires a thorough understanding of the differences between the +processors which comprise the system. One difficult problem is +the varying data representation schemes used by different +processor types. The most pervasive data representation problem +is the order of the bytes which compose a data entity. +Processors which place the least significant byte at the +smallest address are classified as little endian processors. +Little endian byte-ordering is shown below: + +.. code:: c + + +---------------+----------------+---------------+----------------+ + | | | | | + | Byte 3 | Byte 2 | Byte 1 | Byte 0 | + | | | | | + +---------------+----------------+---------------+----------------+ + +Conversely, processors which place the most +significant byte at the smallest address are classified as big +endian processors. Big endian byte-ordering is shown below: +.. code:: c + + +---------------+----------------+---------------+----------------+ + | | | | | + | Byte 0 | Byte 1 | Byte 2 | Byte 3 | + | | | | | + +---------------+----------------+---------------+----------------+ + +Unfortunately, sharing a data structure between big +endian and little endian processors requires translation into a +common endian format. An application designer typically chooses +the common endian format to minimize conversion overhead. + +Another issue in the design of shared data structures +is the alignment of data structure elements. Alignment is both +processor and compiler implementation dependent. For example, +some processors allow data elements to begin on any address +boundary, while others impose restrictions. Common restrictions +are that data elements must begin on either an even address or +on a long word boundary. Violation of these restrictions may +cause an exception or impose a performance penalty. + +Other issues which commonly impact the design of +shared data structures include the representation of floating +point numbers, bit fields, decimal data, and character strings. +In addition, the representation method for negative integers +could be one’s or two’s complement. These factors combine to +increase the complexity of designing and manipulating data +structures shared between processors. + +RTEMS addressed these issues in the design of the +packets used to communicate between nodes. The RTEMS packet +format is designed to allow the MPCI layer to perform all +necessary conversion without burdening the developer with the +details of the RTEMS packet format. As a result, the MPCI layer +must be aware of the following: + +- All packets must begin on a four byte boundary. + +- Packets are composed of both RTEMS and application data. All RTEMS data + is treated as 32-bit unsigned quantities and is in the first ``to_convert`` + 32-bit quantities of the packet. The ``to_convert`` field is part of the``rtems_packet_prefix`` portion of the packet. + +- The RTEMS data component of the packet must be in native + endian format. Endian conversion may be performed by either the + sending or receiving MPCI layer. + +- RTEMS makes no assumptions regarding the application + data component of the packet. + +Operations +========== + +Announcing a Packet +------------------- + +The ``rtems_multiprocessing_announce`` directive is called by +the MPCI layer to inform RTEMS that a packet has arrived from +another node. This directive can be called from an interrupt +service routine or from within a polling routine. + +Directives +========== + +This section details the additional directives +required to support RTEMS in a multiprocessor configuration. A +subsection is dedicated to each of this manager’s directives and +describes the calling sequence, related constants, usage, and +status codes. + +MULTIPROCESSING_ANNOUNCE - Announce the arrival of a packet +----------------------------------------------------------- +.. index:: announce arrival of package + +**CALLING SEQUENCE:** + +.. index:: rtems_multiprocessing_announce + +.. code:: c + + void rtems_multiprocessing_announce( void ); + +**DIRECTIVE STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive informs RTEMS that a multiprocessing +communications packet has arrived from another node. This +directive is called by the user-provided MPCI, and is only used +in multiprocessor configurations. + +**NOTES:** + +This directive is typically called from an ISR. + +This directive will almost certainly cause the +calling task to be preempted. + +This directive does not generate activity on remote nodes. + +.. COMMENT: COPYRIGHT (c) 2014. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Symmetric Multiprocessing Services +################################## + +Introduction +============ + +The Symmetric Multiprocessing (SMP) support of the RTEMS 4.10.99.0 is +available on + +- ARM, + +- PowerPC, and + +- SPARC. + +It must be explicitly enabled via the ``--enable-smp`` configure command +line option. To enable SMP in the application configuration see `Enable SMP Support for Applications`_. The default +scheduler for SMP applications supports up to 32 processors and is a global +fixed priority scheduler, see also `Configuring Clustered Schedulers`_. For example applications see:file:`testsuites/smptests`. + +*WARNING: The SMP support in RTEMS is work in progress. Before you +start using this RTEMS version for SMP ask on the RTEMS mailing list.* + +This chapter describes the services related to Symmetric Multiprocessing +provided by RTEMS. + +The application level services currently provided are: + +- ``rtems_get_processor_count`` - Get processor count + +- ``rtems_get_current_processor`` - Get current processor index + +- ``rtems_scheduler_ident`` - Get ID of a scheduler + +- ``rtems_scheduler_get_processor_set`` - Get processor set of a scheduler + +- ``rtems_task_get_scheduler`` - Get scheduler of a task + +- ``rtems_task_set_scheduler`` - Set scheduler of a task + +- ``rtems_task_get_affinity`` - Get task processor affinity + +- ``rtems_task_set_affinity`` - Set task processor affinity + +Background +========== + +Uniprocessor versus SMP Parallelism +----------------------------------- + +Uniprocessor systems have long been used in embedded systems. In this hardware +model, there are some system execution characteristics which have long been +taken for granted: + +- one task executes at a time + +- hardware events result in interrupts + +There is no true parallelism. Even when interrupts appear to occur +at the same time, they are processed in largely a serial fashion. +This is true even when the interupt service routines are allowed to +nest. From a tasking viewpoint, it is the responsibility of the real-time +operatimg system to simulate parallelism by switching between tasks. +These task switches occur in response to hardware interrupt events and explicit +application events such as blocking for a resource or delaying. + +With symmetric multiprocessing, the presence of multiple processors +allows for true concurrency and provides for cost-effective performance +improvements. Uniprocessors tend to increase performance by increasing +clock speed and complexity. This tends to lead to hot, power hungry +microprocessors which are poorly suited for many embedded applications. + +The true concurrency is in sharp contrast to the single task and +interrupt model of uniprocessor systems. This results in a fundamental +change to uniprocessor system characteristics listed above. Developers +are faced with a different set of characteristics which, in turn, break +some existing assumptions and result in new challenges. In an SMP system +with N processors, these are the new execution characteristics. + +- N tasks execute in parallel + +- hardware events result in interrupts + +There is true parallelism with a task executing on each processor and +the possibility of interrupts occurring on each processor. Thus in contrast +to their being one task and one interrupt to consider on a uniprocessor, +there are N tasks and potentially N simultaneous interrupts to consider +on an SMP system. + +This increase in hardware complexity and presence of true parallelism +results in the application developer needing to be even more cautious +about mutual exclusion and shared data access than in a uniprocessor +embedded system. Race conditions that never or rarely happened when an +application executed on a uniprocessor system, become much more likely +due to multiple threads executing in parallel. On a uniprocessor system, +these race conditions would only happen when a task switch occurred at +just the wrong moment. Now there are N-1 tasks executing in parallel +all the time and this results in many more opportunities for small +windows in critical sections to be hit. + +Task Affinity +------------- +.. index:: task affinity +.. index:: thread affinity + +RTEMS provides services to manipulate the affinity of a task. Affinity +is used to specify the subset of processors in an SMP system on which +a particular task can execute. + +By default, tasks have an affinity which allows them to execute on any +available processor. + +Task affinity is a possible feature to be supported by SMP-aware +schedulers. However, only a subset of the available schedulers support +affinity. Although the behavior is scheduler specific, if the scheduler +does not support affinity, it is likely to ignore all attempts to set +affinity. + +The scheduler with support for arbitary processor affinities uses a proof of +concept implementation. See https://devel.rtems.org/ticket/2510. + +Task Migration +-------------- +.. index:: task migration +.. index:: thread migration + +With more than one processor in the system tasks can migrate from one processor +to another. There are three reasons why tasks migrate in RTEMS. + +- The scheduler changes explicitly via ``rtems_task_set_scheduler()`` or + similar directives. + +- The task resumes execution after a blocking operation. On a priority + based scheduler it will evict the lowest priority task currently assigned to a + processor in the processor set managed by the scheduler instance. + +- The task moves temporarily to another scheduler instance due to locking + protocols like *Migratory Priority Inheritance* or the*Multiprocessor Resource Sharing Protocol*. + +Task migration should be avoided so that the working set of a task can stay on +the most local cache level. + +The current implementation of task migration in RTEMS has some implications +with respect to the interrupt latency. It is crucial to preserve the system +invariant that a task can execute on at most one processor in the system at a +time. This is accomplished with a boolean indicator in the task context. The +processor architecture specific low-level task context switch code will mark +that a task context is no longer executing and waits that the heir context +stopped execution before it restores the heir context and resumes execution of +the heir task. So there is one point in time in which a processor is without a +task. This is essential to avoid cyclic dependencies in case multiple tasks +migrate at once. Otherwise some supervising entity is necessary to prevent +life-locks. Such a global supervisor would lead to scalability problems so +this approach is not used. Currently the thread dispatch is performed with +interrupts disabled. So in case the heir task is currently executing on +another processor then this prolongs the time of disabled interrupts since one +processor has to wait for another processor to make progress. + +It is difficult to avoid this issue with the interrupt latency since interrupts +normally store the context of the interrupted task on its stack. In case a +task is marked as not executing we must not use its task stack to store such an +interrupt context. We cannot use the heir stack before it stopped execution on +another processor. So if we enable interrupts during this transition we have +to provide an alternative task independent stack for this time frame. This +issue needs further investigation. + +Clustered Scheduling +-------------------- + +We have clustered scheduling in case the set of processors of a system is +partitioned into non-empty pairwise-disjoint subsets. These subsets are called +clusters. Clusters with a cardinality of one are partitions. Each cluster is +owned by exactly one scheduler instance. + +Clustered scheduling helps to control the worst-case latencies in +multi-processor systems, see *Brandenburg, Björn B.: Scheduling and +Locking in Multiprocessor Real-Time Operating Systems. PhD thesis, 2011.http://www.cs.unc.edu/~bbb/diss/brandenburg-diss.pdf*. The goal is to +reduce the amount of shared state in the system and thus prevention of lock +contention. Modern multi-processor systems tend to have several layers of data +and instruction caches. With clustered scheduling it is possible to honour the +cache topology of a system and thus avoid expensive cache synchronization +traffic. It is easy to implement. The problem is to provide synchronization +primitives for inter-cluster synchronization (more than one cluster is involved +in the synchronization process). In RTEMS there are currently four means +available + +- events, + +- message queues, + +- semaphores using the `Priority Inheritance`_ + protocol (priority boosting), and + +- semaphores using the `Multiprocessor Resource Sharing Protocol`_ (MrsP). + +The clustered scheduling approach enables separation of functions with +real-time requirements and functions that profit from fairness and high +throughput provided the scheduler instances are fully decoupled and adequate +inter-cluster synchronization primitives are used. This is work in progress. + +For the configuration of clustered schedulers see `Configuring Clustered Schedulers`_. + +To set the scheduler of a task see `SCHEDULER_IDENT - Get ID of a scheduler`_ +and `TASK_SET_SCHEDULER - Set scheduler of a task`_. + +Task Priority Queues +-------------------- + +Due to the support for clustered scheduling the task priority queues need +special attention. It makes no sense to compare the priority values of two +different scheduler instances. Thus, it is not possible to simply use one +plain priority queue for tasks of different scheduler instances. + +One solution to this problem is to use two levels of queues. The top level +queue provides FIFO ordering and contains priority queues. Each priority queue +is associated with a scheduler instance and contains only tasks of this +scheduler instance. Tasks are enqueued in the priority queue corresponding to +their scheduler instance. In case this priority queue was empty, then it is +appended to the FIFO. To dequeue a task the highest priority task of the first +priority queue in the FIFO is selected. Then the first priority queue is +removed from the FIFO. In case the previously first priority queue is not +empty, then it is appended to the FIFO. So there is FIFO fairness with respect +to the highest priority task of each scheduler instances. See also *Brandenburg, Björn B.: A fully preemptive multiprocessor semaphore protocol for +latency-sensitive real-time applications. In Proceedings of the 25th Euromicro +Conference on Real-Time Systems (ECRTS 2013), pages 292–302, 2013.http://www.mpi-sws.org/~bbb/papers/pdf/ecrts13b.pdf*. + +Such a two level queue may need a considerable amount of memory if fast enqueue +and dequeue operations are desired (depends on the scheduler instance count). +To mitigate this problem an approch of the FreeBSD kernel was implemented in +RTEMS. We have the invariant that a task can be enqueued on at most one task +queue. Thus, we need only as many queues as we have tasks. Each task is +equipped with spare task queue which it can give to an object on demand. The +task queue uses a dedicated memory space independent of the other memory used +for the task itself. In case a task needs to block, then there are two options + +- the object already has task queue, then the task enqueues itself to this + already present queue and the spare task queue of the task is added to a list + of free queues for this object, or + +- otherwise, then the queue of the task is given to the object and the task + enqueues itself to this queue. + +In case the task is dequeued, then there are two options + +- the task is the last task on the queue, then it removes this queue from + the object and reclaims it for its own purpose, or + +- otherwise, then the task removes one queue from the free list of the + object and reclaims it for its own purpose. + +Since there are usually more objects than tasks, this actually reduces the +memory demands. In addition the objects contain only a pointer to the task +queue structure. This helps to hide implementation details and makes it +possible to use self-contained synchronization objects in Newlib and GCC (C++ +and OpenMP run-time support). + +Scheduler Helping Protocol +-------------------------- + +The scheduler provides a helping protocol to support locking protocols like*Migratory Priority Inheritance* or the *Multiprocessor Resource +Sharing Protocol*. Each ready task can use at least one scheduler node at a +time to gain access to a processor. Each scheduler node has an owner, a user +and an optional idle task. The owner of a scheduler node is determined a task +creation and never changes during the life time of a scheduler node. The user +of a scheduler node may change due to the scheduler helping protocol. A +scheduler node is in one of the four scheduler help states: + +:dfn:`help yourself` + This scheduler node is solely used by the owner task. This task owns no + resources using a helping protocol and thus does not take part in the scheduler + helping protocol. No help will be provided for other tasks. + +:dfn:`help active owner` + This scheduler node is owned by a task actively owning a resource and can be + used to help out tasks. + In case this scheduler node changes its state from ready to scheduled and the + task executes using another node, then an idle task will be provided as a user + of this node to temporarily execute on behalf of the owner task. Thus lower + priority tasks are denied access to the processors of this scheduler instance. + In case a task actively owning a resource performs a blocking operation, then + an idle task will be used also in case this node is in the scheduled state. + +:dfn:`help active rival` + This scheduler node is owned by a task actively obtaining a resource currently + owned by another task and can be used to help out tasks. + The task owning this node is ready and will give away its processor in case the + task owning the resource asks for help. + +:dfn:`help passive` + This scheduler node is owned by a task obtaining a resource currently owned by + another task and can be used to help out tasks. + The task owning this node is blocked. + +The following scheduler operations return a task in need for help + +- unblock, + +- change priority, + +- yield, and + +- ask for help. + +A task in need for help is a task that encounters a scheduler state change from +scheduled to ready (this is a pre-emption by a higher priority task) or a task +that cannot be scheduled in an unblock operation. Such a task can ask tasks +which depend on resources owned by this task for help. + +In case it is not possible to schedule a task in need for help, then the +scheduler nodes available for the task will be placed into the set of ready +scheduler nodes of the corresponding scheduler instances. Once a state change +from ready to scheduled happens for one of scheduler nodes it will be used to +schedule the task in need for help. + +The ask for help scheduler operation is used to help tasks in need for help +returned by the operations mentioned above. This operation is also used in +case the root of a resource sub-tree owned by a task changes. + +The run-time of the ask for help procedures depend on the size of the resource +tree of the task needing help and other resource trees in case tasks in need +for help are produced during this operation. Thus the worst-case latency in +the system depends on the maximum resource tree size of the application. + +Critical Section Techniques and SMP +----------------------------------- + +As discussed earlier, SMP systems have opportunities for true parallelism +which was not possible on uniprocessor systems. Consequently, multiple +techniques that provided adequate critical sections on uniprocessor +systems are unsafe on SMP systems. In this section, some of these +unsafe techniques will be discussed. + +In general, applications must use proper operating system provided mutual +exclusion mechanisms to ensure correct behavior. This primarily means +the use of binary semaphores or mutexes to implement critical sections. + +Disable Interrupts and Interrupt Locks +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A low overhead means to ensure mutual exclusion in uni-processor configurations +is to disable interrupts around a critical section. This is commonly used in +device driver code and throughout the operating system core. On SMP +configurations, however, disabling the interrupts on one processor has no +effect on other processors. So, this is insufficient to ensure system wide +mutual exclusion. The macros + +- ``rtems_interrupt_disable()``, + +- ``rtems_interrupt_enable()``, and + +- ``rtems_interrupt_flush()`` + +are disabled on SMP configurations and its use will lead to compiler warnings +and linker errors. In the unlikely case that interrupts must be disabled on +the current processor, then the + +- ``rtems_interrupt_local_disable()``, and + +- ``rtems_interrupt_local_enable()`` + +macros are now available in all configurations. + +Since disabling of interrupts is not enough to ensure system wide mutual +exclusion on SMP, a new low-level synchronization primitive was added - the +interrupt locks. They are a simple API layer on top of the SMP locks used for +low-level synchronization in the operating system core. Currently they are +implemented as a ticket lock. On uni-processor configurations they degenerate +to simple interrupt disable/enable sequences. It is disallowed to acquire a +single interrupt lock in a nested way. This will result in an infinite loop +with interrupts disabled. While converting legacy code to interrupt locks care +must be taken to avoid this situation. +.. code:: c + + void legacy_code_with_interrupt_disable_enable( void ) + { + rtems_interrupt_level level; + rtems_interrupt_disable( level ); + /* Some critical stuff \*/ + rtems_interrupt_enable( level ); + } + RTEMS_INTERRUPT_LOCK_DEFINE( static, lock, "Name" ) + void smp_ready_code_with_interrupt_lock( void ) + { + rtems_interrupt_lock_context lock_context; + rtems_interrupt_lock_acquire( &lock, &lock_context ); + /* Some critical stuff \*/ + rtems_interrupt_lock_release( &lock, &lock_context ); + } + +The ``rtems_interrupt_lock`` structure is empty on uni-processor +configurations. Empty structures have a different size in C +(implementation-defined, zero