source: rtems-docs/cpu-supplement/preface.rst @ 72a62ad

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