@c @c COPYRIGHT (c) 1988-2002. @c On-Line Applications Research Corporation (OAR). @c All rights reserved. @c @c $Id$ @c @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 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.