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@c  On-Line Applications Research Corporation (OAR).

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@c  cpumodel.t,v 1.6 2002/01/17 21:47:46 joel Exp

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@chapter CPU Model Dependent Features

@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 PA-RISC implementations and are of importance to RTEMS.

The set of CPU model feature macros are defined in the file

c/src/exec/score/cpu/hppa1_1/hppa.h based upon the particular CPU

model defined on the compilation command line.

@section CPU Model Name

The macro CPU_MODEL_NAME is a string which designates

the name of this CPU model.  For example, for the Hewlett Packard

PA-7100 CPU model, this macro is set to the string "hppa 7100".