in case of GCC) and C++ (implementation-defined +non-zero value, one in case of GCC). Thus the``RTEMS_INTERRUPT_LOCK_DECLARE()``, ``RTEMS_INTERRUPT_LOCK_DEFINE()``,``RTEMS_INTERRUPT_LOCK_MEMBER()``, and``RTEMS_INTERRUPT_LOCK_REFERENCE()`` macros are provided to ensure ABI +compatibility. + +Highest Priority Task Assumption +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +On a uniprocessor system, it is safe to assume that when the highest +priority task in an application executes, it will execute without being +preempted until it voluntarily blocks. Interrupts may occur while it is +executing, but there will be no context switch to another task unless +the highest priority task voluntarily initiates it. + +Given the assumption that no other tasks will have their execution +interleaved with the highest priority task, it is possible for this +task to be constructed such that it does not need to acquire a binary +semaphore or mutex for protected access to shared data. + +In an SMP system, it cannot be assumed there will never be a single task +executing. It should be assumed that every processor is executing another +application task. Further, those tasks will be ones which would not have +been executed in a uniprocessor configuration and should be assumed to +have data synchronization conflicts with what was formerly the highest +priority task which executed without conflict. + +Disable Preemption +~~~~~~~~~~~~~~~~~~ + +On a uniprocessor system, disabling preemption in a task is very similar +to making the highest priority task assumption. While preemption is +disabled, no task context switches will occur unless the task initiates +them voluntarily. And, just as with the highest priority task assumption, +there are N-1 processors also running tasks. Thus the assumption that no +other tasks will run while the task has preemption disabled is violated. + +Task Unique Data and SMP +------------------------ + +Per task variables are a service commonly provided by real-time operating +systems for application use. They work by allowing the application +to specify a location in memory (typically a ``void *``) which is +logically added to the context of a task. On each task switch, the +location in memory is stored and each task can have a unique value in +the same memory location. This memory location is directly accessed as a +variable in a program. + +This works well in a uniprocessor environment because there is one task +executing and one memory location containing a task-specific value. But +it is fundamentally broken on an SMP system because there are always N +tasks executing. With only one location in memory, N-1 tasks will not +have the correct value. + +This paradigm for providing task unique data values is fundamentally +broken on SMP systems. + +Classic API Per Task Variables +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The Classic API provides three directives to support per task variables. These are: + +- ``rtems_task_variable_add`` - Associate per task variable + +- ``rtems_task_variable_get`` - Obtain value of a a per task variable + +- ``rtems_task_variable_delete`` - Remove per task variable + +As task variables are unsafe for use on SMP systems, the use of these services +must be eliminated in all software that is to be used in an SMP environment. +The task variables API is disabled on SMP. Its use will lead to compile-time +and link-time errors. It is recommended that the application developer consider +the use of POSIX Keys or Thread Local Storage (TLS). POSIX Keys are available +in all RTEMS configurations. For the availablity of TLS on a particular +architecture please consult the *RTEMS CPU Architecture Supplement*. + +The only remaining user of task variables in the RTEMS code base is the Ada +support. So basically Ada is not available on RTEMS SMP. + +OpenMP +------ + +OpenMP support for RTEMS is available via the GCC provided libgomp. There is +libgomp support for RTEMS in the POSIX configuration of libgomp since GCC 4.9 +(requires a Newlib snapshot after 2015-03-12). In GCC 6.1 or later (requires a +Newlib snapshot after 2015-07-30 for provided self-contained +synchronization objects) there is a specialized libgomp configuration for RTEMS +which offers a significantly better performance compared to the POSIX +configuration of libgomp. In addition application configurable thread pools +for each scheduler instance are available in GCC 6.1 or later. + +The run-time configuration of libgomp is done via environment variables +documented in the `libgomp +manual `_. The environment variables are evaluated in a constructor function +which executes in the context of the first initialization task before the +actual initialization task function is called (just like a global C++ +constructor). To set application specific values, a higher priority +constructor function must be used to set up the environment variables. +.. code:: c + + #include + void __attribute__((constructor(1000))) config_libgomp( void ) + { + setenv( "OMP_DISPLAY_ENV", "VERBOSE", 1 ); + setenv( "GOMP_SPINCOUNT", "30000", 1 ); + setenv( "GOMP_RTEMS_THREAD_POOLS", "1$2@SCHD", 1 ); + } + +The environment variable ``GOMP_RTEMS_THREAD_POOLS`` is RTEMS-specific. It +determines the thread pools for each scheduler instance. The format for``GOMP_RTEMS_THREAD_POOLS`` is a list of optional``[$]@`` configurations +separated by ``:`` where: + +- ```` is the thread pool count for this scheduler + instance. + +- ``$`` is an optional priority for the worker threads of a + thread pool according to ``pthread_setschedparam``. In case a priority + value is omitted, then a worker thread will inherit the priority of the OpenMP + master thread that created it. The priority of the worker thread is not + changed by libgomp after creation, even if a new OpenMP master thread using the + worker has a different priority. + +- ``@`` is the scheduler instance name according to the + RTEMS application configuration. + +In case no thread pool configuration is specified for a scheduler instance, +then each OpenMP master thread of this scheduler instance will use its own +dynamically allocated thread pool. To limit the worker thread count of the +thread pools, each OpenMP master thread must call ``omp_set_num_threads``. + +Lets suppose we have three scheduler instances ``IO``, ``WRK0``, and``WRK1`` with ``GOMP_RTEMS_THREAD_POOLS`` set to``"1@WRK0:3$4@WRK1"``. Then there are no thread pool restrictions for +scheduler instance ``IO``. In the scheduler instance ``WRK0`` there is +one thread pool available. Since no priority is specified for this scheduler +instance, the worker thread inherits the priority of the OpenMP master thread +that created it. In the scheduler instance ``WRK1`` there are three thread +pools available and their worker threads run at priority four. + +Thread Dispatch Details +----------------------- + +This section gives background information to developers interested in the +interrupt latencies introduced by thread dispatching. A thread dispatch +consists of all work which must be done to stop the currently executing thread +on a processor and hand over this processor to an heir thread. + +On SMP systems, scheduling decisions on one processor must be propagated to +other processors through inter-processor interrupts. So, a thread dispatch +which must be carried out on another processor happens not instantaneous. Thus +several thread dispatch requests might be in the air and it is possible that +some of them may be out of date before the corresponding processor has time to +deal with them. The thread dispatch mechanism uses three per-processor +variables, + +- the executing thread, + +- the heir thread, and + +- an boolean flag indicating if a thread dispatch is necessary or not. + +Updates of the heir thread and the thread dispatch necessary indicator are +synchronized via explicit memory barriers without the use of locks. A thread +can be an heir thread on at most one processor in the system. The thread context +is protected by a TTAS lock embedded in the context to ensure that it is used +on at most one processor at a time. The thread post-switch actions use a +per-processor lock. This implementation turned out to be quite efficient and +no lock contention was observed in the test suite. + +The current implementation of thread dispatching has some implications with +respect to the interrupt latency. It is crucial to preserve the system +invariant that a thread can execute on at most one processor in the system at a +time. This is accomplished with a boolean indicator in the thread context. +The processor architecture specific context switch code will mark that a thread +context is no longer executing and waits that the heir context stopped +execution before it restores the heir context and resumes execution of the heir +thread (the boolean indicator is basically a TTAS lock). So, there is one +point in time in which a processor is without a thread. This is essential to +avoid cyclic dependencies in case multiple threads migrate at once. Otherwise +some supervising entity is necessary to prevent deadlocks. Such a global +supervisor would lead to scalability problems so this approach is not used. +Currently the context switch is performed with interrupts disabled. Thus in +case the heir thread is currently executing on another processor, the time of +disabled interrupts is prolonged since one processor has to wait for another +processor to make progress. + +It is difficult to avoid this issue with the interrupt latency since interrupts +normally store the context of the interrupted thread on its stack. In case a +thread is marked as not executing, we must not use its thread stack to store +such an interrupt context. We cannot use the heir stack before it stopped +execution on another processor. If we enable interrupts during this +transition, then we have to provide an alternative thread independent stack for +interrupts in this time frame. This issue needs further investigation. + +The problematic situation occurs in case we have a thread which executes with +thread dispatching disabled and should execute on another processor (e.g. it is +an heir thread on another processor). In this case the interrupts on this +other processor are disabled until the thread enables thread dispatching and +starts the thread dispatch sequence. The scheduler (an exception is the +scheduler with thread processor affinity support) tries to avoid such a +situation and checks if a new scheduled thread already executes on a processor. +In case the assigned processor differs from the processor on which the thread +already executes and this processor is a member of the processor set managed by +this scheduler instance, it will reassign the processors to keep the already +executing thread in place. Therefore normal scheduler requests will not lead +to such a situation. Explicit thread migration requests, however, can lead to +this situation. Explicit thread migrations may occur due to the scheduler +helping protocol or explicit scheduler instance changes. The situation can +also be provoked by interrupts which suspend and resume threads multiple times +and produce stale asynchronous thread dispatch requests in the system. + +Operations +========== + +Setting Affinity to a Single Processor +-------------------------------------- + +On some embedded applications targeting SMP systems, it may be beneficial to +lock individual tasks to specific processors. In this way, one can designate a +processor for I/O tasks, another for computation, etc.. The following +illustrates the code sequence necessary to assign a task an affinity for +processor with index ``processor_index``. +.. code:: c + + #include + #include + void pin_to_processor(rtems_id task_id, int processor_index) + { + rtems_status_code sc; + cpu_set_t cpuset; + CPU_ZERO(&cpuset); + CPU_SET(processor_index, &cpuset); + sc = rtems_task_set_affinity(task_id, sizeof(cpuset), &cpuset); + assert(sc == RTEMS_SUCCESSFUL); + } + +It is important to note that the ``cpuset`` is not validated until the``rtems_task_set_affinity`` call is made. At that point, +it is validated against the current system configuration. + +Directives +========== + +This section details the symmetric multiprocessing services. A subsection +is dedicated to each of these services and describes the calling sequence, +related constants, usage, and status codes. + +.. COMMENT: rtems_get_processor_count + +GET_PROCESSOR_COUNT - Get processor count +----------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + uint32_t rtems_get_processor_count(void); + +**DIRECTIVE STATUS CODES:** + +The count of processors in the system. + +**DESCRIPTION:** + +On uni-processor configurations a value of one will be returned. + +On SMP configurations this returns the value of a global variable set during +system initialization to indicate the count of utilized processors. The +processor count depends on the physically or virtually available processors and +application configuration. The value will always be less than or equal to the +maximum count of application configured processors. + +**NOTES:** + +None. + +.. COMMENT: rtems_get_current_processor + +GET_CURRENT_PROCESSOR - Get current processor index +--------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + uint32_t rtems_get_current_processor(void); + +**DIRECTIVE STATUS CODES:** + +The index of the current processor. + +**DESCRIPTION:** + +On uni-processor configurations a value of zero will be returned. + +On SMP configurations an architecture specific method is used to obtain the +index of the current processor in the system. The set of processor indices is +the range of integers starting with zero up to the processor count minus one. + +Outside of sections with disabled thread dispatching the current processor +index may change after every instruction since the thread may migrate from one +processor to another. Sections with disabled interrupts are sections with +thread dispatching disabled. + +**NOTES:** + +None. + +.. COMMENT: rtems_scheduler_ident + + +SCHEDULER_IDENT - Get ID of a scheduler +--------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + rtems_status_code rtems_scheduler_ident( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successful operation +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - invalid scheduler name +``RTEMS_UNSATISFIED`` - - a scheduler with this name exists, but +the processor set of this scheduler is empty + +**DESCRIPTION:** + +Identifies a scheduler by its name. The scheduler name is determined by the +scheduler configuration. See `Configuring a System`_. + +**NOTES:** + +None. + +.. COMMENT: rtems_scheduler_get_processor_set + +SCHEDULER_GET_PROCESSOR_SET - Get processor set of a scheduler +-------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + rtems_status_code rtems_scheduler_get_processor_set( + rtems_id scheduler_id, + size_t cpusetsize, + cpu_set_t \*cpuset + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successful operation +``RTEMS_INVALID_ADDRESS`` - ``cpuset`` is NULL +``RTEMS_INVALID_ID`` - invalid scheduler id +``RTEMS_INVALID_NUMBER`` - the affinity set buffer is too small for +set of processors owned by the scheduler + +**DESCRIPTION:** + +Returns the processor set owned by the scheduler in ``cpuset``. A set bit +in the processor set means that this processor is owned by the scheduler and a +cleared bit means the opposite. + +**NOTES:** + +None. + +.. COMMENT: rtems_task_get_scheduler + +TASK_GET_SCHEDULER - Get scheduler of a task +-------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + rtems_status_code rtems_task_get_scheduler( + rtems_id task_id, + rtems_id \*scheduler_id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successful operation +``RTEMS_INVALID_ADDRESS`` - ``scheduler_id`` is NULL +``RTEMS_INVALID_ID`` - invalid task id + +**DESCRIPTION:** + +Returns the scheduler identifier of a task identified by ``task_id`` in``scheduler_id``. + +**NOTES:** + +None. + +.. COMMENT: rtems_task_set_scheduler + + +TASK_SET_SCHEDULER - Set scheduler of a task +-------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + rtems_status_code rtems_task_set_scheduler( + rtems_id task_id, + rtems_id scheduler_id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successful operation +``RTEMS_INVALID_ID`` - invalid task or scheduler id +``RTEMS_INCORRECT_STATE`` - the task is in the wrong state to +perform a scheduler change + +**DESCRIPTION:** + +Sets the scheduler of a task identified by ``task_id`` to the scheduler +identified by ``scheduler_id``. The scheduler of a task is initialized to +the scheduler of the task that created it. + +**NOTES:** + +None. + +**EXAMPLE:** + +.. code:: c + + #include + #include + void task(rtems_task_argument arg); + void example(void) + { + rtems_status_code sc; + rtems_id task_id; + rtems_id scheduler_id; + rtems_name scheduler_name; + scheduler_name = rtems_build_name('W', 'O', 'R', 'K'); + sc = rtems_scheduler_ident(scheduler_name, &scheduler_id); + assert(sc == RTEMS_SUCCESSFUL); + sc = rtems_task_create( + rtems_build_name('T', 'A', 'S', 'K'), + 1, + RTEMS_MINIMUM_STACK_SIZE, + RTEMS_DEFAULT_MODES, + RTEMS_DEFAULT_ATTRIBUTES, + &task_id + ); + assert(sc == RTEMS_SUCCESSFUL); + sc = rtems_task_set_scheduler(task_id, scheduler_id); + assert(sc == RTEMS_SUCCESSFUL); + sc = rtems_task_start(task_id, task, 0); + assert(sc == RTEMS_SUCCESSFUL); + } + +.. COMMENT: rtems_task_get_affinity + +TASK_GET_AFFINITY - Get task processor affinity +----------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + rtems_status_code rtems_task_get_affinity( + rtems_id id, + size_t cpusetsize, + cpu_set_t \*cpuset + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successful operation +``RTEMS_INVALID_ADDRESS`` - ``cpuset`` is NULL +``RTEMS_INVALID_ID`` - invalid task id +``RTEMS_INVALID_NUMBER`` - the affinity set buffer is too small for +the current processor affinity set of the task + +**DESCRIPTION:** + +Returns the current processor affinity set of the task in ``cpuset``. A set +bit in the affinity set means that the task can execute on this processor and a +cleared bit means the opposite. + +**NOTES:** + +None. + +.. COMMENT: rtems_task_set_affinity + +TASK_SET_AFFINITY - Set task processor affinity +----------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + rtems_status_code rtems_task_set_affinity( + rtems_id id, + size_t cpusetsize, + const cpu_set_t \*cpuset + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - successful operation +``RTEMS_INVALID_ADDRESS`` - ``cpuset`` is NULL +``RTEMS_INVALID_ID`` - invalid task id +``RTEMS_INVALID_NUMBER`` - invalid processor affinity set + +**DESCRIPTION:** + +Sets the processor affinity set for the task specified by ``cpuset``. A set +bit in the affinity set means that the task can execute on this processor and a +cleared bit means the opposite. + +**NOTES:** + +This function will not change the scheduler of the task. The intersection of +the processor affinity set and the set of processors owned by the scheduler of +the task must be non-empty. It is not an error if the processor affinity set +contains processors that are not part of the set of processors owned by the +scheduler instance of the task. A task will simply not run under normal +circumstances on these processors since the scheduler ignores them. Some +locking protocols may temporarily use processors that are not included in the +processor affinity set of the task. It is also not an error if the processor +affinity set contains processors that are not part of the system. + +.. COMMENT: COPYRIGHT (c) 2011,2015 + +.. COMMENT: Aeroflex Gaisler AB + +.. COMMENT: All rights reserved. + +PCI Library +########### + +.. index:: libpci + +Introduction +============ + +The Peripheral Component Interconnect (PCI) bus is a very common computer +bus architecture that is found in almost every PC today. The PCI bus is +normally located at the motherboard where some PCI devices are soldered +directly onto the PCB and expansion slots allows the user to add custom +devices easily. There is a wide range of PCI hardware available implementing +all sorts of interfaces and functions. + +This section describes the PCI Library available in RTEMS used to access the +PCI bus in a portable way across computer architectures supported by RTEMS. + +The PCI Library aims to be compatible with PCI 2.3 with a couple of +limitations, for example there is no support for hot-plugging, 64-bit +memory space and cardbus bridges. + +In order to support different architectures and with small foot-print embedded +systems in mind the PCI Library offers four different configuration options +listed below. It is selected during compile time by defining the appropriate +macros in confdefs.h. It is also possible to enable PCI_LIB_NONE (No +Configuration) which can be used for debuging PCI access functions. + +- Auto Configuration (do Plug & Play) + +- Read Configuration (read BIOS or boot loader configuration) + +- Static Configuration (write user defined configuration) + +- Peripheral Configuration (no access to cfg-space) + +Background +========== + +The PCI bus is constructed in a way where on-board devices and devices +in expansion slots can be automatically found (probed) and configured +using Plug & Play completely implemented in software. The bus is set up once +during boot up. The Plug & Play information can be read and written from +PCI configuration space. A PCI device is identified in configuration space by +a unique bus, slot and function number. Each PCI slot can have up to 8 +functions and interface to another PCI sub-bus by implementing a PCI-to-PCI +bridge according to the PCI Bridge Architecture specification. + +Using the unique \[bus:slot:func] any device can be configured regardless of how +PCI is currently set up as long as all PCI buses are enumerated correctly. The +enumeration is done during probing, all bridges are given a bus number in +order for the bridges to respond to accesses from both directions. The PCI +library can assign address ranges to which a PCI device should respond using +Plug & Play technique or a static user defined configuration. After the +configuration has been performed the PCI device drivers can find devices by +the read-only PCI Class type, Vendor ID and Device ID information found in +configuration space for each device. + +In some systems there is a boot loader or BIOS which have already configured +all PCI devices, but on embedded targets it is quite common that there is no +BIOS or boot loader, thus RTEMS must configure the PCI bus. Only the PCI host +may do configuration space access, the host driver or BSP is responsible to +translate the \[bus:slot:func] into a valid PCI configuration space access. + +If the target is not a host, but a peripheral, configuration space can not be +accessed, the peripheral is set up by the host during start up. In complex +embedded PCI