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diff --git a/cpukit/include/rtems/rtems/mainpage.h b/cpukit/include/rtems/rtems/mainpage.h deleted file mode 100644 index 05bae7fe70..0000000000 --- a/cpukit/include/rtems/rtems/mainpage.h +++ /dev/null @@ -1,929 +0,0 @@ -/** - * @file - * - * This file exists to provide a top level description of RTEMS for Doxygen. - */ - -/* - * COPYRIGHT (c) 1989-2014. - * On-Line Applications Research Corporation (OAR). - * - * The license and distribution terms for this file may be - * found in the file LICENSE in this distribution or at - * http://www.rtems.org/license/LICENSE. - */ - -/** - * @mainpage - * - * The RTEMS real-time operating systems is a layered system with each of the - * public APIs implemented in terms of a common foundation layer called the - * SuperCore. This is the Doxygen generated documentation for the RTEMS CPU - * Kit including the Classic API, POSIX API and SuperCore. - */ - -/** - * @page RTEMSPreface RTEMS History and Introduction - * - * 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 - * - ARM - * - Freescale (formerly Motorola) MC68xxx - * - Freescale (formerly Motorola) MC683xx - * - Freescale (formerly Motorola) ColdFire - * - Intel i386 and above - * - Lattice Semiconductor LM32 - * - MIPS - * - PowerPC - * - Renesas (formerly Hitachi) SuperH - * - Renesas (formerly Hitachi) H8/300 - * - SPARC - * - Texas Instruments C3x/C4x - * - UNIX - * - * 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. - */ - -/** - * @page RTEMSOverview RTEMS Overview - * - * @section RTEMSOverviewSecIntroduction 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. - * - * @section RTEMSOverviewSecRealtimeApplicationSystems 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. - * - * @section RTEMSOverviewSecRealtimeExecutive 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. - * - * @section RTEMSOverviewSecApplicationArchitecture 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. - * - * @todo Image RTEMS Application Architecture - * - * 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. - * - * @section RTEMSOverviewSecInternalArchitecture 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: - * - * @todo Image RTEMS Architecture - * - * 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 - * - * @section RTEMSOverviewSecUserCustomization User Customization and Extensibility - * - * As 32-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 32-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. - * - * @section RTEMSOverviewSecPortability 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. - * - * @section RTEMSOverviewSecMemoryRequirements 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 filesystems, 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 Determining Memory - * Requirements for more details. - * - * @todo Link to Configuring a SystemDetermining Memory Requirements - * - * 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. - * - * @section RTEMSOverviewSecAudience 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. - */ - -/** - * @addtogroup RTEMSAPIClassic - * - * 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. - * - * @section ClassicRTEMSSecObjects 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. - * - * @subsection ClassicRTEMSSubSecObjectNames Object Names - * - * An object name is an unsigned 32-bit entity associated with the - * object by the user. The data type @ref rtems_name is used to store object names. - * - * 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 - * rtems_name my_name = rtems_build_name('L', 'I', 'T', 'E'); - * @endcode - * - * 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. - * - * 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. - * - * @subsection ClassicRTEMSSubSecObjectIdentifiers Object Identifiers - * - * 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 32-bit - * format which is used for most of the supported architectures and supports - * multiprocessor configurations. There is also a simpler 16-bit format which - * is appropriate for smaller target architectures and does not support - * multiprocessor configurations. - * - * @subsubsection ClassicRTEMSSubSec32BitObjectIdentifierFormat 32-Bit Object Identifier Format - * - * The 32-bit format for an object ID is composed of four parts: API, - * object class, node, and index. The data type @ref rtems_id is used to store - * object IDs. - * - * <table> - * <tr> - * <th>Bits</th> - * <td>31</td><td>30</td><td>29</td><td>28</td><td>27</td><td>26</td><td>25</td><td>24</td> - * <td>23</td><td>22</td><td>21</td><td>20</td><td>19</td><td>18</td><td>17</td><td>16</td> - * <td>15</td><td>14</td><td>13</td><td>12</td><td>11</td><td>10</td><td>09</td><td>08</td> - * <td>07</td><td>06</td><td>05</td><td>04</td><td>03</td><td>02</td><td>01</td><td>00</td> - * </tr> - * <tr> - * <th>Contents</th> - * <td