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+@c
+@c  COPYRIGHT (c) 1996.
+@c  On-Line Applications Research Corporation (OAR).
+@c  All rights reserved.
+@c
+
+@ifinfo
+@node Preface, Overview, Top, Top
+@end ifinfo
+@unnumbered Preface
+
+In recent years, the cost required to develop a
+software product has increased significantly while the target
+hardware costs have decreased.  Now a larger portion of money is
+expended in developing, using, and maintaining software.  The
+trend in computing costs is the complete dominance of software
+over hardware costs.  Because of this, it is necessary that
+formal disciplines be established to increase the probability
+that software is characterized by a high degree of correctness,
+maintainability, and portability.  In addition, these
+disciplines must promote practices that aid in the consistent
+and orderly development of a software system within schedule and
+budgetary constraints.  To be effective, these disciplines must
+adopt standards which channel individual software efforts toward
+a common goal.
+
+The push for standards in the software development
+field has been met with various degrees of success.  The
+Microprocessor Operating Systems Interfaces (MOSI) effort has
+experienced only limited success.  As popular as the UNIX
+operating system has grown, the attempt to develop a standard
+interface definition to allow portable application development
+has only recently begun to produce the results needed in this
+area.  Unfortunately, very little effort has been expended to
+provide standards addressing the needs of the real-time
+community.  Several organizations have addressed this need
+during recent years.
+
+The Real Time Executive Interface Definition (RTEID)
+was developed by Motorola with technical input from Software
+Components Group.  RTEID was adopted by the VMEbus International
+Trade Association (VITA) as a baseline draft for their proposed
+standard multiprocessor, real-time executive interface, Open
+Real-Time Kernel Interface Definition (ORKID).  These two groups
+are currently working together with the IEEE P1003.4 committee
+to insure that the functionality of their proposed standards is
+adopted as the real-time extensions to POSIX.
+
+This emerging standard defines an interface for the
+development of real-time software to ease the writing of
+real-time application programs that are directly portable across
+multiple real-time executive implementations.  This interface
+includes both the source code interfaces and run-time behavior
+as seen by a real-time application.  It does not include the
+details of how a kernel implements these functions.  The
+standard's goal is to serve as a complete definition of external
+interfaces so that application code that conforms to these
+interfaces will execute properly in all real-time executive
+environments.  With the use of a standards compliant executive,
+routines that acquire memory blocks, create and manage message
+queues, establish and use semaphores, and send and receive
+signals need not be redeveloped for a different real-time
+environment as long as the new environment is compliant with the
+standard.  Software developers need only concentrate on the
+hardware dependencies of the real-time system.  Furthermore,
+most hardware dependencies for real-time applications can be
+localized to the device drivers.
+
+A compliant executive provides simple and flexible
+real-time multiprocessing.  It easily lends itself to both
+tightly-coupled and loosely-coupled configurations (depending on
+the system hardware configuration).  Objects such as tasks,
+queues, events, signals, semaphores, and memory blocks can be
+designated as global objects and accessed by any task regardless
+of which processor the object and the accessing task reside.
+
+The acceptance of a standard for real-time executives
+will produce the same advantages enjoyed from the push for UNIX
+standardization by AT&T's System V Interface Definition and
+IEEE's POSIX efforts.  A compliant multiprocessing executive
+will allow close coupling between UNIX systems and real-time
+executives to provide the many benefits of the UNIX development
+environment to be applied to real-time software development.
+Together they provide the necessary laboratory environment to
+implement real-time, distributed, embedded systems using a wide
+variety of computer architectures.
+
+A study was completed in 1988, within the Research,
+Development, and Engineering Center, U.S. Army Missile Command,
+which compared the various aspects of the Ada programming
+language as they related to the application of Ada code in
+distributed and/or multiple processing systems.  Several
+critical conclusions were derived from the study.  These
+conclusions have a major impact on the way the Army develops
+application software for embedded applications. These impacts
+apply to both in-house software development and contractor
+developed software.
+
+A conclusion of the analysis, which has been
+previously recognized by other agencies attempting to utilize
+Ada in a distributed or multiprocessing environment, is that the
+Ada programming language does not adequately support
+multiprocessing.  Ada does provide a mechanism for
+multi-tasking, however, this capability exists only for a single
+processor system.  The language also does not have inherent
+capabilities to access global named variables, flags or program
+code.  These critical features are essential in order for data
+to be shared between processors.  However, these drawbacks do
+have workarounds which are sometimes awkward and defeat the
+intent of software maintainability and portability goals.
+
+Another conclusion drawn from the analysis, was that
+the run time executives being delivered with the Ada compilers
+were too slow and inefficient to be used in modern missile
+systems.  A run time executive is the core part of the run time
+system code, or operating system code, that controls task
+scheduling, input/output management and memory management.
+Traditionally, whenever efficient executive (also known as
+kernel) code was required by the application, the user developed
+in-house software.  This software was usually written in
+assembly language for optimization.
+
+Because of this shortcoming in the Ada programming
+language, software developers in research and development and
+contractors for project managed systems, are mandated by
+technology to purchase and utilize off-the-shelf third party
+kernel code.  The contractor, and eventually the Government,
+must pay a licensing fee for every copy of the kernel code used
+in an embedded system.
+
+The main drawback to this development environment is
+that the Government does not own, nor has the right to modify
+code contained within the kernel.  V&V techniques in this
+situation are more difficult than if the complete source code
+were available. Responsibility for system failures due to faulty
+software is yet another area to be resolved under this
+environment.
+
+The Guidance and Control Directorate began a software
+development effort to address these problems.  A project to
+develop an experimental run time kernel was begun that will
+eliminate the major drawbacks of the Ada programming language
+mentioned above. The Real Time Executive for Multiprocessor Systems
+(RTEMS) provides full capabilities for management of tasks,
+interrupts, time, and multiple processors in addition to those
+features typical of generic operating systems.  The code is
+Government owned, so no licensing fees are necessary.  RTEMS has
+been implemented in both the Ada and C programming languages.
+It has been ported to the Motorola MC68xxx family, the Intel
+i80386 and above, and the Intel i80960 family.  Support for
+other processor families, including RISC, CISC, and DSP, is
+planned.  Since almost all of RTEMS is written in a high level
+language, ports to additional processor families require minimal
+effort.
+
+RTEMS multiprocessor support is capable of handling
+either homogeneous or heterogeneous systems.  The kernel
+automatically compensates for architectural differences (byte
+swapping, etc.) between processors.  This allows a much easier
+transition from one processor family to another without a major
+system redesign.
+
+Since the proposed standards are still in draft form,
+RTEMS cannot and does not claim compliance.  However, the status
+of the standard is being carefully monitored to guarantee that
+RTEMS provides the functionality specified in the standard.
+Once approved, RTEMS will be made compliant.
+
+This document is a detailed users guide for a
+functionally compliant real-time multiprocessor executive.  It
+describes the user interface and run-time behavior of Release
+@value{RTEMS-RELEASE} of the C implementation of RTEMS.
+