systems the peripheral may need to access other PCI boards than +the host. In such systems a custom (static) configuration of both the host +and peripheral may be a convenient solution. + +The PCI bus defines four interrupt signals INTA#..INTD#. The interrupt signals +must be mapped into a system interrupt/vector, it is up to the BSP or host +driver to know the mapping, however the BIOS or boot loader may use the +8-bit read/write "Interrupt Line" register to pass the knowledge along to the +OS. + +The PCI standard defines and recommends that the backplane route the interupt +lines in a systematic way, however in standard there is no such requirement. +The PCI Auto Configuration Library implements the recommended way of routing +which is very common but it is also supported to some extent to override the +interrupt routing from the BSP or Host Bridge driver using the configuration +structure. + +Software Components +------------------- + +The PCI library is located in cpukit/libpci, it consists of different parts: + +- PCI Host bridge driver interface + +- Configuration routines + +- Access (Configuration, I/O and Memory space) routines + +- Interrupt routines (implemented by BSP) + +- Print routines + +- Static/peripheral configuration creation + +- PCI shell command + +PCI Configuration +----------------- + +During start up the PCI bus must be configured in order for host and +peripherals to access one another using Memory or I/O accesses and that +interrupts are properly handled. Three different spaces are defined and +mapped separately: + +# I/O space (IO) + +# non-prefetchable Memory space (MEMIO) + +# prefetchable Memory space (MEM) + +Regions of the same type (I/O or Memory) may not overlap which is guaranteed +by the software. MEM regions may be mapped into MEMIO regions, but MEMIO +regions can not be mapped into MEM, for that could lead to prefetching of +registers. The interrupt pin which a board is driving can be read out from +PCI configuration space, however it is up to software to know how interrupt +signals are routed between PCI-to-PCI bridges and how PCI INT[A..D]# pins are +mapped to system IRQ. In systems where previous software (boot loader or BIOS) +has already set up this the configuration is overwritten or simply read out. + +In order to support different configuration methods the following configuration +libraries are selectable by the user: + +- Auto Configuration (run Plug & Play software) + +- Read Configuration (relies on a boot loader or BIOS) + +- Static Configuration (write user defined setup, no Plug & Play) + +- Peripheral Configuration (user defined setup, no access to + configuration space) + +A host driver can be made to support all three configuration methods, or any +combination. It may be defined by the BSP which approach is used. + +The configuration software is called from the PCI driver (pci_config_init()). + +Regardless of configuration method a PCI device tree is created in RAM during +initialization, the tree can be accessed to find devices and resources without +accessing configuration space later on. The user is responsible to create the +device tree at compile time when using the static/peripheral method. + +RTEMS Configuration selection +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The active configuration method can be selected at compile time in the same +way as other project parameters by including rtems/confdefs.h and setting + +- CONFIGURE_INIT + +- RTEMS_PCI_CONFIG_LIB + +- CONFIGURE_PCI_LIB = PCI_LIB_(AUTO,STATIC,READ,PERIPHERAL) + +See the RTEMS configuration section how to setup the PCI library. + +Auto Configuration +~~~~~~~~~~~~~~~~~~ + +The auto configuration software enumerates PCI buses and initializes all PCI +devices found using Plug & Play. The auto configuration software requires +that a configuration setup has been registered by the driver or BSP in order +to setup the I/O and Memory regions at the correct address ranges. PCI +interrupt pins can optionally be routed over PCI-to-PCI bridges and mapped +to a system interrupt number. BAR resources are sorted by size and required +alignment, unused "dead" space may be created when PCI bridges are present +due to the PCI bridge window size does not equal the alignment. To cope with +that resources are reordered to fit smaller BARs into the dead space to minimize +the PCI space required. If a BAR or ROM register can not be allocated a PCI +address region (due to too few resources available) the register will be given +the value of pci_invalid_address which defaults to 0. + +The auto configuration routines support: + +- PCI 2.3 + +- Little and big endian PCI bus + +- one I/O 16 or 32-bit range (IO) + +- memory space (MEMIO) + +- prefetchable memory space (MEM), if not present MEM will be mapped into + MEMIO + +- multiple PCI buses - PCI-to-PCI bridges + +- standard BARs, PCI-to-PCI bridge BARs, ROM BARs + +- Interrupt routing over bridges + +- Interrupt pin to system interrupt mapping + +Not supported: + +- hot-pluggable devices + +- Cardbus bridges + +- 64-bit memory space + +- 16-bit and 32-bit I/O address ranges at the same time + +In PCI 2.3 there may exist I/O BARs that must be located at the low 64kBytes +address range, in order to support this the host driver or BSP must make sure +that I/O addresses region is within this region. + +Read Configuration +~~~~~~~~~~~~~~~~~~ + +When a BIOS or boot loader already has setup the PCI bus the configuration can +be read directly from the PCI resource registers and buses are already +enumerated, this is a much simpler approach than configuring PCI ourselves. The +PCI device tree is automatically created based on the current configuration and +devices present. After initialization is done there is no difference between +the auto or read configuration approaches. + +Static Configuration +~~~~~~~~~~~~~~~~~~~~ + +To support custom configurations and small-footprint PCI systems, the user may +provide the PCI device tree which contains the current configuration. The +PCI buses are enumerated and all resources are written to PCI devices during +initialization. When this approach is selected PCI boards must be located at +the same slots every time and devices can not be removed or added, Plug & Play +is not performed. Boards of the same type may of course be exchanged. + +The user can create a configuration by calling pci_cfg_print() on a running +system that has had PCI setup by the auto or read configuration routines, it +can be called from the PCI shell command. The user must provide the PCI device +tree named pci_hb. + +Peripheral Configuration +~~~~~~~~~~~~~~~~~~~~~~~~ + +On systems where a peripheral PCI device needs to access other PCI devices than +the host the peripheral configuration approach may be handy. Most PCI devices +answers on the PCI host’s requests and start DMA accesses into the Hosts memory, +however in some complex systems PCI devices may want to access other devices +on the same bus or at another PCI bus. + +A PCI peripheral is not allowed to do PCI configuration cycles, which +means that it must either rely on the host to give it the addresses it +needs, or that the addresses are predefined. + +This configuration approach is very similar to the static option, however the +configuration is never written to PCI bus, instead it is only used for drivers +to find PCI devices and resources using the same PCI API as for the host + +PCI Access +---------- + +The PCI access routines are low-level routines provided for drivers, +configuration software, etc. in order to access different regions in a way +not dependent upon the host driver, BSP or platform. + +- PCI configuration space + +- PCI I/O space + +- Registers over PCI memory space + +- Translate PCI address into CPU accessible address and vice versa + +By using the access routines drivers can be made portable over different +architectures. The access routines take the architecture endianness into +consideration and let the host driver or BSP implement I/O space and +configuration space access. + +Some non-standard hardware may also define the PCI bus big-endian, for example +the LEON2 AT697 PCI host bridge and some LEON3 systems may be configured that +way. It is up to the BSP to set the appropriate PCI endianness on compile time +(BSP_PCI_BIG_ENDIAN) in order for inline macros to be correctly defined. +Another possibility is to use the function pointers defined by the access +layer to implement drivers that support "run-time endianness detection". + +Configuration space +~~~~~~~~~~~~~~~~~~~ + +Configuration space is accessed using the routines listed below. The +pci_dev_t type is used to specify a specific PCI bus, device and function. It +is up to the host driver or BSP to create a valid access to the requested +PCI slot. Requests made to slots that are not supported by hardware should +result in PCISTS_MSTABRT and/or data must be ignored (writes) or 0xffffffff +is always returned (reads). +.. code:: c + + /* Configuration Space Access Read Routines \*/ + extern int pci_cfg_r8(pci_dev_t dev, int ofs, uint8_t \*data); + extern int pci_cfg_r16(pci_dev_t dev, int ofs, uint16_t \*data); + extern int pci_cfg_r32(pci_dev_t dev, int ofs, uint32_t \*data); + /* Configuration Space Access Write Routines \*/ + extern int pci_cfg_w8(pci_dev_t dev, int ofs, uint8_t data); + extern int pci_cfg_w16(pci_dev_t dev, int ofs, uint16_t data); + extern int pci_cfg_w32(pci_dev_t dev, int ofs, uint32_t data); + +I/O space +~~~~~~~~~ + +The BSP or driver provide special routines in order to access I/O space. Some +architectures have a special instruction accessing I/O space, others have it +mapped into a "PCI I/O window" in the standard address space accessed by the +CPU. The window size may vary and must be taken into consideration by the +host driver. The below routines must be used to access I/O space. The address +given to the functions is not the PCI I/O addresses, the caller must have +translated PCI I/O addresses (available in the PCI BARs) into a BSP or host +driver custom address, see `Access functions`_ for how +addresses are translated. + +.. code:: c + + /* Read a register over PCI I/O Space \*/ + extern uint8_t pci_io_r8(uint32_t adr); + extern uint16_t pci_io_r16(uint32_t adr); + extern uint32_t pci_io_r32(uint32_t adr); + /* Write a register over PCI I/O Space \*/ + extern void pci_io_w8(uint32_t adr, uint8_t data); + extern void pci_io_w16(uint32_t adr, uint16_t data); + extern void pci_io_w32(uint32_t adr, uint32_t data); + +Registers over Memory space +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +PCI host bridge hardware normally swap data accesses into the endianness of the +host architecture in order to lower the load of the CPU, peripherals can do DMA +without swapping. However, the host controller can not separate a standard +memory access from a memory access to a register, registers may be mapped into +memory space. This leads to register content being swapped, which must be +swapped back. The below routines makes it possible to access registers over PCI +memory space in a portable way on different architectures, the BSP or +architecture must provide necessary functions in order to implement this. +.. code:: c + + static inline uint16_t pci_ld_le16(volatile uint16_t \*addr); + static inline void pci_st_le16(volatile uint16_t \*addr, uint16_t val); + static inline uint32_t pci_ld_le32(volatile uint32_t \*addr); + static inline void pci_st_le32(volatile uint32_t \*addr, uint32_t val); + static inline uint16_t pci_ld_be16(volatile uint16_t \*addr); + static inline void pci_st_be16(volatile uint16_t \*addr, uint16_t val); + static inline uint32_t pci_ld_be32(volatile uint32_t \*addr); + static inline void pci_st_be32(volatile uint32_t \*addr, uint32_t val); + +In order to support non-standard big-endian PCI bus the above pci_* functions +is required, pci_ld_le16 != ld_le16 on big endian PCI buses. + +Access functions +~~~~~~~~~~~~~~~~ + +The PCI Access Library can provide device drivers with function pointers +executing the above Configuration, I/O and Memory space accesses. The +functions have the same arguments and return values as the above +functions. + +The pci_access_func() function defined below can be used to get a function +pointer of a specific access type. +.. code:: c + + /* Get Read/Write function for accessing a register over PCI Memory Space + * (non-inline functions). + * + * Arguments + * wr 0(Read), 1(Write) + * size 1(Byte), 2(Word), 4(Double Word) + * func Where function pointer will be stored + * endian PCI_LITTLE_ENDIAN or PCI_BIG_ENDIAN + * type 1(I/O), 3(REG over MEM), 4(CFG) + * + * Return + * 0 Found function + * others No such function defined by host driver or BSP + \*/ + int pci_access_func(int wr, int size, void \**func, int endian, int type); + +PCI device drivers may be written to support run-time detection of endianess, +this is mosly for debugging or for development systems. When the product is +finally deployed macros switch to using the inline functions instead which +have been configured for the correct endianness. + +PCI address translation +~~~~~~~~~~~~~~~~~~~~~~~ + +When PCI addresses, both I/O and memory space, is not mapped 1:1 address +translation before access is needed. If drivers read the PCI resources directly +using configuration space routines or in the device tree, the addresses given +are PCI addresses. The below functions can be used to translate PCI addresses +into CPU accessible addresses or vice versa, translation may be different for +different PCI spaces/regions. +.. code:: c + + /* Translate PCI address into CPU accessible address \*/ + static inline int pci_pci2cpu(uint32_t \*address, int type); + /* Translate CPU accessible address into PCI address (for DMA) \*/ + static inline int pci_cpu2pci(uint32_t \*address, int type); + +PCI Interrupt +------------- + +The PCI specification defines four different interrupt lines INTA#..INTD#, +the interrupts are low level sensitive which make it possible to support +multiple interrupt sources on the same interrupt line. Since the lines are +level sensitive the interrupt sources must be acknowledged before clearing the +interrupt contoller, or the interrupt controller must be masked. The BSP must +provide a routine for clearing/acknowledging the interrupt controller, it is +up to the interrupt service routine to acknowledge the interrupt source. + +The PCI Library relies on the BSP for implementing shared interrupt handling +through the BSP_PCI_shared_interrupt_* functions/macros, they must be defined +when including bsp.h. + +PCI device drivers may use the pci_interrupt_* routines in order to call the +BSP specific functions in a platform independent way. The PCI interrupt +interface has been made similar to the RTEMS IRQ extension so that a BSP can +use the standard RTEMS interrupt functions directly. + +PCI Shell command +----------------- + +The RTEMS shell has a PCI command ’pci’ which makes it possible to read/write +configuration space, print the current PCI configuration and print out a +configuration C-file for the static or peripheral library. + +.. COMMENT: COPYRIGHT (c) 1988-2007. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Stack Bounds Checker +#################### + +Introduction +============ + +The stack bounds checker is an RTEMS support component that determines +if a task has overrun its run-time stack. The routines provided +by the stack bounds checker manager are: + +- ``rtems_stack_checker_is_blown`` - Has the Current Task Blown its Stack + +- ``rtems_stack_checker_report_usage`` - Report Task Stack Usage + +Background +========== + +Task Stack +---------- + +Each task in a system has a fixed size stack associated with it. This +stack is allocated when the task is created. As the task executes, the +stack is used to contain parameters, return addresses, saved registers, +and local variables. The amount of stack space required by a task +is dependent on the exact set of routines used. The peak stack usage +reflects the worst case of subroutine pushing information on the stack. +For example, if a subroutine allocates a local buffer of 1024 bytes, then +this data must be accounted for in the stack of every task that invokes that +routine. + +Recursive routines make calculating peak stack usage difficult, if not +impossible. Each call to the recursive routine consumes *n* bytes +of stack space. If the routine recursives 1000 times, then ``1000 * *n*`` bytes of stack space are required. + +Execution +--------- + +The stack bounds checker operates as a set of task extensions. At +task creation time, the task’s stack is filled with a pattern to +indicate the stack is unused. As the task executes, it will overwrite +this pattern in memory. At each task switch, the stack bounds checker’s +task switch extension is executed. This extension checks that: + +- the last ``n`` bytes of the task’s stack have + not been overwritten. If this pattern has been damaged, it + indicates that at some point since this task was context + switch to the CPU, it has used too much stack space. + +- the current stack pointer of the task is not within + the address range allocated for use as the task’s stack. + +If either of these conditions is detected, then a blown stack +error is reported using the ``printk`` routine. + +The number of bytes checked for an overwrite is processor family dependent. +The minimum stack frame per subroutine call varies widely between processor +families. On CISC families like the Motorola MC68xxx and Intel ix86, all +that is needed is a return address. On more complex RISC processors, +the minimum stack frame per subroutine call may include space to save +a significant number of registers. + +Another processor dependent feature that must be taken into account by +the stack bounds checker is the direction that the stack grows. On some +processor families, the stack grows up or to higher addresses as the +task executes. On other families, it grows down to lower addresses. The +stack bounds checker implementation uses the stack description definitions +provided by every RTEMS port to get for this information. + +Operations +========== + +Initializing the Stack Bounds Checker +------------------------------------- + +The stack checker is initialized automatically when its task +create extension runs for the first time. + +The application must include the stack bounds checker extension set +in its set of Initial Extensions. This set of extensions is +defined as ``STACK_CHECKER_EXTENSION``. If using ```` +for Configuration Table generation, then all that is necessary is +to define the macro ``CONFIGURE_STACK_CHECKER_ENABLED`` before including```` as shown below: +.. code:: c + + #define CONFIGURE_STACK_CHECKER_ENABLED + ... + #include + +Checking for Blown Task Stack +----------------------------- + +The application may check whether the stack pointer of currently +executing task is within proper bounds at any time by calling +the ``rtems_stack_checker_is_blown`` method. This +method return ``FALSE`` if the task is operating within its +stack bounds and has not damaged its pattern area. + +Reporting Task Stack Usage +-------------------------- + +The application may dynamically report the stack usage for every task +in the system by calling the``rtems_stack_checker_report_usage`` routine. +This routine prints a table with the peak usage and stack size of +every task in the system. The following is an example of the +report generated: +.. code:: c + + ID NAME LOW HIGH AVAILABLE USED + 0x04010001 IDLE 0x003e8a60 0x003e9667 2952 200 + 0x08010002 TA1 0x003e5750 0x003e7b57 9096 1168 + 0x08010003 TA2 0x003e31c8 0x003e55cf 9096 1168 + 0x08010004 TA3 0x003e0c40 0x003e3047 9096 1104 + 0xffffffff INTR 0x003ecfc0 0x003effbf 12160 128 + +Notice the last time. The task id is 0xffffffff and its name is "INTR". +This is not actually a task, it is the interrupt stack. + +When a Task Overflows the Stack +------------------------------- + +When the stack bounds checker determines that a stack overflow has occurred, +it will attempt to print a message using ``printk`` identifying the +task and then shut the system down. If the stack overflow has caused +corruption, then it is possible that the message cannot be printed. + +The following is an example of the output generated: +.. code:: c + + BLOWN STACK!!! Offending task(0x3eb360): id=0x08010002; name=0x54413120 + stack covers range 0x003e5750 - 0x003e7b57 (9224 bytes) + Damaged pattern begins at 0x003e5758 and is 128 bytes long + +The above includes the task id and a pointer to the task control block as +well as enough information so one can look at the task’s stack and +see what was happening. + +Routines +======== + +This section details the stack bounds checker’s routines. +A subsection is dedicated to each of routines +and describes the calling sequence, related constants, usage, +and status codes. + +.. COMMENT: rtems_stack_checker_is_blown + +STACK_CHECKER_IS_BLOWN - Has Current Task Blown Its Stack +--------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + bool rtems_stack_checker_is_blown( void ); + +**STATUS CODES:** + +``TRUE`` - Stack is operating within its stack limits +``FALSE`` - Current stack pointer is outside allocated area + +**DESCRIPTION:** + +This method is used to determine if the current stack pointer +of the currently executing task is within bounds. + +**NOTES:** + +This method checks the current stack pointer against +the high and low addresses of the stack memory allocated when +the task was created and it looks for damage to the high water +mark pattern for the worst case usage of the task being called. + +STACK_CHECKER_REPORT_USAGE - Report Task Stack Usage +---------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + void rtems_stack_checker_report_usage( void ); + +**STATUS CODES: NONE** + +**DESCRIPTION:** + +This routine prints a table with the peak stack usage and stack space +allocation of every task in the system. + +**NOTES:** + +NONE + +.. COMMENT: COPYRIGHT (c) 1988-2007. