source: rtems/doc/supplements/i386/cpumodel.texi @ 3e6d749

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@c  COPYRIGHT (c) 1988-1998.
@c  On-Line Applications Research Corporation (OAR).
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@ifinfo
@node CPU Model Dependent Features, CPU Model Dependent Features Introduction, Preface, Top
@end ifinfo
@chapter CPU Model Dependent Features
@ifinfo
@menu
* CPU Model Dependent Features Introduction::
* CPU Model Dependent Features CPU Model Name::
* CPU Model Dependent Features bswap Instruction::
* CPU Model Dependent Features Floating Point Unit::
@end menu
@end ifinfo

@ifinfo
@node CPU Model Dependent Features Introduction, CPU Model Dependent Features CPU Model Name, CPU Model Dependent Features, CPU Model Dependent Features
@end ifinfo
@section Introduction

Microprocessors are generally classified into
families with a variety of CPU models or implementations within
that family.  Within a processor family, there is a high level
of binary compatibility.  This family may be based on either an
architectural specification or on maintaining compatibility with
a popular processor.  Recent microprocessor families such as the
SPARC or PA-RISC are based on an architectural specification
which is independent or any particular CPU model or
implementation.  Older families such as the M68xxx and the iX86
evolved as the manufacturer strived to produce higher
performance processor models which maintained binary
compatibility with older models.

RTEMS takes advantage of the similarity of the
various models within a CPU family.  Although the models do vary
in significant ways, the high level of compatibility makes it
possible to share the bulk of the CPU dependent executive code
across the entire family.  Each processor family supported by
RTEMS has a list of features which vary between CPU models
within a family.  For example, the most common model dependent
feature regardless of CPU family is the presence or absence of a
floating point unit or coprocessor.  When defining the list of
features present on a particular CPU model, one simply notes
that floating point hardware is or is not present and defines a
single constant appropriately.  Conditional compilation is
utilized to include the appropriate source code for this CPU
model's feature set.  It is important to note that this means
that RTEMS is thus compiled using the appropriate feature set
and compilation flags optimal for this CPU model used.  The
alternative would be to generate a binary which would execute on
all family members using only the features which were always
present.

This chapter presents the set of features which vary
across i386 implementations and are of importance to RTEMS.
The set of CPU model feature macros are defined in the file
c/src/exec/score/cpu/i386/i386.h based upon the particular CPU
model defined on the compilation command line.

@ifinfo
@node CPU Model Dependent Features CPU Model Name, CPU Model Dependent Features bswap Instruction, CPU Model Dependent Features Introduction, CPU Model Dependent Features
@end ifinfo
@section CPU Model Name

The macro CPU_MODEL_NAME is a string which designates
the name of this CPU model.  For example, for the Intel i386 without an
i387 coprocessor, this macro is set to the string "i386 with i387".

@ifinfo
@node CPU Model Dependent Features bswap Instruction, CPU Model Dependent Features Floating Point Unit, CPU Model Dependent Features CPU Model Name, CPU Model Dependent Features
@end ifinfo
@section bswap Instruction

The macro I386_HAS_BSWAP is set to 1 to indicate that
this CPU model has the @code{bswap} instruction which
endian swaps a thirty-two bit quantity.  This instruction
appears to be present in all CPU models
i486's and above.


@ifinfo
@node CPU Model Dependent Features Floating Point Unit, Calling Conventions, CPU Model Dependent Features bswap Instruction , CPU Model Dependent Features
@end ifinfo
@section Floating Point Unit

The macro I386_HAS_FPU is set to 1 to indicate that
this CPU model has a hardware floating point unit and 0
otherwise.  The hardware floating point may be on-chip (as in the
case of an i486DX or Pentium) or as a coprocessor (as in the case of
an i386/i387 combination).