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authorJoel Sherrill <joel@rtems.org>2016-11-15 10:37:59 -0600
committerJoel Sherrill <joel@rtems.org>2017-01-11 12:13:21 -0600
commit48a7fa31f918a6fc88719b3c9393a9ba2829f42a (patch)
tree10bf638de133099fcabe5fe713ca98a546a27ab2 /doc/user/overview.t
parent7a4b264574ce81d5473de6d15950464ea2cff485 (diff)
downloadrtems-48a7fa31f918a6fc88719b3c9393a9ba2829f42a.tar.bz2
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closes #2812.
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-@c
-@c COPYRIGHT (c) 1988-2008.
-@c On-Line Applications Research Corporation (OAR).
-@c All rights reserved.
-
-@c
-@c This chapter is missing the following figures:
-@c
-@c Figure 1-1 RTEMS Application Architecture
-@c Figure 1-2 RTEMS Internal Architecture
-@c
-
-@chapter Overview
-
-@section 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:
-
-@itemize @bullet
-@item multitasking capabilities
-@item homogeneous and heterogeneous multiprocessor systems
-@item event-driven, priority-based, preemptive scheduling
-@item optional rate monotonic scheduling
-@item intertask communication and synchronization
-@item priority inheritance
-@item responsive interrupt management
-@item dynamic memory allocation
-@item high level of user configurability
-@end itemize
-
-This manual describes the usage of RTEMS for
-applications written in the @value{LANGUAGE} 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 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 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 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.
-
-@float Figure,fig:RTEMS-App-Arch
-@caption{RTEMS Application Architecture}
-
-@ifset use-ascii
-@example
-@group
- +-----------------------------------------------------------+
- | Application Dependent Software |
- | +----------------------------------------+ |
- | | Standard Application Components | |
- | | +-------------+---+ |
- | +---+-----------+ | | |
- | | Board Support | | RTEMS | |
- | | Package | | | |
- +----+---------------+--------------+-----------------+-----|
- | Target Hardware |
- +-----------------------------------------------------------+
-@end group
-@end example
-@end ifset
-
-@ifset use-tex
-@sp 1
-@tex
-\centerline{\vbox{\offinterlineskip\halign{
-\vrule#&
-\hbox to 0.50in{\enskip\hfil#\hfil}&
-\vrule#&
-\hbox to 0.50in{\enskip\hfil#\hfil}&
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-\vrule#&
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-\vrule#&
-\hbox to 0.75in{\enskip\hfil#\hfil}&
-\vrule#&
-\hbox to 0.50in{\enskip\hfil#\hfil}&
-\vrule#&
-\hbox to 0.50in{\enskip\hfil#\hfil}&
-\vrule#\cr
-\multispan{17}\hrulefill\cr
-% to force all columns to desired width
-& \enskip && \enskip && \enskip && \enskip &&
- \enskip && \enskip &&\enskip &&\enskip &\cr
-% For debugging columns
-%& \enskip 0&& \enskip 1&& \enskip 2&& \enskip 3&&
-% \enskip 4&& \enskip 5&&\enskip 6&&\enskip 7&\cr
-\strut&\multispan{15}&\cr
-&\multispan{15}\hfil Application Dependent Software\hfil&\cr
-\strut&\multispan{15}&\cr
-&\multispan{2}&&\multispan{8}\hrulefill &\multispan{2}&\cr
-\strut&\multispan{2}&&&\multispan{7}&&\multispan{2}&&\cr
-&\multispan{2}&&&\multispan{7}\hfil Standard Application Components\hfil&
- &\multispan{2}&&\cr
-\strut&\multispan{2}&&&\multispan{7}&&\multispan{2}&&\cr
-&&\multispan{5}\hrulefill&&\multispan{7}\hrulefill&&\cr
-\strut&&&\multispan{3} &&&&\multispan{5}&&&\cr
-&&&\multispan{3}\hfil Device\hfil&&&&\multispan{5}\hfil RTEMS\hfil&&&\cr
-&&&\multispan{3}\hfil Drivers\hfil&&&&\multispan{5}&&&\cr
-\strut&&&\multispan{3} &&&&\multispan{5}&&&\cr
-\multispan{17}\hrulefill\cr
-\strut&\multispan{15}&\cr
-&\multispan{15}\hfil Target Hardware\hfil&\cr
-\strut&\multispan{15}&\cr
-\multispan{17}\hrulefill\cr
-}}\hfil}
-@end tex
-@end ifset
-
-@ifset use-html
-@html
-<IMG SRC="rtemsarc.png" WIDTH=500 HEIGHT=300 ALT="RTEMS Application Architecture">
-@end html
-@end ifset
-@end float
-
-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 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:
-
-@float Figure,fig:rtems-layers
-@caption{RTEMS Layered Architecture}
-
-@ifset use-ascii
-@example
-@group
- +-----------------------------------------------+
- | RTEMS Executive Interface |
- +-----------------------------------------------+
- | RTEMS Core |
- +-----------------------------------------------+
- | CPU Dependent Code |
- +-----------------------------------------------+
-@end group
-@end example
-@end ifset
-
-@ifset use-tex
-@center{@image{rtemspie,4in,3in, RTEMS Layered Architecture}}
-@tex
-@end tex
-@end ifset
-
-@ifset use-html
-@html
-<IMG SRC="rtemspie.png" WIDTH=500 HEIGHT=300 ALT="RTEMS Layered Architecture">
-@end html
-@end ifset
-@end float
-
-Subsequent chapters present a detailed description of the capabilities
-provided by each of the following RTEMS managers:
-
-@itemize @bullet
-@item initialization
-@item task
-@item interrupt
-@item clock
-@item timer
-@item semaphore
-@item message
-@item event
-@item signal
-@item partition
-@item region
-@item dual ported memory
-@item I/O
-@item fatal error
-@item rate monotonic
-@item user extensions
-@item multiprocessing
-@end itemize
-
-@section 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.