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +CPU Usage Statistics +#################### + +Introduction +============ + +The CPU usage statistics manager is an RTEMS support +component that provides a convenient way to manipulate +the CPU usage information associated with each task +The routines provided by the CPU usage statistics manager are: + +- ``rtems_cpu_usage_report`` - Report CPU Usage Statistics + +- ``rtems_cpu_usage_reset`` - Reset CPU Usage Statistics + +Background +========== + +When analyzing and debugging real-time applications, it is important +to be able to know how much CPU time each task in the system consumes. +This support component provides a mechanism to easily obtain this +information with little burden placed on the target. + +The raw data is gathered as part of performing a context switch. RTEMS +keeps track of how many clock ticks have occurred which the task being +switched out has been executing. If the task has been running less than +1 clock tick, then for the purposes of the statistics, it is assumed to +have executed 1 clock tick. This results in some inaccuracy but the +alternative is for the task to have appeared to execute 0 clock ticks. + +RTEMS versions newer than the 4.7 release series, support the ability +to obtain timestamps with nanosecond granularity if the BSP provides +support. It is a desirable enhancement to change the way the usage +data is gathered to take advantage of this recently added capability. +Please consider sponsoring the core RTEMS development team to add +this capability. + +Operations +========== + +Report CPU Usage Statistics +--------------------------- + +The application may dynamically report the CPU usage for every +task in the system by calling the``rtems_cpu_usage_report`` routine. +This routine prints a table with the following information per task: + +- task id + +- task name + +- number of clock ticks executed + +- percentage of time consumed by this task + +The following is an example of the report generated: + + ++------------------------------------------------------------------------------+ +|CPU USAGE BY THREAD | ++-----------+----------------------------------------+-------------------------+ +|ID | NAME | SECONDS | PERCENT | ++-----------+----------------------------------------+---------------+---------+ +|0x04010001 | IDLE | 0 | 0.000 | ++-----------+----------------------------------------+---------------+---------+ +|0x08010002 | TA1 | 1203 | 0.748 | ++-----------+----------------------------------------+---------------+---------+ +|0x08010003 | TA2 | 203 | 0.126 | ++-----------+----------------------------------------+---------------+---------+ +|0x08010004 | TA3 | 202 | 0.126 | ++-----------+----------------------------------------+---------------+---------+ +|TICKS SINCE LAST SYSTEM RESET: 1600 | +|TOTAL UNITS: 1608 | ++------------------------------------------------------------------------------+ + +Notice that the "TOTAL UNITS" is greater than the ticks per reset. +This is an artifact of the way in which RTEMS keeps track of CPU +usage. When a task is context switched into the CPU, the number +of clock ticks it has executed is incremented. While the task +is executing, this number is incremented on each clock tick. +Otherwise, if a task begins and completes execution between +successive clock ticks, there would be no way to tell that it +executed at all. + +Another thing to keep in mind when looking at idle time, is that +many systems – especially during debug – have a task providing +some type of debug interface. It is usually fine to think of the +total idle time as being the sum of the IDLE task and a debug +task that will not be included in a production build of an application. + +Reset CPU Usage Statistics +-------------------------- + +Invoking the ``rtems_cpu_usage_reset`` routine resets +the CPU usage statistics for all tasks in the system. + +Directives +========== + +This section details the CPU usage statistics manager’s directives. +A subsection is dedicated to each of this manager’s directives +and describes the calling sequence, related constants, usage, +and status codes. + +cpu_usage_report - Report CPU Usage Statistics +---------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + void rtems_cpu_usage_report( void ); + +**STATUS CODES: NONE** + +**DESCRIPTION:** + +This routine prints out a table detailing the CPU usage statistics for +all tasks in the system. + +**NOTES:** + +The table is printed using the ``printk`` routine. + +cpu_usage_reset - Reset CPU Usage Statistics +-------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + void rtems_cpu_usage_reset( void ); + +**STATUS CODES: NONE** + +**DESCRIPTION:** + +This routine re-initializes the CPU usage statistics for all tasks +in the system to their initial state. The initial state is that +a task has not executed and thus has consumed no CPU time. +default state which is when zero period executions have occurred. + +**NOTES:** + +NONE + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Object Services +############### + +.. index:: object manipulation + +Introduction +============ + +RTEMS provides a collection of services to assist in the +management and usage of the objects created and utilized +via other managers. These services assist in the +manipulation of RTEMS objects independent of the API used +to create them. The object related services provided by +RTEMS are: + +- build_id + +- ``rtems_build_name`` - build object name from characters + +- ``rtems_object_get_classic_name`` - lookup name from Id + +- ``rtems_object_get_name`` - obtain object name as string + +- ``rtems_object_set_name`` - set object name + +- ``rtems_object_id_get_api`` - obtain API from Id + +- ``rtems_object_id_get_class`` - obtain class from Id + +- ``rtems_object_id_get_node`` - obtain node from Id + +- ``rtems_object_id_get_index`` - obtain index from Id + +- ``rtems_build_id`` - build object id from components + +- ``rtems_object_id_api_minimum`` - obtain minimum API value + +- ``rtems_object_id_api_maximum`` - obtain maximum API value + +- ``rtems_object_id_api_minimum_class`` - obtain minimum class value + +- ``rtems_object_id_api_maximum_class`` - obtain maximum class value + +- ``rtems_object_get_api_name`` - obtain API name + +- ``rtems_object_get_api_class_name`` - obtain class name + +- ``rtems_object_get_class_information`` - obtain class information + +Background +========== + +APIs +---- + +RTEMS implements multiple APIs including an Internal API, +the Classic API, and the POSIX API. These +APIs share the common foundation of SuperCore objects and +thus share object management code. This includes a common +scheme for object Ids and for managing object names whether +those names be in the thirty-two bit form used by the Classic +API or C strings. + +The object Id contains a field indicating the API that +an object instance is associated with. This field +holds a numerically small non-zero integer. + +Object Classes +-------------- + +Each API consists of a collection of managers. Each manager +is responsible for instances of a particular object class. +Classic API Tasks and POSIX Mutexes example classes. + +The object Id contains a field indicating the class that +an object instance is associated with. This field +holds a numerically small non-zero integer. In all APIs, +a class value of one is reserved for tasks or threads. + +Object Names +------------ + +Every RTEMS object which has an Id may also have a +name associated with it. Depending on the API, names +may be either thirty-two bit integers as in the Classic +API or strings as in the POSIX API. + +Some objects have Ids but do not have a defined way to associate +a name with them. For example, POSIX threads have +Ids but per POSIX do not have names. In RTEMS, objects +not defined to have thirty-two bit names may have string +names assigned to them via the ``rtems_object_set_name`` +service. The original impetus in providing this service +was so the normally anonymous POSIX threads could have +a user defined name in CPU Usage Reports. + +Operations +========== + +Decomposing and Recomposing an Object Id +---------------------------------------- + +Services are provided to decompose an object Id into its +subordinate components. The following services are used +to do this: + +- ``rtems_object_id_get_api`` + +- ``rtems_object_id_get_class`` + +- ``rtems_object_id_get_node`` + +- ``rtems_object_id_get_index`` + +The following C language example illustrates the +decomposition of an Id and printing the values. +.. code:: c + + void printObjectId(rtems_id id) + { + printf( + "API=%d Class=%d Node=%d Index=%d\\n", + rtems_object_id_get_api(id), + rtems_object_id_get_class(id), + rtems_object_id_get_node(id), + rtems_object_id_get_index(id) + ); + } + +This prints the components of the Ids as integers. + +It is also possible to construct an arbitrary Id using +the ``rtems_build_id`` service. The following +C language example illustrates how to construct the +"next Id." +.. code:: c + + rtems_id nextObjectId(rtems_id id) + { + return rtems_build_id( + rtems_object_id_get_api(id), + rtems_object_id_get_class(id), + rtems_object_id_get_node(id), + rtems_object_id_get_index(id) + 1 + ); + } + +Note that this Id may not be valid in this +system or associated with an allocated object. + +Printing an Object Id +--------------------- + +RTEMS also provides services to associate the API and Class +portions of an Object Id with strings. This allows the +application developer to provide more information about +an object in diagnostic messages. + +In the following C language example, an Id is decomposed into +its constituent parts and "pretty-printed." +.. code:: c + + void prettyPrintObjectId(rtems_id id) + { + int tmpAPI, tmpClass; + tmpAPI = rtems_object_id_get_api(id), + tmpClass = rtems_object_id_get_class(id), + printf( + "API=%s Class=%s Node=%d Index=%d\\n", + rtems_object_get_api_name(tmpAPI), + rtems_object_get_api_class_name(tmpAPI, tmpClass), + rtems_object_id_get_node(id), + rtems_object_id_get_index(id) + ); + } + +Directives +========== + +BUILD_NAME - Build object name from characters +---------------------------------------------- +.. index:: build object name + +**CALLING SEQUENCE:** + +.. index:: rtems_build_name + +.. code:: c + + rtems_name rtems_build_name( + uint8_t c1, + uint8_t c2, + uint8_t c3, + uint8_t c4 + ); + +**DIRECTIVE STATUS CODES** + +Returns a name constructed from the four characters. + +**DESCRIPTION:** + +This service takes the four characters provided as arguments +and constructs a thirty-two bit object name with ``c1`` +in the most significant byte and ``c4`` in the least +significant byte. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +OBJECT_GET_CLASSIC_NAME - Lookup name from id +--------------------------------------------- +.. index:: get name from id +.. index:: obtain name from id + +**CALLING SEQUENCE:** + +.. index:: rtems_build_name + +.. code:: c + + rtems_status_code rtems_object_get_classic_name( + rtems_id id, + rtems_name \*name + ); + +**DIRECTIVE STATUS CODES** + +``RTEMS_SUCCESSFUL`` - name looked up successfully +``RTEMS_INVALID_ADDRESS`` - invalid name pointer +``RTEMS_INVALID_ID`` - invalid object id + +**DESCRIPTION:** + +This service looks up the name for the object ``id`` specified +and, if found, places the result in ``*name``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +OBJECT_GET_NAME - Obtain object name as string +---------------------------------------------- +.. index:: get object name as string +.. index:: obtain object name as string + +**CALLING SEQUENCE:** + +.. index:: rtems_object_get_name + +.. code:: c + + char \*rtems_object_get_name( + rtems_id id, + size_t length, + char \*name + ); + +**DIRECTIVE STATUS CODES** + +Returns a pointer to the name if successful or ``NULL`` +otherwise. + +**DESCRIPTION:** + +This service looks up the name of the object specified by``id`` and places it in the memory pointed to by ``name``. +Every attempt is made to return name as a printable string even +if the object has the Classic API thirty-two bit style name. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +OBJECT_SET_NAME - Set object name +--------------------------------- +.. index:: set object name + +**CALLING SEQUENCE:** + +.. index:: rtems_object_set_name + +.. code:: c + + rtems_status_code rtems_object_set_name( + rtems_id id, + const char \*name + ); + +**DIRECTIVE STATUS CODES** + +``RTEMS_SUCCESSFUL`` - name looked up successfully +``RTEMS_INVALID_ADDRESS`` - invalid name pointer +``RTEMS_INVALID_ID`` - invalid object id + +**DESCRIPTION:** + +This service sets the name of ``id`` to that specified +by the string located at ``name``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +If the object specified by ``id`` is of a class that +has a string name, this method will free the existing +name to the RTEMS Workspace and allocate enough memory +from the RTEMS Workspace to make a copy of the string +located at ``name``. + +If the object specified by ``id`` is of a class that +has a thirty-two bit integer style name, then the first +four characters in ``*name`` will be used to construct +the name. +name to the RTEMS Workspace and allocate enough memory +from the RTEMS Workspace to make a copy of the string + +OBJECT_ID_GET_API - Obtain API from Id +-------------------------------------- +.. index:: obtain API from id + +**CALLING SEQUENCE:** + +.. index:: rtems_object_id_get_api + +.. code:: c + + int rtems_object_id_get_api( + rtems_id id + ); + +**DIRECTIVE STATUS CODES** + +Returns the API portion of the object Id. + +**DESCRIPTION:** + +This directive returns the API portion of the provided object ``id``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +This directive does NOT validate the ``id`` provided. + +OBJECT_ID_GET_CLASS - Obtain Class from Id +------------------------------------------ +.. index:: obtain class from object id + +**CALLING SEQUENCE:** + +.. index:: rtems_object_id_get_class + +.. code:: c + + int rtems_object_id_get_class( + rtems_id id + ); + +**DIRECTIVE STATUS CODES** + +Returns the class portion of the object Id. + +**DESCRIPTION:** + +This directive returns the class portion of the provided object ``id``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +This directive does NOT validate the ``id`` provided. + +OBJECT_ID_GET_NODE - Obtain Node from Id +---------------------------------------- +.. index:: obtain node from object id + +**CALLING SEQUENCE:** + +.. index:: rtems_object_id_get_node + +.. code:: c + + int rtems_object_id_get_node( + rtems_id id + ); + +**DIRECTIVE STATUS CODES** + +Returns the node portion of the object Id. + +**DESCRIPTION:** + +This directive returns the node portion of the provided object ``id``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +This directive does NOT validate the ``id`` provided. + +OBJECT_ID_GET_INDEX - Obtain Index from Id +------------------------------------------ +.. index:: obtain index from object id + +**CALLING SEQUENCE:** + +.. index:: rtems_object_id_get_index + +.. code:: c + + int rtems_object_id_get_index( + rtems_id id + ); + +**DIRECTIVE STATUS CODES** + +Returns the index portion of the object Id. + +**DESCRIPTION:** + +This directive returns the index portion of the provided object ``id``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +This directive does NOT validate the ``id`` provided. + +BUILD_ID - Build Object Id From Components +------------------------------------------ +.. index:: build object id from components + +**CALLING SEQUENCE:** + +.. index:: rtems_build_id + +.. code:: c + + rtems_id rtems_build_id( + int the_api, + int the_class, + int the_node, + int the_index + ); + +**DIRECTIVE STATUS CODES** + +Returns an object Id constructed from the provided arguments. + +**DESCRIPTION:** + +This service constructs an object Id from the provided``the_api``, ``the_class``, ``the_node``, and ``the_index``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +This directive does NOT validate the arguments provided +or the Object id returned. + +OBJECT_ID_API_MINIMUM - Obtain Minimum API Value +------------------------------------------------ +.. index:: obtain minimum API value + +**CALLING SEQUENCE:** + +.. index:: rtems_object_id_api_minimum + +.. code:: c + + int rtems_object_id_api_minimum(void); + +**DIRECTIVE STATUS CODES** + +Returns the minimum valid for the API portion of an object Id. + +**DESCRIPTION:** + +This service returns the minimum valid for the API portion of +an object Id. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +OBJECT_ID_API_MAXIMUM - Obtain Maximum API Value +------------------------------------------------ +.. index:: obtain maximum API value + +**CALLING SEQUENCE:** + +.. index:: rtems_object_id_api_maximum + +.. code:: c + + int rtems_object_id_api_maximum(void); + +**DIRECTIVE STATUS CODES** + +Returns the maximum valid for the API portion of an object Id. + +**DESCRIPTION:** + +This service returns the maximum valid for the API portion of +an object Id. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +OBJECT_API_MINIMUM_CLASS - Obtain Minimum Class Value +----------------------------------------------------- +.. index:: obtain minimum class value + +**CALLING SEQUENCE:** + +.. index:: rtems_object_api_minimum_class + +.. code:: c + + int rtems_object_api_minimum_class( + int api + ); + +**DIRECTIVE STATUS CODES** + +If ``api`` is not valid, -1 is returned. + +If successful, this service returns the minimum valid for the class +portion of an object Id for the specified ``api``. + +**DESCRIPTION:** + +This service returns the minimum valid for the class portion of +an object Id for the specified ``api``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +OBJECT_API_MAXIMUM_CLASS - Obtain Maximum Class Value +----------------------------------------------------- +.. index:: obtain maximum class value + +**CALLING SEQUENCE:** + +.. index:: rtems_object_api_maximum_class + +.. code:: c + + int rtems_object_api_maximum_class( + int api + ); + +**DIRECTIVE STATUS CODES** + +If ``api`` is not valid, -1 is returned. + +If successful, this service returns the maximum valid for the class +portion of an object Id for the specified ``api``. + +**DESCRIPTION:** + +This service returns the maximum valid for the class portion of +an object Id for the specified ``api``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +OBJECT_GET_API_NAME - Obtain API Name +------------------------------------- +.. index:: obtain API name + +**CALLING SEQUENCE:** + +.. index:: rtems_object_get_api_name + +.. code:: c + + const char \*rtems_object_get_api_name( + int api + ); + +**DIRECTIVE STATUS CODES** + +If ``api`` is not valid, the string ``"BAD API"`` is returned. + +If successful, this service returns a pointer to a string +containing the name of the specified ``api``. + +**DESCRIPTION:** + +This service returns the name of the specified ``api``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +The string returned is from constant space. Do not modify +or free it. + +OBJECT_GET_API_CLASS_NAME - Obtain Class Name +--------------------------------------------- +.. index:: obtain class name + +**CALLING SEQUENCE:** + +.. index:: rtems_object_get_api_class_name + +.. code:: c + + const char \*rtems_object_get_api_class_name( + int the_api, + int the_class + ); + +**DIRECTIVE STATUS CODES** + +If ``the_api`` is not valid, the string ``"BAD API"`` is returned. + +If ``the_class`` is not valid, the string ``"BAD CLASS"`` is returned. + +If successful, this service returns a pointer to a string +containing the name of the specified ``the_api``/``the_class`` pair. + +**DESCRIPTION:** + +This service returns the name of the object class indicated by the +specified ``the_api`` and ``the_class``. + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +The string returned is from constant space. Do not modify +or free it. + +OBJECT_GET_CLASS_INFORMATION - Obtain Class Information +------------------------------------------------------- +.. index:: obtain class information + +**CALLING SEQUENCE:** + +.. index:: rtems_object_get_class_information + +.. code:: c + + rtems_status_code rtems_object_get_class_information( + int the_api, + int the_class, + rtems_object_api_class_information \*info + ); + +**DIRECTIVE STATUS CODES** + +``RTEMS_SUCCESSFUL`` - information obtained successfully +``RTEMS_INVALID_ADDRESS`` - ``info`` is NULL +``RTEMS_INVALID_NUMBER`` - invalid ``api`` or ``the_class`` + +If successful, the structure located at ``info`` will be filled +in with information about the specified ``api``/``the_class`` pairing. + +**DESCRIPTION:** + +This service returns information about the object class indicated by the +specified ``api`` and ``the_class``. This structure is defined as +follows: +.. code:: c + + typedef struct { + rtems_id minimum_id; + rtems_id maximum_id; + int maximum; + bool auto_extend; + int unallocated; + } rtems_object_api_class_information; + +**NOTES:** + +This directive is strictly local and does not impact task scheduling. + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Chains +###### + +.. index:: chains + +Introduction +============ + +The Chains API is an interface to the Super Core (score) chain +implementation. The Super Core uses chains for all list type +functions. This includes wait queues and task queues. The Chains API +provided by RTEMS is: + +- build_id + +- ``rtems_chain_node`` - Chain node used in user objects + +- ``rtems_chain_control`` - Chain control node + +- ``rtems_chain_initialize`` - initialize the chain with nodes + +- ``rtems_chain_initialize_empty`` - initialize the chain as empty + +- ``rtems_chain_is_null_node`` - Is the node NULL ? + +- ``rtems_chain_head`` - Return the chain’s head + +- ``rtems_chain_tail`` - Return the chain’s tail + +- ``rtems_chain_are_nodes_equal`` - Are the node’s equal ? + +- ``rtems_chain_is_empty`` - Is the chain empty ? + +- ``rtems_chain_is_first`` - Is the Node the first in the chain ? + +- ``rtems_chain_is_last`` - Is the Node the last in the chain ? + +- ``rtems_chain_has_only_one_node`` - Does the node have one node ? + +- ``rtems_chain_node_count_unprotected`` - Returns the node count of the chain (unprotected) + +- ``rtems_chain_is_head`` - Is the node the head ? + +- ``rtems_chain_is_tail`` - Is the node the tail ? + +- ``rtems_chain_extract`` - Extract the node from the chain + +- ``rtems_chain_extract_unprotected`` - Extract the node from the chain (unprotected) + +- ``rtems_chain_get`` - Return the first node on the chain + +- ``rtems_chain_get_unprotected`` - Return the first node on the chain (unprotected) + +- ``rtems_chain_get_first_unprotected`` - Get the first node on the chain (unprotected) + +- ``rtems_chain_insert`` - Insert the node into the chain + +- ``rtems_chain_insert_unprotected`` - Insert the node into the chain (unprotected) + +- ``rtems_chain_append`` - Append the node to chain + +- ``rtems_chain_append_unprotected`` - Append the node to chain (unprotected) + +- ``rtems_chain_prepend`` - Prepend the node to the end of the chain + +- ``rtems_chain_prepend_unprotected`` - Prepend the node to chain (unprotected) + +Background +========== + +The Chains API maps to the Super Core Chains API. Chains are +implemented as a double linked list of nodes anchored to a control +node. The list starts at the control node and is terminated at the +control node. A node has previous and next pointers. Being a double +linked list nodes can be inserted and removed without the need to +travse the chain. + +Chains have a small memory footprint and can be used in interrupt +service routines and are thread safe in a multi-threaded +environment. The directives list which operations disable interrupts. + +Chains are very useful in Board Support packages and applications. + +Nodes +----- + +A chain is made up from nodes