1 | .. comment SPDX-License-Identifier: CC-BY-SA-4.0 |
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2 | |
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3 | .. COMMENT: COPYRIGHT (c) 1988-2002. |
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4 | .. COMMENT: On-Line Applications Research Corporation (OAR). |
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5 | .. COMMENT: All rights reserved. |
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6 | |
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7 | ======= |
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8 | Preface |
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9 | ======= |
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10 | |
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11 | The Real Time Executive for Multiprocessor Systems (RTEMS) is designed to be |
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12 | portable across multiple processor architectures. However, the nature of |
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13 | real-time systems makes it essential that the application designer understand |
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14 | certain processor dependent implementation details. These processor |
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15 | dependencies include calling convention, board support package issues, |
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16 | interrupt processing, exact RTEMS memory requirements, performance data, header |
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17 | files, and the assembly language interface to the executive. |
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18 | |
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19 | Each architecture represents a CPU family and usually there are a wide variety |
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20 | of CPU models within it. These models share a common Instruction Set |
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21 | Architecture (ISA) which often varies based upon some well-defined rules. |
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22 | There are often multiple implementations of the ISA and these may be from one |
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23 | or multiple vendors. |
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24 | |
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25 | On top of variations in the ISA, there may also be variations which occur when |
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26 | a CPU core implementation is combined with a set of peripherals to form a |
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27 | system on chip. For example, there are many ARM CPU models from numerous |
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28 | semiconductor vendors and a wide variety of peripherals. But at the ISA level, |
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29 | they share a common compatibility. |
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30 | |
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31 | RTEMS depends upon this core similarity across the CPU models and leverages |
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32 | that to minimize the source code that is specific to any particular CPU core |
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33 | implementation or CPU model. |
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34 | |
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35 | This manual is separate and distinct from the RTEMS Porting Guide. That manual |
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36 | is a guide on porting RTEMS to a new architecture. This manual is focused on |
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37 | the more mundane CPU architecture specific issues that may impact application |
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38 | development. For example, if you need to write a subroutine in assembly |
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39 | language, it is critical to understand the calling conventions for the target |
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40 | architecture. |
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41 | |
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42 | The first chapter in this manual describes these issues in general terms. In a |
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43 | sense, it is posing the questions one should be aware may need to be answered |
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44 | and understood when porting an RTEMS application to a new architecture. Each |
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45 | subsequent chapter gives the answers to those questions for a particular CPU |
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46 | architecture. |
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