1 | @c |
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2 | @c COPYRIGHT (c) 1988-1996. |
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3 | @c On-Line Applications Research Corporation (OAR). |
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4 | @c All rights reserved. |
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5 | @c |
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6 | @c $Id$ |
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7 | @c |
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8 | |
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9 | @ifinfo |
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10 | @node Memory Model, Memory Model Introduction, Calling Conventions User-Provided Routines, Top |
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11 | @end ifinfo |
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12 | @chapter Memory Model |
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13 | @ifinfo |
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14 | @menu |
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15 | * Memory Model Introduction:: |
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16 | * Memory Model Flat Memory Model:: |
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17 | @end menu |
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18 | @end ifinfo |
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19 | |
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20 | @ifinfo |
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21 | @node Memory Model Introduction, Memory Model Flat Memory Model, Memory Model, Memory Model |
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22 | @end ifinfo |
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23 | @section Introduction |
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24 | |
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25 | A processor may support any combination of memory |
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26 | models ranging from pure physical addressing to complex demand |
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27 | paged virtual memory systems. RTEMS supports a flat memory |
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28 | model which ranges contiguously over the processor's allowable |
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29 | address space. RTEMS does not support segmentation or virtual |
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30 | memory of any kind. The appropriate memory model for RTEMS |
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31 | provided by the targeted processor and related characteristics |
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32 | of that model are described in this chapter. |
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33 | |
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34 | @ifinfo |
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35 | @node Memory Model Flat Memory Model, Interrupt Processing, Memory Model Introduction, Memory Model |
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36 | @end ifinfo |
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37 | @section Flat Memory Model |
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38 | |
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39 | The MC68xxx family supports a flat 32-bit address |
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40 | space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4 |
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41 | gigabytes). Each address is represented by a 32-bit value and |
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42 | is byte addressable. The address may be used to reference a |
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43 | single byte, word (2-bytes), or long word (4 bytes). Memory |
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44 | accesses within this address space are performed in big endian |
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45 | fashion by the processors in this family. |
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46 | |
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47 | Some of the MC68xxx family members such as the |
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48 | MC68020, MC68030, and MC68040 support virtual memory and |
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49 | segmentation. The MC68020 requires external hardware support |
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50 | such as the MC68851 Paged Memory Management Unit coprocessor |
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51 | which is typically used to perform address translations for |
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52 | these systems. RTEMS does not support virtual memory or |
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53 | segmentation on any of the MC68xxx family members. |
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54 | |
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