that orginate from a chain control +object. A node is of type ``rtems_chain_node``. The node +is designed to be part of a user data structure and a cast is used to +move from the node address to the user data structure address. For +example: +.. code:: c + + typedef struct foo + { + rtems_chain_node node; + int bar; + } foo; + +creates a type ``foo`` that can be placed on a chain. To get the +foo structure from the list you perform the following: +.. code:: c + + foo* get_foo(rtems_chain_control* control) + { + return (foo*) rtems_chain_get(control); + } + +The node is placed at the start of the user’s structure to allow the +node address on the chain to be easly cast to the user’s structure +address. + +Controls +-------- + +A chain is anchored with a control object. Chain control provide the +user with access to the nodes on the chain. The control is head of the +node. + +.. code:: c + + Control + first ------------------------> + permanent_null <--------------- NODE + last -------------------------> + +The implementation does not require special checks for manipulating +the first and last nodes on the chain. To accomplish this the``rtems_chain_control`` structure is treated as two +overlapping ``rtems_chain_node`` structures. The +permanent head of the chain overlays a node structure on the first and``permanent_null`` fields. The ``permanent_tail`` of the chain +overlays a node structure on the ``permanent_null`` and ``last`` +elements of the structure. + +Operations +========== + +Multi-threading +--------------- + +Chains are designed to be used in a multi-threading environment. The +directives list which operations mask interrupts. Chains supports +tasks and interrupt service routines appending and extracting nodes +with out the need for extra locks. Chains how-ever cannot insure the +integrity of a chain for all operations. This is the responsibility of +the user. For example an interrupt service routine extracting nodes +while a task is iterating over the chain can have unpredictable +results. + +Creating a Chain +---------------- + +To create a chain you need to declare a chain control then add nodes +to the control. Consider a user structure and chain control: +.. code:: c + + typedef struct foo + { + rtems_chain_node node; + uint8_t char* data; + } foo; + rtems_chain_control chain; + +Add nodes with the following code: +.. code:: c + + rtems_chain_initialize_empty (&chain); + for (i = 0; i < count; i++) + { + foo* bar = malloc (sizeof (foo)); + if (!bar) + return -1; + bar->data = malloc (size); + rtems_chain_append (&chain, &bar->node); + } + +The chain is initialized and the nodes allocated and appended to the +chain. This is an example of a pool of buffers. + +Iterating a Chain +----------------- +.. index:: chain iterate + +Iterating a chain is a common function. The example shows how to +iterate the buffer pool chain created in the last section to find +buffers starting with a specific string. If the buffer is located it is +extracted from the chain and placed on another chain: +.. code:: c + + void foobar (const char* match, + rtems_chain_control* chain, + rtems_chain_control* out) + { + rtems_chain_node* node; + foo* bar; + rtems_chain_initialize_empty (out); + node = chain->first; + while (!rtems_chain_is_tail (chain, node)) + { + bar = (foo*) node; + rtems_chain_node* next_node = node->next; + if (strcmp (match, bar->data) == 0) + { + rtems_chain_extract (node); + rtems_chain_append (out, node); + } + node = next_node; + } + } + +Directives +========== + +The section details the Chains directives. + +.. COMMENT: Initialize this Chain With Nodes + +Initialize Chain With Nodes +--------------------------- +.. index:: chain initialize + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_initialize + +.. code:: c + + void rtems_chain_initialize( + rtems_chain_control \*the_chain, + void \*starting_address, + size_t number_nodes, + size_t node_size + ) + +**RETURNS** + +Returns nothing. + +**DESCRIPTION:** + +This function take in a pointer to a chain control and initializes it +to contain a set of chain nodes. The chain will contain ``number_nodes`` +chain nodes from the memory pointed to by ``start_address``. Each node +is assumed to be ``node_size`` bytes. + +**NOTES:** + +This call will discard any nodes on the chain. + +This call does NOT inititialize any user data on each node. + +.. COMMENT: Initialize this Chain as Empty + +Initialize Empty +---------------- +.. index:: chain initialize empty + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_initialize_empty + +.. code:: c + + void rtems_chain_initialize_empty( + rtems_chain_control \*the_chain + ); + +**RETURNS** + +Returns nothing. + +**DESCRIPTION:** + +This function take in a pointer to a chain control and initializes it +to empty. + +**NOTES:** + +This call will discard any nodes on the chain. + +Is Null Node ? +-------------- +.. index:: chain is node null + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_is_null_node + +.. code:: c + + bool rtems_chain_is_null_node( + const rtems_chain_node \*the_node + ); + +**RETURNS** + +Returns ``true`` is the node point is NULL and ``false`` if the node is not +NULL. + +**DESCRIPTION:** + +Tests the node to see if it is a NULL returning ``true`` if a null. + +Head +---- +.. index:: chain get head + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_head + +.. code:: c + + rtems_chain_node \*rtems_chain_head( + rtems_chain_control \*the_chain + ) + +**RETURNS** + +Returns the permanent head node of the chain. + +**DESCRIPTION:** + +This function returns a pointer to the first node on the chain. + +Tail +---- +.. index:: chain get tail + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_tail + +.. code:: c + + rtems_chain_node \*rtems_chain_tail( + rtems_chain_control \*the_chain + ); + +**RETURNS** + +Returns the permanent tail node of the chain. + +**DESCRIPTION:** + +This function returns a pointer to the last node on the chain. + +Are Two Nodes Equal ? +--------------------- +.. index:: chare are nodes equal + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_are_nodes_equal + +.. code:: c + + bool rtems_chain_are_nodes_equal( + const rtems_chain_node \*left, + const rtems_chain_node \*right + ); + +**RETURNS** + +This function returns ``true`` if the left node and the right node are +equal, and ``false`` otherwise. + +**DESCRIPTION:** + +This function returns ``true`` if the left node and the right node are +equal, and ``false`` otherwise. + +Is the Chain Empty +------------------ +.. index:: chain is chain empty + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_is_empty + +.. code:: c + + bool rtems_chain_is_empty( + rtems_chain_control \*the_chain + ); + +**RETURNS** + +This function returns ``true`` if there a no nodes on the chain and ``false`` +otherwise. + +**DESCRIPTION:** + +This function returns ``true`` if there a no nodes on the chain and ``false`` +otherwise. + +Is this the First Node on the Chain ? +------------------------------------- +.. index:: chain is node the first + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_is_first + +.. code:: c + + bool rtems_chain_is_first( + const rtems_chain_node \*the_node + ); + +**RETURNS** + +This function returns ``true`` if the node is the first node on a chain +and ``false`` otherwise. + +**DESCRIPTION:** + +This function returns ``true`` if the node is the first node on a chain +and ``false`` otherwise. + +Is this the Last Node on the Chain ? +------------------------------------ +.. index:: chain is node the last + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_is_last + +.. code:: c + + bool rtems_chain_is_last( + const rtems_chain_node \*the_node + ); + +**RETURNS** + +This function returns ``true`` if the node is the last node on a chain and``false`` otherwise. + +**DESCRIPTION:** + +This function returns ``true`` if the node is the last node on a chain and``false`` otherwise. + +Does this Chain have only One Node ? +------------------------------------ +.. index:: chain only one node + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_has_only_one_node + +.. code:: c + + bool rtems_chain_has_only_one_node( + const rtems_chain_control \*the_chain + ); + +**RETURNS** + +This function returns ``true`` if there is only one node on the chain and``false`` otherwise. + +**DESCRIPTION:** + +This function returns ``true`` if there is only one node on the chain and``false`` otherwise. + +Returns the node count of the chain (unprotected) +------------------------------------------------- +.. index:: chain only one node + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_node_count_unprotected + +.. code:: c + + size_t rtems_chain_node_count_unprotected( + const rtems_chain_control \*the_chain + ); + +**RETURNS** + +This function returns the node count of the chain. + +**DESCRIPTION:** + +This function returns the node count of the chain. + +Is this Node the Chain Head ? +----------------------------- +.. index:: chain is node the head + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_is_head + +.. code:: c + + bool rtems_chain_is_head( + rtems_chain_control \*the_chain, + rtems_const chain_node \*the_node + ); + +**RETURNS** + +This function returns ``true`` if the node is the head of the chain and``false`` otherwise. + +**DESCRIPTION:** + +This function returns ``true`` if the node is the head of the chain and``false`` otherwise. + +Is this Node the Chain Tail ? +----------------------------- +.. index:: chain is node the tail + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_is_tail + +.. code:: c + + bool rtems_chain_is_tail( + rtems_chain_control \*the_chain, + const rtems_chain_node \*the_node + ) + +**RETURNS** + +This function returns ``true`` if the node is the tail of the chain and``false`` otherwise. + +**DESCRIPTION:** + +This function returns ``true`` if the node is the tail of the chain and``false`` otherwise. + +Extract a Node +-------------- +.. index:: chain extract a node + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_extract + +.. code:: c + + void rtems_chain_extract( + rtems_chain_node \*the_node + ); + +**RETURNS** + +Returns nothing. + +**DESCRIPTION:** + +This routine extracts the node from the chain on which it resides. + +**NOTES:** + +Interrupts are disabled while extracting the node to ensure the +atomicity of the operation. + +Use ``rtems_chain_extract_unprotected()`` to avoid disabling of +interrupts. + +Get the First Node +------------------ +.. index:: chain get first node + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_get + +.. code:: c + + rtems_chain_node \*rtems_chain_get( + rtems_chain_control \*the_chain + ); + +**RETURNS** + +Returns a pointer a node. If a node was removed, then a pointer to +that node is returned. If the chain was empty, then NULL is +returned. + +**DESCRIPTION:** + +This function removes the first node from the chain and returns a +pointer to that node. If the chain is empty, then NULL is returned. + +**NOTES:** + +Interrupts are disabled while obtaining the node to ensure the +atomicity of the operation. + +Use ``rtems_chain_get_unprotected()`` to avoid disabling of +interrupts. + +Get the First Node (unprotected) +-------------------------------- +.. index:: chain get first node + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_get_first_unprotected + +.. code:: c + + rtems_chain_node \*rtems_chain_get_first_unprotected( + rtems_chain_control \*the_chain + ); + +**RETURNS:** + +A pointer to the former first node is returned. + +**DESCRIPTION:** + +Removes the first node from the chain and returns a pointer to it. In case the +chain was empty, then the results are unpredictable. + +**NOTES:** + +The function does nothing to ensure the atomicity of the operation. + +Insert a Node +------------- +.. index:: chain insert a node + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_insert + +.. code:: c + + void rtems_chain_insert( + rtems_chain_node \*after_node, + rtems_chain_node \*the_node + ); + +**RETURNS** + +Returns nothing. + +**DESCRIPTION:** + +This routine inserts a node on a chain immediately following the +specified node. + +**NOTES:** + +Interrupts are disabled during the insert to ensure the atomicity of +the operation. + +Use ``rtems_chain_insert_unprotected()`` to avoid disabling of +interrupts. + +Append a Node +------------- +.. index:: chain append a node + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_append + +.. code:: c + + void rtems_chain_append( + rtems_chain_control \*the_chain, + rtems_chain_node \*the_node + ); + +**RETURNS** + +Returns nothing. + +**DESCRIPTION:** + +This routine appends a node to the end of a chain. + +**NOTES:** + +Interrupts are disabled during the append to ensure the atomicity of +the operation. + +Use ``rtems_chain_append_unprotected()`` to avoid disabling of +interrupts. + +Prepend a Node +-------------- +.. index:: prepend node + +**CALLING SEQUENCE:** + +.. index:: rtems_chain_prepend + +.. code:: c + + void rtems_chain_prepend( + rtems_chain_control \*the_chain, + rtems_chain_node \*the_node + ); + +**RETURNS** + +Returns nothing. + +**DESCRIPTION:** + +This routine prepends a node to the front of the chain. + +**NOTES:** + +Interrupts are disabled during the prepend to ensure the atomicity of +the operation. + +Use ``rtems_chain_prepend_unprotected()`` to avoid disabling of +interrupts. + +.. COMMENT: Copyright 2014 Gedare Bloom. + +.. COMMENT: All rights reserved. + +Red-Black Trees +############### + +.. index:: rbtrees + +Introduction +============ + +The Red-Black Tree API is an interface to the SuperCore (score) rbtree +implementation. Within RTEMS, red-black trees are used when a binary search +tree is needed, including dynamic priority thread queues and non-contiguous +heap memory. The Red-Black Tree API provided by RTEMS is: + +- build_id + +- ``rtems_rtems_rbtree_node`` - Red-Black Tree node embedded in another struct + +- ``rtems_rtems_rbtree_control`` - Red-Black Tree control node for an entire tree + +- ``rtems_rtems_rbtree_initialize`` - initialize the red-black tree with nodes + +- ``rtems_rtems_rbtree_initialize_empty`` - initialize the red-black tree as empty + +- ``rtems_rtems_rbtree_set_off_tree`` - Clear a node’s links + +- ``rtems_rtems_rbtree_root`` - Return the red-black tree’s root node + +- ``rtems_rtems_rbtree_min`` - Return the red-black tree’s minimum node + +- ``rtems_rtems_rbtree_max`` - Return the red-black tree’s maximum node + +- ``rtems_rtems_rbtree_left`` - Return a node’s left child node + +- ``rtems_rtems_rbtree_right`` - Return a node’s right child node + +- ``rtems_rtems_rbtree_parent`` - Return a node’s parent node + +- ``rtems_rtems_rbtree_are_nodes_equal`` - Are the node’s equal ? + +- ``rtems_rtems_rbtree_is_empty`` - Is the red-black tree empty ? + +- ``rtems_rtems_rbtree_is_min`` - Is the Node the minimum in the red-black tree ? + +- ``rtems_rtems_rbtree_is_max`` - Is the Node the maximum in the red-black tree ? + +- ``rtems_rtems_rbtree_is_root`` - Is the Node the root of the red-black tree ? + +- ``rtems_rtems_rbtree_find`` - Find the node with a matching key in the red-black tree + +- ``rtems_rtems_rbtree_predecessor`` - Return the in-order predecessor of a node. + +- ``rtems_rtems_rbtree_successor`` - Return the in-order successor of a node. + +- ``rtems_rtems_rbtree_extract`` - Remove the node from the red-black tree + +- ``rtems_rtems_rbtree_get_min`` - Remove the minimum node from the red-black tree + +- ``rtems_rtems_rbtree_get_max`` - Remove the maximum node from the red-black tree + +- ``rtems_rtems_rbtree_peek_min`` - Returns the minimum node from the red-black tree + +- ``rtems_rtems_rbtree_peek_max`` - Returns the maximum node from the red-black tree + +- ``rtems_rtems_rbtree_insert`` - Add the node to the red-black tree + +Background +========== + +The Red-Black Trees API is a thin layer above the SuperCore Red-Black Trees +implementation. A Red-Black Tree is defined by a control node with pointers to +the root, minimum, and maximum nodes in the tree. Each node in the tree +consists of a parent pointer, two children pointers, and a color attribute. A +tree is parameterized as either unique, meaning identical keys are rejected, or +not, in which case duplicate keys are allowed. + +Users must provide a comparison functor that gets passed to functions that need +to compare nodes. In addition, no internal synchronization is offered within +the red-black tree implementation, thus users must ensure at most one thread +accesses a red-black tree instance at a time. + +Nodes +----- + +A red-black tree is made up from nodes that orginate from a red-black tree control +object. A node is of type ``rtems_rtems_rbtree_node``. The node +is designed to be part of a user data structure. To obtain the encapsulating +structure users can use the ``RTEMS_CONTAINER_OF`` macro. +The node can be placed anywhere within the user’s structure and the macro will +calculate the structure’s address from the node’s address. + +Controls +-------- + +A red-black tree is rooted with a control object. Red-Black Tree control +provide the user with access to the nodes on the red-black tree. The +implementation does not require special checks for manipulating the root of the +red-black tree. To accomplish this the``rtems_rtems_rbtree_control`` structure is treated as a``rtems_rtems_rbtree_node`` structure with a ``NULL`` parent +and left child pointing to the root. + +Operations +========== + +Examples for using the red-black trees +can be found in the testsuites/sptests/sprbtree01/init.c file. + +Directives +========== + +Documentation for the Red-Black Tree Directives +----------------------------------------------- +.. index:: rbtree doc + +Source documentation for the Red-Black Tree API can be found in the +generated Doxygen output for cpukit/sapi. + +.. COMMENT: COPYRIGHT (c) 1988-2012. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Timespec Helpers +################ + +Introduction +============ + +The Timespec helpers manager provides directives to assist in manipulating +instances of the POSIX ``struct timespec`` structure. + +The directives provided by the timespec helpers manager are: + +- ``rtems_timespec_set`` - Set timespec’s value + +- ``rtems_timespec_zero`` - Zero timespec’s value + +- ``rtems_timespec_is_valid`` - Check if timespec is valid + +- ``rtems_timespec_add_to`` - Add two timespecs + +- ``rtems_timespec_subtract`` - Subtract two timespecs + +- ``rtems_timespec_divide`` - Divide two timespecs + +- ``rtems_timespec_divide_by_integer`` - Divide timespec by integer + +- ``rtems_timespec_less_than`` - Less than operator + +- ``rtems_timespec_greater_than`` - Greater than operator + +- ``rtems_timespec_equal_to`` - Check if two timespecs are equal + +- ``rtems_timespec_get_seconds`` - Obtain seconds portion of timespec + +- ``rtems_timespec_get_nanoseconds`` - Obtain nanoseconds portion of timespec + +- ``rtems_timespec_to_ticks`` - Convert timespec to number of ticks + +- ``rtems_timespec_from_ticks`` - Convert ticks to timespec + +Background +========== + +Time Storage Conventions +------------------------ + +Time can be stored in many ways. One of them is the ``struct timespec`` +format which is a structure that consists of the fields ``tv_sec`` +to represent seconds and ``tv_nsec`` to represent nanoseconds. The``struct timeval`` structure is simular and consists of seconds (stored +in ``tv_sec``) and microseconds (stored in ``tv_usec``). Either``struct timespec`` or ``struct timeval`` can be used to represent +elapsed time, time of executing some operations, or time of day. + +Operations +========== + +Set and Obtain Timespec Value +----------------------------- + +A user may write a specific time by passing the desired seconds and +nanoseconds values and the destination ``struct timespec`` using the``rtems_timespec_set`` directive. + +The ``rtems_timespec_zero`` directive is used to zero the seconds +and nanoseconds portions of a ``struct timespec`` instance. + +Users may obtain the seconds or nanoseconds portions of a ``struct +timespec`` instance with the ``rtems_timespec_get_seconds`` or``rtems_timespec_get_nanoseconds`` methods, respectively. + +Timespec Math +------------- + +A user can perform multiple operations on ``struct timespec`` +instances. The helpers in this manager assist in adding, subtracting, and +performing divison on ``struct timespec`` instances. + +- Adding two ``struct timespec`` can be done using the``rtems_timespec_add_to`` directive. This directive is used mainly + to calculate total amount of time consumed by multiple operations. + +- The ``rtems_timespec_subtract`` is used to subtract two``struct timespecs`` instances and determine the elapsed time between + those two points in time. + +- The ``rtems_timespec_divide`` is used to use to divide one``struct timespec`` instance by another. This calculates the percentage + with a precision to three decimal points. + +- The ``rtems_timespec_divide_by_integer`` is used to divide a``struct timespec`` instance by an integer. It is commonly used in + benchmark calculations to dividing duration by the number of iterations + performed. + +Comparing struct timespec Instances +----------------------------------- + +A user can compare two ``struct timespec`` instances using the``rtems_timespec_less_than``, ``rtems_timespec_greater_than`` +or ``rtems_timespec_equal_to`` routines. + +Conversions and Validity Check +------------------------------ + +Conversion to and from clock ticks may be performed by using the``rtems_timespec_to_ticks`` and ``rtems_timespec_from_ticks`` +directives. + +User can also check validity of timespec with``rtems_timespec_is_valid`` routine. + +Directives +========== + +This section details the Timespec Helpers manager’s directives. +A subsection is dedicated to each of this manager’s directives +and describes the calling sequence, related constants, usage, +and status codes. + +TIMESPEC_SET - Set struct timespec Instance +------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + void rtems_timespec_set( + struct timespec \*time, + time_t seconds, + uint32_t nanoseconds + ); + +.. index:: rtems_timespec_set + +**STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This directive sets the ``struct timespec`` ``time`` value to the +desired ``seconds`` and ``nanoseconds`` values. + +**NOTES:** + +This method does NOT check if ``nanoseconds`` is less than the +maximum number of nanoseconds in a second. + +TIMESPEC_ZERO - Zero struct timespec Instance +--------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + void rtems_timespec_zero( + struct timespec \*time + ); + +.. index:: rtems_timespec_zero + +**STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This routine sets the contents of the ``struct timespec`` instance``time`` to zero. + +**NOTES:** + +NONE + +TIMESPEC_IS_VALID - Check validity of a struct timespec instance +---------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + bool rtems_timespec_is_valid( + const