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@c  memmodel.t,v 1.1 2002/07/30 21:43:53 joel Exp

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@chapter Memory Model

@section Introduction

A processor may support any combination of memory

models ranging from pure physical addressing to complex demand

paged virtual memory systems.  RTEMS supports a flat memory

model which ranges contiguously over the processor's allowable

address space.  RTEMS does not support segmentation or virtual

memory of any kind.  The appropriate memory model for RTEMS

provided by the targeted processor and related characteristics

of that model are described in this chapter.

@section Flat Memory Model

Members of the ARM family newer than Version 3 support a flat

32-bit address space with addresses ranging from 0x00000000 to

0xFFFFFFFF (4 gigabytes).  Each address is represented by a

32-bit value and is byte addressable.

The address may be used to reference a

single byte, word (2-bytes), or long word (4 bytes).  Memory

accesses within this address space are performed in the endian

mode that the processor is configured for.   In general, ARM

processors are used in little endian mode.

Some of the ARM family members such as the

920 and 720 include an MMU and thus support virtual memory and

segmentation.  RTEMS does not support virtual memory or

segmentation on any of the ARM family members.