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+@c
+@c  COPYRIGHT (c) 1996.
+@c  On-Line Applications Research Corporation (OAR).
+@c  All rights reserved.
+@c
+
+@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
+
+@ifinfo
+@node Overview, Overview Introduction, Preface, Top
+@end ifinfo
+@chapter Overview
+@ifinfo
+@menu
+* Overview Introduction::
+* Overview Real-time Application Systems::
+* Overview Real-time Executive::
+* Overview RTEMS Application Architecture::
+* Overview RTEMS Internal Architecture::
+* Overview User Customization and Extensibility::
+* Overview Portability::
+* Overview Memory Requirements::
+* Overview Audience::
+* Overview Conventions::
+* Overview Manual Organization::
+@end menu
+@end ifinfo
+
+@ifinfo
+@node Overview Introduction, Overview Real-time Application Systems, Overview, Overview
+@end ifinfo
+@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 C programming language.  Those
+implementation details that are processor dependent are provided
+in the C Applications Supplement documents.  A supplement
+document which addresses specific architectural issues that
+affect RTEMS is provided for each processor type that is
+supported.
+
+@ifinfo
+@node Overview Real-time Application Systems, Overview Real-time Executive, Overview Introduction, Overview
+@end ifinfo
+@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.
+
+@ifinfo
+@node Overview Real-time Executive, Overview RTEMS Application Architecture, Overview Real-time Application Systems, Overview
+@end ifinfo
+@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.
+
+@ifinfo
+@node Overview RTEMS Application Architecture, Overview RTEMS Internal Architecture, Overview Real-time Executive, Overview
+@end ifinfo
+@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.  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.
+
+@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}&
+\vrule#&
+\hbox to 0.75in{\enskip\hfil#\hfil}&
+\vrule#&
+\hbox to 0.75in{\enskip\hfil#\hfil}&
+\vrule#&
+\hbox to 0.75in{\enskip\hfil#\hfil}&
+\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.gif" WIDTH=500 HEIGHT=300 ALT="RTEMS Application Architecture">
+@end html
+@end ifset
+
+@ifinfo
+@node Overview RTEMS Internal Architecture, Overview User Customization and Extensibility, Overview RTEMS Application Architecture, Overview
+@end ifinfo
+@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:
+
+@ifset use-ascii
+@example
+@group
+           +-----------------------------------------------+
+           |          RTEMS Executive Interface            |
+           +-----------------------------------------------+
+           |                 RTEMS Core                    |
+           +-----------------------------------------------+
+           |              CPU Dependent Code               |
+           +-----------------------------------------------+
+@end group
+@end example
+@end ifset
+
+@ifset use-tex
+@c for now use the ascii version
+@example
+@group
+           +-----------------------------------------------+
+           |          RTEMS Executive Interface            |
+           +-----------------------------------------------+
+           |                 RTEMS Core                    |
+           +-----------------------------------------------+
+           |              CPU Dependent Code               |
+           +-----------------------------------------------+
+@end group
+@end example
+@tex
+@end tex
+@end ifset
+
+@ifset use-html
+@html
+<IMG SRC="rtemspie.gif" WIDTH=500 HEIGHT=300 ALT="RTEMS Architecture">
+@end html
+@end ifset
+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
+
+@ifinfo
+@node Overview User Customization and Extensibility, Overview Portability, Overview RTEMS Internal Architecture, Overview
+@end ifinfo
+@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.
+
+@ifinfo
+@node Overview Portability, Overview Memory Requirements, Overview User Customization and Extensibility, Overview
+@end ifinfo
+@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.
+
+@ifinfo
+@node Overview Memory Requirements, Overview Audience, Overview Portability, Overview
+@end ifinfo
+@section Memory Requirements
+
+Since memory is a critical resource in many real-time
+embedded systems, RTEMS was specifically designed to allow
+unused managers to be excluded from the run-time environment.
+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.  A worksheet is provided in the Memory Requirements
+chapter of the C Applications Supplement document for a specific
+target processor.  The worksheet is used to calculate the memory
+requirements of a custom RTEMS run-time environment.  The
+following managers may be optionally excluded:
+
+@itemize @bullet
+@item clock
+@item timer
+@item semaphore
+@item message
+@item event
+@item signal
+@item partition
+@item region
+@item dual ported memory
+@item I/O
+@item rate monotonic
+@item fatal error
+@item multiprocessing
+@end itemize
+
+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.
+
+@ifinfo
+@node Overview Audience, Overview Conventions, Overview Memory Requirements, Overview
+@end ifinfo
+@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 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.
+
+@ifinfo
+@node Overview Conventions, Overview Manual Organization, Overview Audience, Overview
+@end ifinfo
+@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
+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
+
+@ifinfo
+@node Overview Manual Organization, Key Concepts, Overview Conventions, Overview
+@end ifinfo
+@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:
+Initialization Manager: describes the functionality and directives
+provided by the Initialization Manager.
+
+@item Chapter 4:
+Task Manager: describes the functionality and directives provided
+by the Task Manager.
+
+@item Chapter 5:
+Interrupt Manager: describes the functionality and directives
+provided by the Interrupt Manager.
+
+@item Chapter 6:
+Clock Manager: describes the functionality and directives
+provided by the Clock Manager.
+
+@item Chapter 7
+Timer Manager: describes the functionality and directives provided
+by the Timer Manager.
+
+@item Chapter 8:
+Semaphore Manager: describes the functionality and directives
+provided by the Semaphore Manager.
+
+@item Chapter 9:
+Message Manager: describes the functionality and directives
+provided by the Message Manager.
+
+@item Chapter 10:
+Event Manager: describes the
+functionality and directives provided by the Event Manager.
+
+@item Chapter 11:
+Signal Manager: describes the
+functionality and directives provided by the Signal Manager.
+
+@item Chapter 12:
+Partition Manager: describes the
+functionality and directives provided by the Partition Manager.
+
+@item Chapter 13:
+Region Manager: describes the
+functionality and directives provided by the Region Manager.
+
+@item Chapter 14:
+Dual-Ported Memory Manager: describes
+the functionality and directives provided by the Dual-Ported
+Memory Manager.
+
+@item Chapter 15:
+I/O Manager: describes the
+functionality and directives provided by the I/O Manager.
+
+@item Chapter 16:
+Fatal Error Manager: describes the functionality and directives
+provided by the Fatal Error Manager.
+
+@item Chapter 17:
+Scheduling Concepts: details the RTEMS scheduling algorithm and
+task state transitions.
+
+@item Chapter 18:
+Rate Monotonic Manager: describes the functionality and directives
+provided by the Rate Monotonic Manager.
+
+@item Chapter 19:
+Board Support Packages: defines the
+functionality required of user-supplied board support packages.
+
+@item Chapter 20:
+User Extensions: shows the user how to
+extend RTEMS to incorporate custom features.
+
+@item Chapter 21:
+Configuring a System: details the process by which one tailors RTEMS
+for a particular single-processor or multiprocessor application.
+
+@item Chapter 22:
+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 23:
+Directive Status Codes: provides a definition of each of the
+directive status codes referenced in this manual.
+
+@item Chapter 24:
+Example Application: provides a template for simple RTEMS applications.
+
+@item Chapter 25:
+Glossary: defines terms used throughout this manual.
+
+@end table
+
+