struct timespec \*time + ); + +.. index:: rtems_timespec_is_valid + +**STATUS CODES:** + +This method returns ``true`` if the instance is valid, and ``false`` +otherwise. + +**DESCRIPTION:** + +This routine check validity of a ``struct timespec`` instance. It +checks if the nanoseconds portion of the ``struct timespec`` instanceis +in allowed range (less than the maximum number of nanoseconds per second). + +**NOTES:** + +TIMESPEC_ADD_TO - Add Two struct timespec Instances +--------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + uint32_t rtems_timespec_add_to( + struct timespec \*time, + const struct timespec \*add + ); + +.. index:: rtems_timespec_add_to + +**STATUS CODES:** + +The method returns the number of seconds ``time`` increased by. + +**DESCRIPTION:** + +This routine adds two ``struct timespec`` instances. The second argument is added to the first. The parameter ``time`` is the base time to which the ``add`` parameter is added. + +**NOTES:** + +NONE + +TIMESPEC_SUBTRACT - Subtract Two struct timespec Instances +---------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + void rtems_timespec_subtract( + const struct timespec \*start, + const struct timespec \*end, + struct timespec \*result + ); + +.. index:: rtems_timespec_subtract + +**STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This routine subtracts ``start`` from ``end`` saves the difference +in ``result``. The primary use of this directive is to calculate +elapsed time. + +**NOTES:** + +It is possible to subtract when ``end`` is less than ``start`` +and it produce negative ``result``. When doing this you should be +careful and remember that only the seconds portion of a ``struct +timespec`` instance is signed, which means that nanoseconds portion is +always increasing. Due to that when your timespec has seconds = -1 and +nanoseconds=500,000,000 it means that result is -0.5 second, NOT the +expected -1.5! + +TIMESPEC_DIVIDE - Divide Two struct timespec Instances +------------------------------------------------------ + +**CALLING SEQUENCE:** + +.. code:: c + + void rtems_timespec_divide( + const struct timespec \*lhs, + const struct timespec \*rhs, + uint32_t \*ival_percentage, + uint32_t \*fval_percentage + ); + +.. index:: rtems_timespec_divide + +**STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This routine divides the ``struct timespec`` instance ``lhs`` by +the ``struct timespec`` instance ``rhs``. The result is returned +in the ``ival_percentage`` and ``fval_percentage``, representing +the integer and fractional results of the division respectively. + +The ``ival_percentage`` is integer value of calculated percentage and ``fval_percentage`` is fractional part of calculated percentage. + +**NOTES:** + +The intended use is calculating percentges to three decimal points. + +When dividing by zero, this routine return both ``ival_percentage`` +and ``fval_percentage`` equal zero. + +The division is performed using exclusively integer operations. + +TIMESPEC_DIVIDE_BY_INTEGER - Divide a struct timespec Instance by an Integer +---------------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + int rtems_timespec_divide_by_integer( + const struct timespec \*time, + uint32_t iterations, + struct timespec \*result + ); + +.. index:: rtems_timespec_divide_by_integer + +**STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This routine divides the ``struct timespec`` instance ``time`` by the integer value ``iterations``. +The result is saved in ``result``. + +**NOTES:** + +The expected use is to assist in benchmark calculations where you +typically divide a duration (``time``) by a number of iterations what +gives average time. + +TIMESPEC_LESS_THAN - Less than operator +--------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + bool rtems_timespec_less_than( + const struct timespec \*lhs, + const struct timespec \*rhs + ); + +.. index:: rtems_timespec_less_than + +**STATUS CODES:** + +This method returns ``struct true`` if ``lhs`` is less than``rhs`` and ``struct false`` otherwise. + +**DESCRIPTION:** + +This method is the less than operator for ``struct timespec`` instances. The first parameter is the left hand side and the second is the right hand side of the comparison. + +**NOTES:** + +NONE + +TIMESPEC_GREATER_THAN - Greater than operator +--------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + bool rtems_timespec_greater_than( + const struct timespec \*_lhs, + const struct timespec \*_rhs + ); + +.. index:: rtems_timespec_greater_than + +**STATUS CODES:** + +This method returns ``struct true`` if ``lhs`` is greater than``rhs`` and ``struct false`` otherwise. + +**DESCRIPTION:** + +This method is greater than operator for ``struct timespec`` instances. + +**NOTES:** + +NONE + +TIMESPEC_EQUAL_TO - Check equality of timespecs +----------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + bool rtems_timespec_equal_to( + const struct timespec \*lhs, + const struct timespec \*rhs + ); + +.. index:: rtems_timespec_equal_to + +**STATUS CODES:** + +This method returns ``struct true`` if ``lhs`` is equal to``rhs`` and ``struct false`` otherwise. + +**DESCRIPTION:** + +This method is equality operator for ``struct timespec`` instances. + +**NOTES:** + +NONE + +TIMESPEC_GET_SECONDS - Get Seconds Portion of struct timespec Instance +---------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + time_t rtems_timespec_get_seconds( + struct timespec \*time + ); + +.. index:: rtems_timespec_get_seconds + +**STATUS CODES:** + +This method returns the seconds portion of the specified ``struct +timespec`` instance. + +**DESCRIPTION:** + +This method returns the seconds portion of the specified ``struct timespec`` instance ``time``. + +**NOTES:** + +NONE + +TIMESPEC_GET_NANOSECONDS - Get Nanoseconds Portion of the struct timespec Instance +---------------------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + uint32_t rtems_timespec_get_nanoseconds( + struct timespec \*_time + ); + +.. index:: rtems_timespec_get_nanoseconds + +**STATUS CODES:** + +This method returns the nanoseconds portion of the specified ``struct +timespec`` instance. + +**DESCRIPTION:** + +This method returns the nanoseconds portion of the specified timespec +which is pointed by ``_time``. + +**NOTES:** + +TIMESPEC_TO_TICKS - Convert struct timespec Instance to Ticks +------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + uint32_t rtems_timespec_to_ticks( + const struct timespec \*time + ); + +.. index:: rtems_timespec_to_ticks + +**STATUS CODES:** + +This directive returns the number of ticks computed. + +**DESCRIPTION:** + +This directive converts the ``time`` timespec to the corresponding number of clock ticks. + +**NOTES:** + +NONE + +TIMESPEC_FROM_TICKS - Convert Ticks to struct timespec Representation +--------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. code:: c + + void rtems_timespec_from_ticks( + uint32_t ticks, + struct timespec \*time + ); + +.. index:: rtems_timespec_from_ticks + +**STATUS CODES:** + +NONE + +**DESCRIPTION:** + +This routine converts the ``ticks`` to the corresponding ``struct timespec`` representation and stores it in ``time``. + +**NOTES:** + +NONE + +.. COMMENT: COPYRIGHT (c) 2011. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Constant Bandwidth Server Scheduler API +####################################### + +.. index:: cbs + +Introduction +============ + +Unlike simple schedulers, the Constant Bandwidth Server (CBS) requires +a special API for tasks to indicate their scheduling parameters. +The directives provided by the CBS API are: + +- ``rtems_cbs_initialize`` - Initialize the CBS library + +- ``rtems_cbs_cleanup`` - Cleanup the CBS library + +- ``rtems_cbs_create_server`` - Create a new bandwidth server + +- ``rtems_cbs_attach_thread`` - Attach a thread to server + +- ``rtems_cbs_detach_thread`` - Detach a thread from server + +- ``rtems_cbs_destroy_server`` - Destroy a bandwidth server + +- ``rtems_cbs_get_server_id`` - Get an ID of a server + +- ``rtems_cbs_get_parameters`` - Get scheduling parameters of a server + +- ``rtems_cbs_set_parameters`` - Set scheduling parameters of a server + +- ``rtems_cbs_get_execution_time`` - Get elapsed execution time + +- ``rtems_cbs_get_remaining_budget`` - Get remainig execution time + +- ``rtems_cbs_get_approved_budget`` - Get scheduler approved execution time + +Background +========== + +Constant Bandwidth Server Definitions +------------------------------------- +.. index:: CBS parameters + +.. index:: rtems_cbs_parameters + +The Constant Bandwidth Server API enables tasks to communicate with +the scheduler and indicate its scheduling parameters. The scheduler +has to be set up first (by defining ``CONFIGURE_SCHEDULER_CBS`` macro). + +The difference to a plain EDF is the presence of servers. +It is a budget aware extention of the EDF scheduler, therefore, tasks +attached to servers behave in a similar way as with EDF unless they +exceed their budget. + +The intention of servers is reservation of a certain computation +time (budget) of the processor for all subsequent periods. The structure``rtems_cbs_parameters`` determines the behavior of +a server. It contains ``deadline`` which is equal to period, +and ``budget`` which is the time the server is allowed to +spend on CPU per each period. The ratio between those two parameters +yields the maximum percentage of the CPU the server can use +(bandwidth). Moreover, thanks to this limitation the overall +utilization of CPU is under control, and the sum of bandwidths +of all servers in the system yields the overall reserved portion +of processor. The rest is still available for ordinary tasks that +are not attached to any server. + +In order to make the server effective to the executing tasks, +tasks have to be attached to the servers. The``rtems_cbs_server_id`` is a type denoting an id of a server +and ``rtems_id`` a type for id of tasks. + +Handling Periodic Tasks +----------------------- +.. index:: CBS periodic tasks + +Each task’s execution begins with a default background priority +(see the chapter Scheduling Concepts to understand the concept of +priorities in EDF). Once you decide the tasks should start periodic +execution, you have two possibilities. Either you use only the Rate +Monotonic manager which takes care of periodic behavior, or you declare +deadline and budget using the CBS API in which case these properties +are constant for all subsequent periods, unless you change them using +the CBS API again. Task now only has to indicate and end of +each period using ``rtems_rate_monotonic_period``. + +Registering a Callback Function +------------------------------- +.. index:: CBS overrun handler + +In case tasks attached to servers are not aware of their execution time +and happen to exceed it, the scheduler does not guarantee execution any +more and pulls the priority of the task to background, which would +possibly lead to immediate preemption (if there is at least one ready +task with a higher pirority). However, the task is not blocked but a +callback function is invoked. The callback function +(``rtems_cbs_budget_overrun``) might be optionally registered upon +a server creation (``rtems_cbs_create_server``). + +This enables the user to define what should happen in case of budget +overrun. There is obviously no space for huge operations because the +priority is down and not real time any more, however, you still can at +least in release resources for other tasks, restart the task or log an +error information. Since the routine is called directly from kernel, +use ``printk()`` instead of ``printf()``. + +The calling convention of the callback function is:.. index:: rtems_asr + +.. code:: c + + void overrun_handler( + rtems_cbs_server_id server_id + ); + +Limitations +----------- +.. index:: CBS limitations + +When using this scheduler you have to keep in mind several things: + +- it_limitations + +- In the current implementation it is possible to attach only + a single task to each server. + +- If you have a task attached to a server and you voluntatily + block it in the beginning of its execution, its priority will be + probably pulled to background upon unblock, thus not guaranteed + deadline any more. This is because you are effectively raising + computation time of the task. When unbocking, you should be always + sure that the ratio between remaining computation time and remaining + deadline is not higher that the utilization you have agreed with the + scheduler. + +Operations +========== + +Setting up a server +------------------- + +The directive ``rtems_cbs_create_server`` is used to create a new +server that is characterized by ``rtems_cbs_parameters``. You also +might want to register the ``rtems_cbs_budget_overrun`` callback +routine. After this step tasks can be attached to the server. The directive``rtems_cbs_set_parameters`` can change the scheduling parameters +to avoid destroying and creating a new server again. + +Attaching Task to a Server +-------------------------- + +If a task is attached to a server using ``rtems_cbs_attach_thread``, +the task’s computation time per period is limited by the server and +the deadline (period) of task is equal to deadline of the server which +means if you conclude a period using ``rate_monotonic_period``, +the length of next period is always determined by the server’s property. + +The task has a guaranteed bandwidth given by the server but should not +exceed it, otherwise the priority is pulled to background until the +start of next period and the ``rtems_cbs_budget_overrun`` callback +function is invoked. + +When attaching a task to server, the preemptability flag of the task +is raised, otherwise it would not be possible to control the execution +of the task. + +Detaching Task from a Server +---------------------------- + +The directive ``rtems_cbs_detach_thread`` is just an inverse +operation to the previous one, the task continues its execution with +the initial priority. + +Preemptability of the task is restored to the initial value. + +Examples +-------- + +The following example presents a simple common use of the API. + +You can see the initialization and cleanup call here, if there are +multiple tasks in the system, it is obvious that the initialization +should be called before creating the task. + +Notice also that in this case we decided to register an overrun handler, +instead of which there could be ``NULL``. This handler just prints +a message to terminal, what else may be done here depends on a specific +application. + +During the periodic execution, remaining budget should be watched +to avoid overrun. +.. code:: c + + void overrun_handler ( + rtems_cbs_server_id server_id + ) + { + printk( "Budget overrun, fixing the task\\n" ); + return; + } + rtems_task Tasks_Periodic( + rtems_task_argument argument + ) + { + rtems_id rmid; + rtems_cbs_server_id server_id; + rtems_cbs_parameters params; + params.deadline = 10; + params.budget = 4; + rtems_cbs_initialize(); + rtems_cbs_create_server( ¶ms, &overrun_handler, &server_id ) + rtems_cbs_attach_thread( server_id, SELF ); + rtems_rate_monotonic_create( argument, &rmid ); + while ( 1 ) { + if (rtems_rate_monotonic_period(rmid, params.deadline)==RTEMS_TIMEOUT) + break; + /* Perform some periodic action \*/ + } + rtems_rate_monotonic_delete( rmid ); + rtems_cbs_cleanup(); + exit( 1 ); + } + +Directives +========== + +This section details the Constant Bandwidth Server’s directives. +A subsection is dedicated to each of this manager’s directives +and describes the calling sequence, related constants, usage, +and status codes. + +CBS_INITIALIZE - Initialize the CBS library +------------------------------------------- +.. index:: initialize the CBS library + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_initialize + +.. code:: c + + int rtems_cbs_initialize( void ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successful initialization +``RTEMS_CBS_ERROR_NO_MEMORY`` - not enough memory for data + +**DESCRIPTION:** + +This routine initializes the library in terms of allocating necessary memory +for the servers. In case not enough memory is available in the system,``RTEMS_CBS_ERROR_NO_MEMORY`` is returned, otherwise``RTEMS_CBS_OK``. + +**NOTES:** + +Additional memory per each server is allocated upon invocation of``rtems_cbs_create_server``. + +Tasks in the system are not influenced, they still keep executing +with their initial parameters. + +CBS_CLEANUP - Cleanup the CBS library +------------------------------------- +.. index:: cleanup the CBS library + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_cleanup + +.. code:: c + + int rtems_cbs_cleanup( void ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - always successful + +**DESCRIPTION:** + +This routine detaches all tasks from their servers, destroys all servers +and returns memory back to the system. + +**NOTES:** + +All tasks continue executing with their initial priorities. + +CBS_CREATE_SERVER - Create a new bandwidth server +------------------------------------------------- +.. index:: create a new bandwidth server + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_create_server + +.. code:: c + + int rtems_cbs_create_server ( + rtems_cbs_parameters \*params, + rtems_cbs_budget_overrun budget_overrun_callback, + rtems_cbs_server_id \*server_id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successfully created +``RTEMS_CBS_ERROR_NO_MEMORY`` - not enough memory for data +``RTEMS_CBS_ERROR_FULL`` - maximum servers exceeded +``RTEMS_CBS_ERROR_INVALID_PARAMETER`` - invalid input argument + +**DESCRIPTION:** + +This routine prepares an instance of a constant bandwidth server. +The input parameter ``rtems_cbs_parameters`` specifies scheduling +parameters of the server (period and budget). If these are not valid,``RTEMS_CBS_ERROR_INVALID_PARAMETER`` is returned. +The ``budget_overrun_callback`` is an optional callback function, which is +invoked in case the server’s budget within one period is exceeded. +Output parameter ``server_id`` becomes an id of the newly created server. +If there is not enough memory, the ``RTEMS_CBS_ERROR_NO_MEMORY`` +is returned. If the maximum server count in the system is exceeded,``RTEMS_CBS_ERROR_FULL`` is returned. + +**NOTES:** + +No task execution is being influenced so far. + +CBS_ATTACH_THREAD - Attach a thread to server +--------------------------------------------- +.. index:: attach a thread to server + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_attach_thread + +.. code:: c + + int rtems_cbs_attach_thread ( + rtems_cbs_server_id server_id, + rtems_id task_id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successfully attached +``RTEMS_CBS_ERROR_FULL`` - server maximum tasks exceeded +``RTEMS_CBS_ERROR_INVALID_PARAMETER`` - invalid input argument +``RTEMS_CBS_ERROR_NOSERVER`` - server is not valid + +**DESCRIPTION:** + +Attaches a task (``task_id``) to a server (``server_id``). +The server has to be previously created. Now, the task starts +to be scheduled according to the server parameters and not +using initial priority. This implementation allows only one task +per server, if the user tries to bind another task to the same +server, ``RTEMS_CBS_ERROR_FULL`` is returned. + +**NOTES:** + +Tasks attached to servers become preemptible. + +CBS_DETACH_THREAD - Detach a thread from server +----------------------------------------------- +.. index:: detach a thread from server + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_detach_thread + +.. code:: c + + int rtems_cbs_detach_thread ( + rtems_cbs_server_id server_id, + rtems_id task_id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successfully detached +``RTEMS_CBS_ERROR_INVALID_PARAMETER`` - invalid input argument +``RTEMS_CBS_ERROR_NOSERVER`` - server is not valid + +**DESCRIPTION:** + +This directive detaches a thread from server. The task continues its +execution with initial priority. + +**NOTES:** + +The server can be reused for any other task. + +CBS_DESTROY_SERVER - Destroy a bandwidth server +----------------------------------------------- +.. index:: destroy a bandwidth server + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_destroy_server + +.. code:: c + + int rtems_cbs_destroy_server ( + rtems_cbs_server_id server_id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successfully destroyed +``RTEMS_CBS_ERROR_INVALID_PARAMETER`` - invalid input argument +``RTEMS_CBS_ERROR_NOSERVER`` - server is not valid + +**DESCRIPTION:** + +This directive destroys a server. If any task was attached to the server, +the task is detached and continues its execution according to EDF rules +with initial properties. + +**NOTES:** + +This again enables one more task to be created. + +CBS_GET_SERVER_ID - Get an ID of a server +----------------------------------------- +.. index:: get an ID of a server + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_get_server_id + +.. code:: c + + int rtems_cbs_get_server_id ( + rtems_id task_id, + rtems_cbs_server_id \*server_id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successful +``RTEMS_CBS_ERROR_NOSERVER`` - server is not valid + +**DESCRIPTION:** + +This directive returns an id of server belonging to a given task. + +CBS_GET_PARAMETERS - Get scheduling parameters of a server +---------------------------------------------------------- +.. index:: get scheduling parameters of a server + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_get_parameters + +.. code:: c + + rtems_cbs_get_parameters ( + rtems_cbs_server_id server_id, + rtems_cbs_parameters \*params + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successful +``RTEMS_CBS_ERROR_INVALID_PARAMETER`` - invalid input argument +``RTEMS_CBS_ERROR_NOSERVER`` - server is not valid + +**DESCRIPTION:** + +This directive returns a structure with current scheduling parameters +of a given server (period and execution time). + +**NOTES:** + +It makes no difference if any task is assigned or not. + +CBS_SET_PARAMETERS - Set scheduling parameters +---------------------------------------------- +.. index:: set scheduling parameters + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_set_parameters + +.. code:: c + + int rtems_cbs_set_parameters ( + rtems_cbs_server_id server_id, + rtems_cbs_parameters \*params + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successful +``RTEMS_CBS_ERROR_INVALID_PARAMETER`` - invalid input argument +``RTEMS_CBS_ERROR_NOSERVER`` - server is not valid + +**DESCRIPTION:** + +This directive sets new scheduling parameters to the server. This operation +can be performed regardless of whether a task is assigned or not. +If a task is assigned, the parameters become effective imediately, therefore it +is recommended to apply the change between two subsequent periods. + +**NOTES:** + +There is an upper limit on both period and budget equal to (2^31)-1 ticks. + +CBS_GET_EXECUTION_TIME - Get elapsed execution time +--------------------------------------------------- +.. index:: get elapsed execution time + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_get_execution_time + +.. code:: c + + int rtems_cbs_get_execution_time ( + rtems_cbs_server_id server_id, + time_t \*exec_time, + time_t \*abs_time + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successful +``RTEMS_CBS_ERROR_INVALID_PARAMETER`` - invalid input argument +``RTEMS_CBS_ERROR_NOSERVER`` - server is not valid + +**DESCRIPTION:** + +This routine returns consumed execution time (``exec_time``) of a server +during the current period. + +**NOTES:** + +Absolute time (``abs_time``) not supported now. + +CBS_GET_REMAINING_BUDGET - Get remaining execution time +------------------------------------------------------- +.. index:: get remaining execution time + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_get_remaining_budget + +.. code:: c + + int rtems_cbs_get_remaining_budget ( + rtems_cbs_server_id server_id, + time_t \*remaining_budget + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successful +``RTEMS_CBS_ERROR_INVALID_PARAMETER`` - invalid input argument +``RTEMS_CBS_ERROR_NOSERVER`` - server is not valid + +**DESCRIPTION:** + +This directive returns remaining execution time of a given server for +current period. + +**NOTES:** + +If the execution time approaches zero, the assigned task should finish +computations of the current period. + +CBS_GET_APPROVED_BUDGET - Get scheduler approved execution time +--------------------------------------------------------------- +.. index:: get scheduler approved execution time + +**CALLING SEQUENCE:** + +.. index:: rtems_cbs_get_approved_budget + +.. code:: c + + int rtems_cbs_get_approved_budget ( + rtems_cbs_server_id server_id, + time_t \*appr_budget + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_CBS_OK`` - successful +``RTEMS_CBS_ERROR_INVALID_PARAMETER`` - invalid input argument +``RTEMS_CBS_ERROR_NOSERVER`` - server is not valid + +**DESCRIPTION:** + +This directive returns server’s approved budget for subsequent periods. + +.. COMMENT: COPYRIGHT (c) 1989-2011. