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+The Real Time Executive for Multiprocessor Systems
+(RTEMS) is designed to be portable across multiple processor
+architectures. However, the nature of real-time systems makes
+it essential that the application designer understand certain
+processor dependent implementation details. These processor
+dependencies include calling convention, board support package
+issues, interrupt processing, exact RTEMS memory requirements,
+performance data, header files, and the assembly language
+interface to the executive.
+Each architecture represents a CPU family and usually there are
+a wide variety of CPU models within it. These models share a
+common Instruction Set Architecture (ISA) which often varies
+based upon some well-defined rules. There are often
+multiple implementations of the ISA and these may be from
+one or multiple vendors.
+On top of variations in the ISA, there may also be variations
+which occur when a CPU core implementation is combined with
+a set of peripherals to form a system on chip. For example,
+there are many ARM CPU models from numerous semiconductor
+vendors and a wide variety of peripherals. But at the
+ISA level, they share a common compatibility.
+RTEMS depends upon this core similarity across the CPU models
+and leverages that to minimize the source code that is specific
+to any particular CPU core implementation or CPU model.
+This manual is separate and distinct from the RTEMS Porting
+Guide. That manual is a guide on porting RTEMS to a new
+architecture. This manual is focused on the more mundane
+CPU architecture specific issues that may impact
+application development. For example, if you need to write
+a subroutine in assembly language, it is critical to understand
+the calling conventions for the target architecture.
+The first chapter in this manual describes these issues
+in general terms. In a sense, it is posing the questions
+one should be aware may need to be answered and understood
+when porting an RTEMS application to a new architecture.
+Each subsequent chapter gives the answers to those questions
+for a particular CPU architecture.
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+.. COMMENT: All rights reserved.