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@c COPYRIGHT (c) 1988-1999.
@c On-Line Applications Research Corporation (OAR).
@c All rights reserved.
@chapter Memory Model
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
The XXX family supports 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 big endian
fashion by the processors in this family.
Some of the XXX family members such as the
XXX, XXX, and XXX support virtual memory and
segmentation. The XXX requires external hardware support
such as the XXX Paged Memory Management Unit coprocessor
which is typically used to perform address translations for
these systems. RTEMS does not support virtual memory or
segmentation on any of the XXX family members.