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Directive Status Codes +###################### + +Introduction +============ + +*``RTEMS_SUCCESSFUL`` - successful completion* + +*``RTEMS_TASK_EXITTED`` - returned from a task* + +*``RTEMS_MP_NOT_CONFIGURED`` - multiprocessing not configured* + +*``RTEMS_INVALID_NAME`` - invalid object name* + +*``RTEMS_INVALID_ID`` - invalid object id* + +*``RTEMS_TOO_MANY`` - too many* + +*``RTEMS_TIMEOUT`` - timed out waiting* + +*``RTEMS_OBJECT_WAS_DELETED`` - object was deleted while waiting* + +*``RTEMS_INVALID_SIZE`` - invalid specified size* + +*``RTEMS_INVALID_ADDRESS`` - invalid address specified* + +*``RTEMS_INVALID_NUMBER`` - number was invalid* + +*``RTEMS_NOT_DEFINED`` - item not initialized* + +*``RTEMS_RESOURCE_IN_USE`` - resources outstanding* + +*``RTEMS_UNSATISFIED`` - request not satisfied* + +*``RTEMS_INCORRECT_STATE`` - task is in wrong state* + +*``RTEMS_ALREADY_SUSPENDED`` - task already in state* + +*``RTEMS_ILLEGAL_ON_SELF`` - illegal for calling task* + +*``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` - illegal for remote object* + +*``RTEMS_CALLED_FROM_ISR`` - invalid environment* + +*``RTEMS_INVALID_PRIORITY`` - invalid task priority* + +*``RTEMS_INVALID_CLOCK`` - invalid time buffer* + +*``RTEMS_INVALID_NODE`` - invalid node id* + +*``RTEMS_NOT_CONFIGURED`` - directive not configured* + +*``RTEMS_NOT_OWNER_OF_RESOURCE`` - not owner of resource* + +*``RTEMS_NOT_IMPLEMENTED`` - directive not implemented* + +*``RTEMS_INTERNAL_ERROR`` - RTEMS inconsistency detected* + +*``RTEMS_NO_MEMORY`` - could not get enough memory* + +Directives +========== + +STATUS_TEXT - Returns the enumeration name for a status code +------------------------------------------------------------ + +**CALLING SEQUENCE:** + +.. index:: rtems_status_text + +.. code:: c + + const char \*rtems_status_text( + rtems_status_code code + ); + +**DIRECTIVE STATUS CODES** + +The status code enumeration name or "?" in case the status code is invalid. + +**DESCRIPTION:** + +Returns the enumeration name for the specified status code. + +.. COMMENT: Copyright 2015 embedded brains GmbH + +.. COMMENT: All rights reserved. + +Linker Sets +########### + +.. index:: linkersets + +Introduction +============ + +Linker sets are a flexible means to create arrays of items out of a set of +object files at link-time. For example its possible to define an item *I* +of type *T* in object file *A* and an item *J* of type *T* +in object file *B* to be a member of a linker set *S*. The linker +will then collect these two items *I* and *J* and place them in +consecutive memory locations, so that they can be accessed like a normal array +defined in one object file. The size of a linker set is defined by its begin +and end markers. A linker set may be empty. It should only contain items of +the same type. + +The following macros are provided to create, populate and use linker sets. + +- ``RTEMS_LINKER_SET_BEGIN`` - Designator of the linker set begin marker + +- ``RTEMS_LINKER_SET_END`` - Designator of the linker set end marker + +- ``RTEMS_LINKER_SET_SIZE`` - The linker set size in characters + +- ``RTEMS_LINKER_ROSET_DECLARE`` - Declares a read-only linker set + +- ``RTEMS_LINKER_ROSET`` - Defines a read-only linker set + +- ``RTEMS_LINKER_ROSET_ITEM_DECLARE`` - Declares a read-only linker set item + +- ``RTEMS_LINKER_ROSET_ITEM_REFERENCE`` - References a read-only linker set item + +- ``RTEMS_LINKER_ROSET_ITEM`` - Defines a read-only linker set item + +- ``RTEMS_LINKER_ROSET_ITEM_ORDERED`` - Defines an ordered read-only linker set item + +- ``RTEMS_LINKER_RWSET_DECLARE`` - Declares a read-write linker set + +- ``RTEMS_LINKER_RWSET`` - Defines a read-write linker set + +- ``RTEMS_LINKER_RWSET_ITEM_DECLARE`` - Declares a read-write linker set item + +- ``RTEMS_LINKER_RWSET_ITEM_REFERENCE`` - References a read-write linker set item + +- ``RTEMS_LINKER_RWSET_ITEM`` - Defines a read-write linker set item + +- ``RTEMS_LINKER_RWSET_ITEM_ORDERED`` - Defines an ordered read-write linker set item + +Background +========== + +Linker sets are used not only in RTEMS, but also for example in Linux, in +FreeBSD, for the GNU C constructor extension and for global C++ constructors. +They provide a space efficient and flexible means to initialize modules. A +linker set consists of + +- dedicated input sections for the linker (e.g. ``.ctors`` and``.ctors.*`` in the case of global constructors), + +- a begin marker (e.g. provided by ``crtbegin.o``, and + +- an end marker (e.g. provided by ``ctrend.o``). + +A module may place a certain data item into the dedicated input section. The +linker will collect all such data items in this section and creates a begin and +end marker. The initialization code can then use the begin and end markers to +find all the collected data items (e.g. pointers to initialization functions). + +In the linker command file of the GNU linker we need the following output +section descriptions. +.. code:: c + + /* To be placed in a read-only memory region \*/ + .rtemsroset : { + KEEP (\*(SORT(.rtemsroset.*))) + } + /* To be placed in a read-write memory region \*/ + .rtemsrwset : { + KEEP (\*(SORT(.rtemsrwset.*))) + } + +The ``KEEP()`` ensures that a garbage collection by the linker will not +discard the content of this section. This would normally be the case since the +linker set items are not referenced directly. The ``SORT()`` directive +sorts the input sections lexicographically. Please note the lexicographical +order of the ``.begin``, ``.content`` and ``.end`` section name parts +in the RTEMS linker sets macros which ensures that the position of the begin +and end markers are right. + +So, what is the benefit of using linker sets to initialize modules? It can be +used to initialize and include only those RTEMS managers and other components +which are used by the application. For example, in case an application uses +message queues, it must call ``rtems_message_queue_create()``. In the +module implementing this function, we can place a linker set item and register +the message queue handler constructor. Otherwise, in case the application does +not use message queues, there will be no reference to the``rtems_message_queue_create()`` function and the constructor is not +registered, thus nothing of the message queue handler will be in the final +executable. + +For an example see test program :file:`sptests/splinkersets01`. + +Directives +========== + +RTEMS_LINKER_SET_BEGIN - Designator of the linker set begin marker +------------------------------------------------------------------ + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_SET_BEGIN + +.. code:: c + + volatile type \*begin = RTEMS_LINKER_SET_BEGIN( set ); + +**DESCRIPTION:** + +This macro generates the designator of the begin marker of the linker set +identified by ``set``. The item at the begin marker address is the first +member of the linker set if it exists, e.g. the linker set is not empty. A +linker set is empty, if and only if the begin and end markers have the same +address. +The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. + +RTEMS_LINKER_SET_END - Designator of the linker set end marker +-------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_SET_END + +.. code:: c + + volatile type \*end = RTEMS_LINKER_SET_END( set ); + +**DESCRIPTION:** + +This macro generates the designator of the end marker of the linker set +identified by ``set``. The item at the end marker address is not a member +of the linker set. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. + +RTEMS_LINKER_SET_SIZE - The linker set size in characters +--------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_SET_SIZE + +.. code:: c + + size_t size = RTEMS_LINKER_SET_SIZE( set ); + +**DESCRIPTION:** + +This macro returns the size of the linker set identified by ``set`` in +characters. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. + +RTEMS_LINKER_ROSET_DECLARE - Declares a read-only linker set +------------------------------------------------------------ + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_ROSET_DECLARE + +.. code:: c + + RTEMS_LINKER_ROSET_DECLARE( set, type ); + +**DESCRIPTION:** + +This macro generates declarations for the begin and end markers of a read-only +linker set identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. + +RTEMS_LINKER_ROSET - Defines a read-only linker set +--------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_ROSET + +.. code:: c + + RTEMS_LINKER_ROSET( set, type ); + +**DESCRIPTION:** + +This macro generates definitions for the begin and end markers of a read-only +linker set identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. + +RTEMS_LINKER_ROSET_ITEM_DECLARE - Declares a read-only linker set item +---------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_ROSET_ITEM_DECLARE + +.. code:: c + + RTEMS_LINKER_ROSET_ITEM_DECLARE( set, type, item ); + +**DESCRIPTION:** + +This macro generates a declaration of an item contained in the read-only linker +set identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. The ``item`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies an item in the linker set. + +RTEMS_LINKER_ROSET_ITEM_REFERENCE - References a read-only linker set item +-------------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_ROSET_ITEM_REFERENCE + +.. code:: c + + RTEMS_LINKER_ROSET_ITEM_REFERENCE( set, type, item ); + +**DESCRIPTION:** + +This macro generates a reference to an item contained in the read-only linker set +identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. The ``item`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies an item in the linker set. + +RTEMS_LINKER_ROSET_ITEM - Defines a read-only linker set item +------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_ROSET_ITEM + +.. code:: c + + RTEMS_LINKER_ROSET_ITEM( set, type, item ); + +**DESCRIPTION:** + +This macro generates a definition of an item contained in the read-only linker set +identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. The ``item`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies an item in the linker set. + +RTEMS_LINKER_ROSET_ITEM_ORDERED - Defines an ordered read-only linker set item +------------------------------------------------------------------------------ + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_ROSET_ITEM_ORDERED + +.. code:: c + + RTEMS_LINKER_ROSET_ITEM_ORDERED( set, type, item, order ); + +**DESCRIPTION:** + +This macro generates a definition of an ordered item contained in the read-only +linker set identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. +The ``item`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies an item in the linker set. The ``order`` parameter must be a valid linker input section name part on +which macro expansion is performed. The items are lexicographically ordered +according to the ``order`` parameter within a linker set. Ordered items are +placed before unordered items in the linker set. + +**NOTES:** + +To be resilient to typos in the order parameter, it is recommended to use the +following construct in macros defining items for a particular linker set (see +enum in ``XYZ_ITEM()``). +.. code:: c + + #include + typedef struct { + int foo; + } xyz_item; + /* The XYZ-order defines \*/ + #define XYZ_ORDER_FIRST 0x00001000 + #define XYZ_ORDER_AND_SO_ON 0x00002000 + /* Defines an ordered XYZ-item \*/ + #define XYZ_ITEM( item, order ) \\ + enum { xyz_##item = order - order }; \\ + RTEMS_LINKER_ROSET_ITEM_ORDERED( \\ + xyz, const xyz_item \*, item, order \\ + ) = { &item } + /* Example item \*/ + static const xyz_item some_item = { 123 }; + XYZ_ITEM( some_item, XYZ_ORDER_FIRST ); + +RTEMS_LINKER_RWSET_DECLARE - Declares a read-write linker set +------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_RWSET_DECLARE + +.. code:: c + + RTEMS_LINKER_RWSET_DECLARE( set, type ); + +**DESCRIPTION:** + +This macro generates declarations for the begin and end markers of a read-write +linker set identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. + +RTEMS_LINKER_RWSET - Defines a read-write linker set +---------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_RWSET + +.. code:: c + + RTEMS_LINKER_RWSET( set, type ); + +**DESCRIPTION:** + +This macro generates definitions for the begin and end markers of a read-write +linker set identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. + +RTEMS_LINKER_RWSET_ITEM_DECLARE - Declares a read-write linker set item +----------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_RWSET_ITEM_DECLARE + +.. code:: c + + RTEMS_LINKER_RWSET_ITEM_DECLARE( set, type, item ); + +**DESCRIPTION:** + +This macro generates a declaration of an item contained in the read-write linker +set identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. The ``item`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies an item in the linker set. + +RTEMS_LINKER_RWSET_ITEM_REFERENCE - References a read-write linker set item +--------------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_RWSET_ITEM_REFERENCE + +.. code:: c + + RTEMS_LINKER_RWSET_ITEM_REFERENCE( set, type, item ); + +**DESCRIPTION:** + +This macro generates a reference to an item contained in the read-write linker set +identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. The ``item`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies an item in the linker set. + +RTEMS_LINKER_RWSET_ITEM - Defines a read-write linker set item +-------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_RWSET_ITEM + +.. code:: c + + RTEMS_LINKER_RWSET_ITEM( set, type, item ); + +**DESCRIPTION:** + +This macro generates a definition of an item contained in the read-write linker set +identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. The ``item`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies an item in the linker set. + +RTEMS_LINKER_RWSET_ITEM_ORDERED - Defines an ordered read-write linker set item +------------------------------------------------------------------------------- + +**CALLING SEQUENCE:** + +.. index:: RTEMS_LINKER_RWSET_ITEM_ORDERED + +.. code:: c + + RTEMS_LINKER_RWSET_ITEM_ORDERED( set, type, item, order ); + +**DESCRIPTION:** + +This macro generates a definition of an ordered item contained in the read-write +linker set identified by ``set``. The ``set`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies the linker set. The ``type`` parameter defines the type of the linker set items. The type +must be the same for all macro invocations of a particular linker set. +The ``item`` parameter itself must be a valid C designator on which no macro +expansion is performed. It uniquely identifies an item in the linker set. The ``order`` parameter must be a valid linker input section name part on +which macro expansion is performed. The items are lexicographically ordered +according to the ``order`` parameter within a linker set. Ordered items are +placed before unordered items in the linker set. + +**NOTES:** + +To be resilient to typos in the order parameter, it is recommended to use the +following construct in macros defining items for a particular linker set (see +enum in ``XYZ_ITEM()``). +.. code:: c + + #include + typedef struct { + int foo; + } xyz_item; + /* The XYZ-order defines \*/ + #define XYZ_ORDER_FIRST 0x00001000 + #define XYZ_ORDER_AND_SO_ON 0x00002000 + /* Defines an ordered XYZ-item \*/ + #define XYZ_ITEM( item, order ) \\ + enum { xyz_##item = order - order }; \\ + RTEMS_LINKER_RWSET_ITEM_ORDERED( \\ + xyz, const xyz_item \*, item, order \\ + ) = { &item } + /* Example item \*/ + static const xyz_item some_item = { 123 }; + XYZ_ITEM( some_item, XYZ_ORDER_FIRST ); + +.. COMMENT: COPYRIGHT (c) 1989-2014. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Example Application +################### + +.. code:: c + + /* + * This file contains an example of a simple RTEMS + * application. It instantiates the RTEMS Configuration + * Information using confdef.h and contains two tasks: + * a user initialization task and a simple task. + \*/ + #include + rtems_task user_application(rtems_task_argument argument); + rtems_task init_task( + rtems_task_argument ignored + ) + { + rtems_id tid; + rtems_status_code status; + rtems_name name; + name = rtems_build_name( 'A', 'P', 'P', '1' ) + status = rtems_task_create( + name, 1, RTEMS_MINIMUM_STACK_SIZE, + RTEMS_NO_PREEMPT, RTEMS_FLOATING_POINT, &tid + ); + if ( status != RTEMS_STATUS_SUCCESSFUL ) { + printf( "rtems_task_create failed with status of %d.\\n", status ); + exit( 1 ); + } + status = rtems_task_start( tid, user_application, 0 ); + if ( status != RTEMS_STATUS_SUCCESSFUL ) { + printf( "rtems_task_start failed with status of %d.\\n", status ); + exit( 1 ); + } + status = rtems_task_delete( SELF ); /* should not return \*/ + printf( "rtems_task_delete returned with status of %d.\\n", status ); + exit( 1 ); + } + rtems_task user_application(rtems_task_argument argument) + { + /* application specific initialization goes here \*/ + while ( 1 ) { /* infinite loop \*/ + /* APPLICATION CODE GOES HERE + * + * This code will typically include at least one + * directive which causes the calling task to + * give up the processor. + \*/ + } + } + /* The Console Driver supplies Standard I/O. \*/ + #define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER + /* The Clock Driver supplies the clock tick. \*/ + #define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER + #define CONFIGURE_MAXIMUM_TASKS 2 + #define CONFIGURE_INIT_TASK_NAME rtems_build_name( 'E', 'X', 'A', 'M' ) + #define CONFIGURE_RTEMS_INIT_TASKS_TABLE + #define CONFIGURE_INIT + #include + +.. COMMENT: COPYRIGHT (c) 1989-2011. