MOTOROLA
Chapter 9. Memory Management Unit (MMU)
9-7
Part II. PowerPC Microprocessor Module
9.5 Protection Resolution Modes
The MMUs can be programmed in three different modes that different methods of deÞning
the protection resolution of the address space. These are as follows:
¥
Mode 1ÑProtection resolution to 4-Kbyte minimum page size. This is the simplest
mode with the most efÞcient memory size (that is, MMU tables are smaller). Use
this mode if 1-Kbyte protection resolution is not required.
In this mode, set the following:
Ñ MD_CTR[TWAM] = 1
Ñ Mx_CTR[PPM] = 0
Ñ Bits 20Ð27 of the level-two descriptor take on the meaning described in the right
¥
Mode 2ÑProtection resolution to 1-Kbyte minimum subpage size, where all
4-Kbyte subpages map to the same physical page but may have different protection
attributes.
In this mode, set the following:
Ñ MD_CTR[TWAM]=1
Ñ Mx_CTR[PPM]=1
For pages larger than 4 Kbytes, bits 20Ð27 of the level-two descriptor take on the
meaning described in the right side of Table 9-4
For 4-Kbyte pages, set the subpage validity ßags (bits 20Ð27) to subpage protection
mode for 4 subpages; see Table 9-4. In this mode, the MMU page tables deÞned for
the software tablewalk resolve to a single level-two descriptor entry for a 4-Kbyte
page.
Page protection (and thus level-two descriptor entries) for pages larger than 4-Kbyte
is the same as for mode 1, described above. However, for 4-Kbyte pages, the
level-two descriptor encoding has special meaning. The level-two descriptor deÞnes
a 4-Kbyte page in physical memory, but each 1-Kbyte of that page can be deÞned
with different protection attributes.
This mode is just as efÞcient in memory size as mode 1, but the protection encoding
and capabilities for 4-Kbyte pages differ.
¥
Mode 3ÑProtection resolution to 1-Kbyte minimum subpage size, with no
restriction on subpage mapping. In this mode, set:
Ñ MD_CTR[TWAM] = 0
Ñ Mx_CTR[PPM] = 0
Ñ Mx_CTR[PPC5] = 0
Summary of Contents for MPC860 PowerQUICC
Page 3: ...MPC860UM AD 07 98 REV 1 MPC860 PowerQUICC ª UserÕs Manual ...
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Page 78: ...I iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
Page 88: ...1 10 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
Page 114: ...3 16 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
Page 226: ...8 32 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part II PowerPC Microprocessor Module ...
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Page 274: ...III iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part III Configuration ...
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Page 325: ...MOTOROLA Part IV Hardware Interface IV v Part IV Hardware Interface ...
Page 326: ...IV vi MPC860 PowerQUICC UserÕs Manual MOTOROLA Part IV Hardware Interface ...
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Page 632: ...21 44 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
Page 660: ...22 28 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part V The Communications Processor Module ...
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Page 998: ...37 48 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part VI Debug and Test ...
Page 1016: ...A 10 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
Page 1024: ...B 8 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
Page 1030: ...C 6 MPC860 PowerQUICC UserÕs Manual MOTOROLA Appendixes ...
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