colspan=5>Class</td><td colspan=3>API</td><td colspan=8>Node</td><td colspan=16>Object Index</td> - * </tr> - * </table> - * - * 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 16-bits form an identifier within a particular object type. - * This identifier, called the object index, ranges in value from one to the - * maximum number of objects configured for this object type. - * - * @subsubsection ClassicRTEMSSubSec16BitObjectIdentifierFormat 16-Bit Object Identifier Format - * - * The 16-bit format for an object ID is composed of three parts: API, object - * class, and index. The data type @ref rtems_id is used to store object IDs. - * - * <table> - * <tr> - * <th>Bits</th> - * <td>15</td><td>14</td><td>13</td><td>12</td><td>11</td><td>10</td><td>09</td><td>08</td> - * <td>07</td><td>06</td><td>05</td><td>04</td><td>03</td><td>02</td><td>01</td><td>00</td> - * </tr> - * <tr> - * <th>Contents</th> - * <td colspan=5>Class</td><td colspan=3>API</td><td colspan=8>Object Index</td> - * </tr> - * </table> - * - * The 16-bit format is designed to be as similar as possible to the 32-bit - * format. The differences are limited to the elimination of the node field - * and reduction of the index field from 16-bits to 8-bits. Thus the 16-bit - * format only supports up to 255 object instances per API/Class combination - * and single processor systems. As this format is typically utilized by 16-bit - * processors with limited address space, this is more than enough object - * instances. - * - * @subsection ClassicRTEMSSubSecObjectIdentiferDescription Object Identifer 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: - * - * - rtems_object_id_get_api() - * - rtems_object_id_get_class() - * - rtems_object_id_get_node() - * - rtems_object_id_get_index() - * - * 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. - * - * @section ClassicRTEMSSecComSync 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, and - * - 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: - * - * - @ref ClassicSem - * - @ref ClassicMessageQueue - * - @ref ClassicEvent - * - @ref ClassicSignal - * - * 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. - * - * @section ClassicRTEMSSecTime 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. - * - * 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 @ref 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 @ref rtems_time_of_day is used to specify - * calendar time in RTEMS services. See Clock Manager Time and Date Data - * Structures. - * - * @todo Link to Clock Manager Time and Date Data Structures - * - * 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. - * - * @section ClassicRTEMSSecMemoryManagement 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: - * - * - @ref ClassicRegion - * - @ref ClassicPart - * - @ref ClassicDPMEM - * - * 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. - */ - -/** - * @addtogroup RTEMSAPIClassicTasks - * - * @section ClassicTasksSecTaskDefinition 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). - * - * @section ClassicTasksSecTaskControlBlock 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. - * - * @section ClassicTasksSecTaskStates 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. - * - * @section ClassicTasksSecTaskPriority 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. - * - * @section ClassicTasksSecTaskMode 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. - * - * The preemption component allows a task to determine when control of the - * processor is relinquished. If preemption is disabled (@c - * 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 (@c 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. - * - * 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 (@c 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 (@c - * RTEMS_NO_TIMESLICE), then the task will be allowed to - * execute until a task of higher priority is made ready. If @c - * 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 (@c RTEMS_ASR), then signals sent to the task will be processed - * the next time the task executes. If signal processing is disabled (@c - * 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. - * - * The interrupt level component is used to determine which interrupts will be - * enabled when the task is executing. @c RTEMS_INTERRUPT_LEVEL(n) specifies - * that the task will execute at interrupt level n. - * - * - @ref RTEMS_PREEMPT - enable preemption (default) - * - @ref RTEMS_NO_PREEMPT - disable preemption - * - @ref RTEMS_NO_TIMESLICE - disable timeslicing (default) - * - @ref RTEMS_TIMESLICE - enable timeslicing - * - @ref RTEMS_ASR - enable ASR processing (default) - * - @ref RTEMS_NO_ASR - disable ASR processing - * - @ref