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Glossary +######## + +:dfn:`active` + A term used to describe an object + which has been created by an application. + +:dfn:`aperiodic task` + A task which must execute only at + irregular intervals and has only a soft deadline. + +:dfn:`application` + In this document, software which makes + use of RTEMS. + +:dfn:`ASR` + see Asynchronous Signal Routine. + +:dfn:`asynchronous` + Not related in order or timing to + other occurrences in the system. + +:dfn:`Asynchronous Signal Routine` + Similar to a hardware + interrupt except that it is associated with a task and is run in + the context of a task. The directives provided by the signal + manager are used to service signals. + +:dfn:`atomic operations` + Atomic operations are defined in terms of *ISO/IEC 9899:2011*. + +:dfn:`awakened` + A term used to describe a task that has + been unblocked and may be scheduled to the CPU. + +:dfn:`big endian` + A data representation scheme in which + the bytes composing a numeric value are arranged such that the + most significant byte is at the lowest address. + +:dfn:`bit-mapped` + A data encoding scheme in which each bit + in a variable is used to represent something different. This + makes for compact data representation. + +:dfn:`block` + A physically contiguous area of memory. + +:dfn:`blocked task` + The task state entered by a task which has been previously started and cannot + continue execution until the reason for waiting has been satisfied. Blocked + tasks are not an element of the set of ready tasks of a scheduler instance. + +:dfn:`broadcast` + To simultaneously send a message to a + logical set of destinations. + +:dfn:`BSP` + see Board Support Package. + +:dfn:`Board Support Package` + A collection of device + initialization and control routines specific to a particular + type of board or collection of boards. + +:dfn:`buffer` + A fixed length block of memory allocated + from a partition. + +:dfn:`calling convention` + The processor and compiler + dependent rules which define the mechanism used to invoke + subroutines in a high-level language. These rules define the + passing of arguments, the call and return mechanism, and the + register set which must be preserved. + +:dfn:`Central Processing Unit` + This term is equivalent to + the terms processor and microprocessor. + +:dfn:`chain` + A data structure which allows for efficient + dynamic addition and removal of elements. It differs from an + array in that it is not limited to a predefined size. + +:dfn:`cluster` + We have clustered scheduling in case the set of processors of a system is + partitioned into non-empty pairwise disjoint subsets. These subsets are called:dfn:`clusters`. Clusters with a cardinality of one are partitions. Each + cluster is owned by exactly one scheduler instance. + +:dfn:`coalesce` + The process of merging adjacent holes into + a single larger hole. Sometimes this process is referred to as + garbage collection. + +:dfn:`Configuration Table` + A table which contains + information used to tailor RTEMS for a particular application. + +:dfn:`context` + All of the processor registers and + operating system data structures associated with a task. + +:dfn:`context switch` + Alternate term for task switch. + Taking control of the processor from one task and transferring + it to another task. + +:dfn:`control block` + A data structure used by the + executive to define and control an object. + +:dfn:`core` + When used in this manual, this term refers to + the internal executive utility functions. In the interest of + application portability, the core of the executive should not be + used directly by applications. + +:dfn:`CPU` + An acronym for Central Processing Unit. + +:dfn:`critical section` + A section of code which must be + executed indivisibly. + +:dfn:`CRT` + An acronym for Cathode Ray Tube. Normally used + in reference to the man-machine interface. + +:dfn:`deadline` + A fixed time limit by which a task must + have completed a set of actions. Beyond this point, the results + are of reduced value and may even be considered useless or + harmful. + +:dfn:`device` + A peripheral used by the application that + requires special operation software. See also device driver. + +:dfn:`device driver` + Control software for special + peripheral devices used by the application. + +:dfn:`directives` + RTEMS’ provided routines that provide + support mechanisms for real-time applications. + +:dfn:`dispatch` + The act of loading a task’s context onto + the CPU and transferring control of the CPU to that task. + +:dfn:`dormant` + The state entered by a task after it is + created and before it has been started. + +:dfn:`Device Driver Table` + A table which contains the + entry points for each of the configured device drivers. + +:dfn:`dual-ported` + A term used to describe memory which + can be accessed at two different addresses. + +:dfn:`embedded` + An application that is delivered as a + hidden part of a larger system. For example, the software in a + fuel-injection control system is an embedded application found + in many late-model automobiles. + +:dfn:`envelope` + A buffer provided by the MPCI layer to + RTEMS which is used to pass messages between nodes in a + multiprocessor system. It typically contains routing + information needed by the MPCI. The contents of an envelope are + referred to as a packet. + +:dfn:`entry point` + The address at which a function or task + begins to execute. In C, the entry point of a function is the + function’s name. + +:dfn:`events` + A method for task communication and + synchronization. The directives provided by the event manager + are used to service events. + +:dfn:`exception` + A synonym for interrupt. + +:dfn:`executing task` + The task state entered by a task after it has been given control of the + processor. On SMP configurations a task may be registered as executing on more + than one processor for short time frames during task migration. Blocked tasks + can be executing until they issue a thread dispatch. + +:dfn:`executive` + In this document, this term is used to + referred to RTEMS. Commonly, an executive is a small real-time + operating system used in embedded systems. + +:dfn:`exported` + An object known by all nodes in a + multiprocessor system. An object created with the GLOBAL + attribute will be exported. + +:dfn:`external address` + The address used to access + dual-ported memory by all the nodes in a system which do not own + the memory. + +:dfn:`FIFO` + An acronym for First In First Out. + +:dfn:`First In First Out` + A discipline for manipulating entries in a data structure. + +:dfn:`floating point coprocessor` + A component used in + computer systems to enhance performance in mathematically + intensive situations. It is typically viewed as a logical + extension of the primary processor. + +:dfn:`freed` + A resource that has been released by the + application to RTEMS. + +:dfn:`Giant lock` + The :dfn:`Giant lock` is a recursive SMP lock protecting most parts of the + operating system state. Virtually every operating system service must acquire + and release the Giant lock during its operation. + +:dfn:`global` + An object that has been created with the + GLOBAL attribute and exported to all nodes in a multiprocessor + system. + +:dfn:`handler` + The equivalent of a manager, except that it + is internal to RTEMS and forms part of the core. A handler is a + collection of routines which provide a related set of functions. + For example, there is a handler used by RTEMS to manage all + objects. + +:dfn:`hard real-time system` + A real-time system in which a + missed deadline causes the worked performed to have no value or + to result in a catastrophic effect on the integrity of the + system. + +:dfn:`heap` + A data structure used to dynamically allocate + and deallocate variable sized blocks of memory. + +:dfn:`heir task` + A task is an :dfn:`heir` if it is registered as an heir in a processor of the + system. A task can be the heir on at most one processor in the system. In + case the executing and heir tasks differ on a processor and a thread dispatch + is marked as necessary, then the next thread dispatch will make the heir task + the executing task. + +:dfn:`heterogeneous` + A multiprocessor computer system composed of dissimilar processors. + +:dfn:`homogeneous` + A multiprocessor computer system composed of a single type of processor. + +:dfn:`ID` + An RTEMS assigned identification tag used to + access an active object. + +:dfn:`IDLE task` + A special low priority task which assumes + control of the CPU when no other task is able to execute. + +:dfn:`interface` + A specification of the methodology used + to connect multiple independent subsystems. + +:dfn:`internal address` + The address used to access + dual-ported memory by the node which owns the memory. + +:dfn:`interrupt` + A hardware facility that causes the CPU + to suspend execution, save its status, and transfer control to a + specific location. + +:dfn:`interrupt level` + A mask used to by the CPU to + determine which pending interrupts should be serviced. If a + pending interrupt is below the current interrupt level, then the + CPU does not recognize that interrupt. + +:dfn:`Interrupt Service Routine` + An ISR is invoked by the + CPU to process a pending interrupt. + +:dfn:`I/O` + An acronym for Input/Output. + +:dfn:`ISR` + An acronym for Interrupt Service Routine. + +:dfn:`kernel` + In this document, this term is used as a + synonym for executive. + +:dfn:`list` + A data structure which allows for dynamic + addition and removal of entries. It is not statically limited + to a particular size. + +:dfn:`little endian` + A data representation scheme in which + the bytes composing a numeric value are arranged such that the + least significant byte is at the lowest address. + +:dfn:`local` + An object which was created with the LOCAL + attribute and is accessible only on the node it was created and + resides upon. In a single processor configuration, all objects + are local. + +:dfn:`local operation` + The manipulation of an object which + resides on the same node as the calling task. + +:dfn:`logical address` + An address used by an application. + In a system without memory management, logical addresses will + equal physical addresses. + +:dfn:`loosely-coupled` + A multiprocessor configuration + where shared memory is not used for communication. + +:dfn:`major number` + The index of a device driver in the + Device Driver Table. + +:dfn:`manager` + A group of related RTEMS’ directives which + provide access and control over resources. + +:dfn:`memory pool` + Used interchangeably with heap. + +:dfn:`message` + A sixteen byte entity used to communicate + between tasks. Messages are sent to message queues and stored + in message buffers. + +:dfn:`message buffer` + A block of memory used to store + messages. + +:dfn:`message queue` + An RTEMS object used to synchronize + and communicate between tasks by transporting messages between + sending and receiving tasks. + +:dfn:`Message Queue Control Block` + A data structure associated with each message queue used by RTEMS + to manage that message queue. + +:dfn:`minor number` + A numeric value passed to a device + driver, the exact usage of which is driver dependent. + +:dfn:`mode` + An entry in a task’s control block that is + used to determine if the task allows preemption, timeslicing, + processing of signals, and the interrupt disable level used by + the task. + +:dfn:`MPCI` + An acronym for Multiprocessor Communications + Interface Layer. + +:dfn:`multiprocessing` + The simultaneous execution of two + or more processes by a multiple processor computer system. + +:dfn:`multiprocessor` + A computer with multiple CPUs + available for executing applications. + +:dfn:`Multiprocessor Communications Interface Layer` + A set + of user-provided routines which enable the nodes in a + multiprocessor system to communicate with one another. + +:dfn:`Multiprocessor Configuration Table` + The data structure defining the characteristics of the multiprocessor + target system with which RTEMS will communicate. + +:dfn:`multitasking` + The alternation of execution amongst a + group of processes on a single CPU. A scheduling algorithm is + used to determine which process executes at which time. + +:dfn:`mutual exclusion` + A term used to describe the act of + preventing other tasks from accessing a resource simultaneously. + +:dfn:`nested` + A term used to describe an ASR that occurs + during another ASR or an ISR that occurs during another ISR. + +:dfn:`node` + A term used to reference a processor running + RTEMS in a multiprocessor system. + +:dfn:`non-existent` + The state occupied by an uncreated or + deleted task. + +:dfn:`numeric coprocessor` + A component used in computer + systems to enhance performance in mathematically intensive + situations. It is typically viewed as a logical extension of + the primary processor. + +:dfn:`object` + In this document, this term is used to refer + collectively to tasks, timers, message queues, partitions, + regions, semaphores, ports, and rate monotonic periods. All + RTEMS objects have IDs and user-assigned names. + +:dfn:`object-oriented` + A term used to describe systems + with common mechanisms for utilizing a variety of entities. + Object-oriented systems shield the application from + implementation details. + +:dfn:`operating system` + The software which controls all + the computer’s resources and provides the base upon which + application programs can be written. + +:dfn:`overhead` + The portion of the CPUs processing power + consumed by the operating system. + +:dfn:`packet` + A buffer which contains the messages passed + between nodes in a multiprocessor system. A packet is the + contents of an envelope. + +:dfn:`partition` + An RTEMS object which is used to allocate + and deallocate fixed size blocks of memory from an dynamically + specified area of memory. + +:dfn:`partition` + Clusters with a cardinality of one are :dfn:`partitions`. + +:dfn:`Partition Control Block` + A data structure associated + with each partition used by RTEMS to manage that partition. + +:dfn:`pending` + A term used to describe a task blocked + waiting for an event, message, semaphore, or signal. + +:dfn:`periodic task` + A task which must execute at regular + intervals and comply with a hard deadline. + +:dfn:`physical address` + The actual hardware address of a + resource. + +:dfn:`poll` + A mechanism used to determine if an event has + occurred by periodically checking for a particular status. + Typical events include arrival of data, completion of an action, + and errors. + +:dfn:`pool` + A collection from which resources are + allocated. + +:dfn:`portability` + A term used to describe the ease with + which software can be rehosted on another computer. + +:dfn:`posting` + The act of sending an event, message, + semaphore, or signal to a task. + +:dfn:`preempt` + The act of forcing a task to relinquish the + processor and dispatching to another task. + +:dfn:`priority` + A mechanism used to represent the relative + importance of an element in a set of items. RTEMS uses priority + to determine which task should execute. + +:dfn:`priority boosting` + A simple approach to extend the priority inheritance protocol for clustered + scheduling is :dfn:`priority boosting`. In case a mutex is owned by a task of + another cluster, then the priority of the owner task is raised to an + artificially high priority, the pseudo-interrupt priority. + +:dfn:`priority inheritance` + An algorithm that calls for + the lower priority task holding a resource to have its priority + increased to that of the highest priority task blocked waiting + for that resource. This avoids the problem of priority + inversion. + +:dfn:`priority inversion` + A form of indefinite + postponement which occurs when a high priority tasks requests + access to shared resource currently allocated to low priority + task. The high priority task must block until the low priority + task releases the resource. + +:dfn:`processor utilization` + The percentage of processor + time used by a task or a set of tasks. + +:dfn:`proxy` + An RTEMS control structure used to represent, + on a remote node, a task which must block as part of a remote + operation. + +:dfn:`Proxy Control Block` + A data structure associated + with each proxy used by RTEMS to manage that proxy. + +:dfn:`PTCB` + An acronym for Partition Control Block. + +:dfn:`PXCB` + An acronym for Proxy Control Block. + +:dfn:`quantum` + The application defined unit of time in + which the processor is allocated. + +:dfn:`queue` + Alternate term for message queue. + +:dfn:`QCB` + An acronym for Message Queue Control Block. + +:dfn:`ready task` + A task occupies this state when it is available to be given control of a + processor. A ready task has no processor assigned. The scheduler decided that + other tasks are currently more important. A task that is ready to execute and + has a processor assigned is called scheduled. + +:dfn:`real-time` + A term used to describe systems which are + characterized by requiring deterministic response times to + external stimuli. The external stimuli require that the + response occur at a precise time or the response is incorrect. + +:dfn:`reentrant` + A term used to describe routines which do + not modify themselves or global variables. + +:dfn:`region` + An RTEMS object which is used to allocate + and deallocate variable size blocks of memory from a dynamically + specified area of memory. + +:dfn:`Region Control Block` + A data structure associated + with each region used by RTEMS to manage that region. + +:dfn:`registers` + Registers are locations physically + located within a component, typically used for device control or + general purpose storage. + +:dfn:`remote` + Any object that does not reside on the local + node. + +:dfn:`remote operation` + The manipulation of an object + which does not reside on the same node as the calling task. + +:dfn:`return code` + Also known as error code or return + value. + +:dfn:`resource` + A hardware or software entity to which + access must be controlled. + +:dfn:`resume` + Removing a task from the suspend state. If + the task’s state is ready following a call to the ``rtems_task_resume`` + directive, then the task is available for scheduling. + +:dfn:`return code` + A value returned by RTEMS directives to + indicate the completion status of the directive. + +:dfn:`RNCB` + An acronym for Region Control Block. + +:dfn:`round-robin` + A task scheduling discipline in which + tasks of equal priority are executed in the order in which they + are made ready. + +:dfn:`RS-232` + A standard for serial communications. + +:dfn:`running` + The state of a rate monotonic timer while + it is being used to delineate a period. The timer exits this + state by either expiring or being canceled. + +:dfn:`schedulable` + A set of tasks which can be guaranteed + to meet their deadlines based upon a specific scheduling + algorithm. + +:dfn:`schedule` + The process of choosing which task should + next enter the executing state. + +:dfn:`scheduled task` + A task is :dfn:`scheduled` if it is allowed to execute and has a processor + assigned. Such a task executes currently on a processor or is about to start + execution. A task about to start execution it is an heir task on exactly one + processor in the system. + +:dfn:`scheduler` + A :dfn:`scheduler` or :dfn:`scheduling algorithm` allocates processors to a + subset of its set of ready tasks. So it manages access to the processor + resource. Various algorithms exist to choose the tasks allowed to use a + processor out of the set of ready tasks. One method is to assign each task a + priority number and assign the tasks with the lowest priority number to one + processor of the set of processors owned by a scheduler instance. + +:dfn:`scheduler instance` + A :dfn:`scheduler instance` is a scheduling algorithm with a corresponding + context to store its internal state. Each processor in the system is owned by + at most one scheduler instance. The processor to scheduler instance assignment + is determined at application configuration time. See `Configuring a System`_. + +:dfn:`segments` + Variable sized memory blocks allocated + from a region. + +:dfn:`semaphore` + An RTEMS object which is used to + synchronize tasks and provide mutually exclusive access to + resources. + +:dfn:`Semaphore Control Block` + A data structure associated + with each semaphore used by RTEMS to manage that semaphore. + +:dfn:`shared memory` + Memory which is accessible by + multiple nodes in a multiprocessor system. + +:dfn:`signal` + An RTEMS provided mechanism to communicate + asynchronously with a task. Upon reception of a signal, the ASR + of the receiving task will be invoked. + +:dfn:`signal set` + A thirty-two bit entity which is used to + represent a task’s collection of pending signals and the signals + sent to a task. + +:dfn:`SMCB` + An acronym for Semaphore Control Block. + +:dfn:`SMP locks` + The :dfn:`SMP locks` ensure mutual exclusion on the lowest level and are a + replacement for the sections of disabled interrupts. Interrupts are usually + disabled while holding an SMP lock. They are implemented using atomic + operations. Currently a ticket lock is used in RTEMS. + +:dfn:`SMP barriers` + The :dfn:`SMP barriers` ensure that a defined set of independent threads of + execution on a set of processors reaches a common synchronization point in + time. They are implemented using atomic operations. Currently a sense barrier + is used in RTEMS. + +:dfn:`soft real-time system` + A real-time system in which a + missed deadline does not compromise the integrity of the system. + +:dfn:`sporadic task` + A task which executes at irregular + intervals and must comply with a hard deadline. A minimum + period of time between successive iterations of the task can be + guaranteed. + +:dfn:`stack` + A data structure that is managed using a Last + In First Out (LIFO) discipline. Each task has a stack + associated with it which is used to store return information + and local variables. + +:dfn:`status code` + Also known as error code or return + value. + +:dfn:`suspend` + A term used to describe a task that is not + competing for the CPU because it has had a ``rtems_task_suspend`` directive. + +:dfn:`synchronous` + Related in order or timing to other + occurrences in the system. + +:dfn:`system call` + In this document, this is used as an + alternate term for directive. + +:dfn:`target` + The system on which the application will + ultimately execute. + +:dfn:`task` + A logically complete thread of execution. It consists normally of a set of + registers and a stack. The terms :dfn:`task` and :dfn:`thread` are synonym in + RTEMS. The scheduler assigns processors to a subset of the ready tasks. + +:dfn:`Task Control Block` + A data structure associated with + each task used by RTEMS to manage that task. + +:dfn:`task migration` + :dfn:`Task migration` happens in case a task stops execution on one processor + and resumes execution on another processor. + +:dfn:`task processor affinity` + The set of processors on which a task is allowed to execute. + +:dfn:`task switch` + Alternate terminology for context + switch. Taking control of the processor from one task and given + to another. + +:dfn:`TCB` + An acronym for Task Control Block. + +:dfn:`thread dispatch` + The :dfn:`thread dispatch` transfers control of the processor from the currently + executing thread to the heir thread of the processor. + +:dfn:`tick` + The basic unit of time used by RTEMS. It is a + user-configurable number of microseconds. The current tick + expires when the ``rtems_clock_tick`` + directive is invoked. + +:dfn:`tightly-coupled` + A multiprocessor configuration + system which communicates via shared memory. + +:dfn:`timeout` + An argument provided to a number of + directives which determines the maximum length of time an + application task is willing to wait to acquire the resource if + it is not immediately available. + +:dfn:`timer` + An RTEMS object used to invoke subprograms at + a later time. + +:dfn:`Timer Control Block` + A data structure associated + with each timer used by RTEMS to manage that timer. + +:dfn:`timeslicing` + A task scheduling discipline in which + tasks of equal priority are executed for a specific period of + time before being preempted by another task. + +:dfn:`timeslice` + The application defined unit of time in + which the processor is allocated. + +:dfn:`TMCB` + An acronym for Timer Control Block. + +:dfn:`transient overload` + A temporary rise in system + activity which may cause deadlines to be missed. Rate Monotonic + Scheduling can be used to determine if all deadlines will be met + under transient overload. + +:dfn:`user extensions` + Software routines provided by the + application to enhance the functionality of RTEMS. + +:dfn:`User Extension Table` + A table which contains the + entry points for each user extensions. + +:dfn:`User Initialization Tasks Table` + A table which + contains the information needed to create and start each of the + user initialization tasks. + +:dfn:`user-provided` + Alternate term for user-supplied. + This term is used to designate any software routines which must + be written by the application designer. + +:dfn:`user-supplied` + Alternate term for user-provided. + This term is used to designate any software routines which must + be written by the application designer. + +:dfn:`vector` + Memory pointers used by the processor to + fetch the address of routines which will handle various + exceptions and interrupts. + +:dfn:`wait queue` + The list of tasks blocked pending the + release of a particular resource. Message queues, regions, and + semaphores have a wait queue associated with them. + +:dfn:`yield` + When a task voluntarily releases control of the processor. + +Command and Variable Index +########################## + +.. COMMENT: There are currently no Command and Variable Index entries. + +Concept Index +############# + +.. COMMENT: There are currently no Concept Index entries. + -- cgit v1.2.3