-
-@section 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 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
-@ref{Configuring a System} for more details.
-
-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 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 @value{LANGUAGE}, a basic
-understanding of the @value{LANGUAGE} 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.
-
-@section Conventions
-
-The following conventions are used in this manual:
-
-@itemize @bullet
-@item Significant words or phrases as well as all directive
-names are printed in bold type.
-
-@item 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
-@value{STRUCTURE} definitions which can be incorporated into the user
-application.
-
-@item A number of type definitions are provided by RTEMS and
-can be found in rtems.h.
-
-@item The characters "0x" preceding a number indicates that
-the number is in hexadecimal format. Any other numbers are
-assumed to be in decimal format.
-@end itemize
-
-@section 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:
-
-@itemize @bullet
-@item Calling sequence
-@item Directive status codes
-@item Description
-@item Notes
-@end itemize
-
-The following provides an overview of the remainder
-of this manual:
-
-@table @asis
-@item Chapter 2:
-Key Concepts: presents an introduction to the ideas which are common
-across multiple RTEMS managers.
-
-@item Chapter 3:
-RTEMS Data Types: describes the fundamental data types shared
-by the services in the RTEMS Classic API.
-
-@item Chapter 4:
-Scheduling Concepts: details the various RTEMS scheduling algorithms
-and task state transitions.
-
-@item Chapter 5:
-Initialization Manager: describes the functionality and directives
-provided by the Initialization Manager.
-
-@item Chapter 6:
-Task Manager: describes the functionality and directives provided
-by the Task Manager.
-
-@item Chapter 7:
-Interrupt Manager: describes the functionality and directives
-provided by the Interrupt Manager.
-
-@item Chapter 8:
-Clock Manager: describes the functionality and directives
-provided by the Clock Manager.
-
-@item Chapter 9:
-Timer Manager: describes the functionality and directives provided
-by the Timer Manager.
-
-@item Chapter 10:
-Rate Monotonic Manager: describes the functionality and directives
-provided by the Rate Monotonic Manager.
-
-@item Chapter 11:
-Semaphore Manager: describes the functionality and directives
-provided by the Semaphore Manager.
-
-@item Chapter 12:
-Barrier Manager: describes the functionality and directives
-provided by the Barrier Manager.
-
-@item Chapter 13:
-Message Manager: describes the functionality and directives
-provided by the Message Manager.
-
-@item Chapter 14:
-Event Manager: describes the
-functionality and directives provided by the Event Manager.
-
-@item Chapter 15:
-Signal Manager: describes the
-functionality and directives provided by the Signal Manager.
-
-@item Chapter 16:
-Partition Manager: describes the
-functionality and directives provided by the Partition Manager.
-
-@item Chapter 17:
-Region Manager: describes the
-functionality and directives provided by the Region Manager.
-
-@item Chapter 18:
-Dual-Ported Memory Manager: describes
-the functionality and directives provided by the Dual-Ported
-Memory Manager.
-
-@item Chapter 19:
-I/O Manager: describes the
-functionality and directives provided by the I/O Manager.
-
-@item Chapter 20:
-Fatal Error Manager: describes the functionality and directives
-provided by the Fatal Error Manager.
-
-@item Chapter 21:
-Board Support Packages: defines the
-functionality required of user-supplied board support packages.
-
-@item Chapter 22:
-User Extensions: shows the user how to
-extend RTEMS to incorporate custom features.
-
-@item Chapter 23:
-Configuring a System: details the process by which one tailors RTEMS
-for a particular single-processor or multiprocessor application.
-
-@item 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.
-
-@item 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.
-
-@item 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.
-
-@item 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.
-
-@item 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.
-
-@item Chapter 29:
-Timespec Helpers: presents a set of helper services useful
-when manipulating POSIX @code{struct timespec} instances.
-
-@item Chapter 30:
-Constant Bandwidth Server Scheduler API::
-
-@item Chapter 31:
-Directive Status Codes: provides a definition of each of the
-directive status codes referenced in this manual.
-
-@item Chapter 32:
-Example Application: provides a template for simple RTEMS applications.
-
-@item Chapter 33:
-Glossary: defines terms used throughout this manual.
-
-@end table
-
-