source: rtems/doc/supplements/mips64orion/cpumodel.t @ f48b1000

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1@c
2@c  COPYRIGHT (c) 1988-1998.
3@c  On-Line Applications Research Corporation (OAR).
4@c  All rights reserved.
5@c
6@c  $Id$
7@c
8
9@chapter CPU Model Dependent Features
10
11@section Introduction
12
13Microprocessors are generally classified into
14families with a variety of CPU models or implementations within
15that family.  Within a processor family, there is a high level
16of binary compatibility.  This family may be based on either an
17architectural specification or on maintaining compatibility with
18a popular processor.  Recent microprocessor families such as the
19SPARC or PA-RISC are based on an architectural specification
20which is independent or any particular CPU model or
21implementation.  Older families such as the M68xxx and the iX86
22evolved as the manufacturer strived to produce higher
23performance processor models which maintained binary
24compatibility with older models.
25
26RTEMS takes advantage of the similarity of the
27various models within a CPU family.  Although the models do vary
28in significant ways, the high level of compatibility makes it
29possible to share the bulk of the CPU dependent executive code
30across the entire family.  Each processor family supported by
31RTEMS has a list of features which vary between CPU models
32within a family.  For example, the most common model dependent
33feature regardless of CPU family is the presence or absence of a
34floating point unit or coprocessor.  When defining the list of
35features present on a particular CPU model, one simply notes
36that floating point hardware is or is not present and defines a
37single constant appropriately.  Conditional compilation is
38utilized to include the appropriate source code for this CPU
39model's feature set.  It is important to note that this means
40that RTEMS is thus compiled using the appropriate feature set
41and compilation flags optimal for this CPU model used.  The
42alternative would be to generate a binary which would execute on
43all family members using only the features which were always
44present.
45
46This chapter presents the set of features which vary
47across SPARC implementations and are of importance to RTEMS.
48The set of CPU model feature macros are defined in the file
49c/src/exec/score/cpu/XXX/XXX.h based upon the particular CPU
50model defined on the compilation command line.
51
52@section CPU Model Name
53
54The macro CPU_MODEL_NAME is a string which designates
55the name of this CPU model.  For example, for the MODEL
56processor, this macro is set to the string "XXX".
57
58@section Floating Point Unit
59
60The macro XXX_HAS_FPU is set to 1 to indicate that
61this CPU model has a hardware floating point unit and 0
62otherwise.  It does not matter whether the hardware floating
63point support is incorporated on-chip or is an external
64coprocessor.
65
66@section Another Optional Feature
67
68The macro XXX
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