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44 lines
2.2 KiB
ReStructuredText
.. SPDX-License-Identifier: CC-BY-SA-4.0
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.. Copyright (C) 1988, 2002 On-Line Applications Research Corporation (OAR)
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Preface
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*******
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The Real Time Executive for Multiprocessor Systems (RTEMS) is designed to be
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portable across multiple processor architectures. However, the nature of
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real-time systems makes it essential that the application designer understand
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certain processor dependent implementation details. These processor
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dependencies include calling convention, board support package issues,
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interrupt processing, exact RTEMS memory requirements, performance data, header
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files, and the assembly language interface to the executive.
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Each architecture represents a CPU family and usually there are a wide variety
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of CPU models within it. These models share a common Instruction Set
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Architecture (ISA) which often varies based upon some well-defined rules.
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There are often multiple implementations of the ISA and these may be from one
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or multiple vendors.
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On top of variations in the ISA, there may also be variations which occur when
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a CPU core implementation is combined with a set of peripherals to form a
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system on chip. For example, there are many ARM CPU models from numerous
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semiconductor vendors and a wide variety of peripherals. But at the ISA level,
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they share a common compatibility.
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RTEMS depends upon this core similarity across the CPU models and leverages
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that to minimize the source code that is specific to any particular CPU core
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implementation or CPU model.
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This manual is separate and distinct from the RTEMS Porting Guide. That manual
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is a guide on porting RTEMS to a new architecture. This manual is focused on
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the more mundane CPU architecture specific issues that may impact application
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development. For example, if you need to write a subroutine in assembly
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language, it is critical to understand the calling conventions for the target
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architecture.
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The first chapter in this manual describes these issues in general terms. In a
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sense, it is posing the questions one should be aware may need to be answered
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and understood when porting an RTEMS application to a new architecture. Each
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subsequent chapter gives the answers to those questions for a particular CPU
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architecture.
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