RTEMS_INTERRUPT_LEVEL(0) - enable all interrupts (default) - * - @ref RTEMS_INTERRUPT_LEVEL(n) - execute at interrupt level n - * - * The set of default modes may be selected by specifying the @ref - * RTEMS_DEFAULT_MODES constant. - * - * @section ClassicTasksSecAccessingTaskArguments Accessing Task Arguments - * - * 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: - * - * @code - * rtems_task user_task( - * rtems_task_argument argument - * ); - * @endcode - * - * Application tasks requiring more information may view this single argument - * as an index into an array of parameter blocks. - * - * @section ClassicTasksSecFloatingPointConsiderations Floating Point Considerations - * - * Creating a task with the @ref 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 @ref RTEMS_NO_FLOATING_POINT tasks. Saving and restoring the - * context of a @c RTEMS_FLOATING_POINT task takes longer than that of a @c - * 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 @c - * RTEMS_FLOATING_POINT task is dispatched and that task was not the last task - * to utilize the coprocessor. In a system with only one @c - * RTEMS_FLOATING_POINT task, the state of the numeric coprocessor will never - * be saved or restored. - * - * Although the overhead imposed by @c RTEMS_FLOATING_POINT tasks is minimal, - * some applications may wish to completely avoid the overhead associated with - * @c 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 @c RTEMS_NO_FLOATING_POINT task can utilize - * the numeric coprocessor without incurring the overhead of a @c - * 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 @c - * 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 @c 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 @c RTEMS_NO_FLOATING_POINT whether created as @c - * RTEMS_FLOATING_POINT or @c 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 @c RTEMS_FLOATING_POINT attribute. - * The consequence of a @c RTEMS_NO_FLOATING_POINT task attempting to access - * the floating point unit is CPU dependent but will generally result in an - * exception condition. - * - * @section ClassicTasksSecPerTaskVariables Per Task Variables - * - * Per task variables are no longer available. In particular the - * rtems_task_variable_add(), rtems_task_variable_get() and - * rtems_task_variable_delete() functions are neither declared nor defined - * anymore. Use thread local storage or POSIX Keys instead. - * - * @section ClassicTasksSecBuildingTaskAttributeSet Building a Task Attribute Set - * - * 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: - * - * - @ref RTEMS_NO_FLOATING_POINT - does not use coprocessor (default) - * - @ref RTEMS_FLOATING_POINT - uses numeric coprocessor - * - @ref RTEMS_LOCAL - local task (default) - * - @ref 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 @ref 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 @c - * RTEMS_FLOATING_POINT or @c RTEMS_LOCAL | @c RTEMS_FLOATING_POINT. The - * attribute_set parameter can be set to @c RTEMS_FLOATING_POINT because @c - * 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 - * @c RTEMS_GLOBAL | @c RTEMS_FLOATING_POINT. - * - * @section ClassicTasksSecBuildingModeAndMask Building a Mode and Mask - * - * 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: - * - * <table> - * <tr><th>Mode Constant</th><th>Mask Constant</th><th>Description</th></tr> - * <tr><td>@ref RTEMS_PREEMPT</td><td>@ref RTEMS_PREEMPT_MASK</td><td>enables preemption</td></tr> - * <tr><td>@ref RTEMS_NO_PREEMPT</td><td>@ref RTEMS_PREEMPT_MASK</td><td>disables preemption</td></tr> - * <tr><td>@ref RTEMS_NO_TIMESLICE</td><td>@ref RTEMS_TIMESLICE_MASK</td><td>disables timeslicing</td></tr> - * <tr><td>@ref RTEMS_TIMESLICE</td><td>@ref RTEMS_TIMESLICE_MASK</td><td>enables timeslicing</td></tr> - * <tr><td>@ref RTEMS_ASR</td><td>@ref RTEMS_ASR_MASK</td><td>enables ASR processing</td></tr> - * <tr><td>@ref RTEMS_NO_ASR</td><td>@ref RTEMS_ASR_MASK</td><td>disables ASR processing</td></tr> - * <tr><td>@ref RTEMS_INTERRUPT_LEVEL(0)</td><td>@ref RTEMS_INTERRUPT_MASK</td><td>enables all interrupts</td></tr> - * <tr><td>@ref RTEMS_INTERRUPT_LEVEL(n)</td><td>@ref RTEMS_INTERRUPT_MASK</td><td>sets interrupts level n</td></tr> - * </table> - * - * 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 @ref RTEMS_DEFAULT_MODES and the mask @ref - * 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 @c - * RTEMS_INTERRUPT_LEVEL(3) | @c RTEMS_NO_PREEMPT to indicate the desired - * preemption mode and interrupt level, while the mask parameter should be set - * to @c RTEMS_INTERRUPT_MASK | @c RTEMS_PREEMPT_MASK to indicate that - * the calling task's interrupt level and preemption mode are being altered. - */ - - /** - * @defgroup LocalPackages Local Packages - * - * @ingroup RTEMSAPIClassic - * - * @brief Local packages. - */ |