MOTOROLA
Chapter 9. Memory Management Unit (MMU)
9-13
Part II. PowerPC Microprocessor Module
The level-two base address from the level-one descriptor is indexed by EA[12Ð21] to Þnd
the level-two page descriptor. For pages larger than 1-Kbyte, the entry in the level-two table
must be duplicated according to the page size. During address translation, the msbs of the
missed effective address are replaced by the physical page address bits from the level-two
page descriptor. The number of replaced bits depends on the page size. The remaining
physical address bits are taken directly from the effective address, as shown in Table 9-2.
9.7.1 Level-One Descriptor
Table 9-3 describes the level-one descriptor format supported by the hardware to minimize
the software tablewalk routine.
Table 9-2. Number of Replaced EA Bits per Page Size
Page Size
Number of Replaced EA Bits
1 Kbyte
20
4 Kbyte
20
16 Kbyte
18
512 Kbyte
13
8 Mbyte
9
Table 9-3. Level-One Segment Descriptor Format
Bits
Name
Description
0Ð19
L2BA
Level-2 table base address. Bits 18Ð19 should be 0b00 unless MD_CTR[TWAM] = 1.
20Ð22
Ñ
Reserved
23Ð26
APG
Access protection group
27
G
Guarded memory attribute for entry
0 Nonguarded memory
1 Guarded memory
28Ð29
PS
Page size level one
00 Small (4 Kbyte or 16 Kbyte)
01 512 Kbyte
11 8 Kbyte
10 Reserved
30
WT
Writethrough attribute for entry
0 Copyback cache policy region (default)
1 Writethrough cache policy region
31
V
Level-one segment valid bit
0 Segment is not valid
1 Segment is valid
Summary of Contents for MPC860 PowerQUICC
Page 3: ...MPC860UM AD 07 98 REV 1 MPC860 PowerQUICC ª UserÕs Manual ...
Page 36: ...xxxvi MPC860 PowerQUICC UserÕs Manual MOTOROLA CONTENTS Paragraph Number Title Page Number ...
Page 78: ...I iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part I Overview ...
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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 ...
Page 262: ...9 36 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part II PowerPC Microprocessor Module ...
Page 274: ...III iv MPC860 PowerQUICC UserÕs Manual MOTOROLA Part III Configuration ...
Page 320: ...12 12 MPC860 PowerQUICC UserÕs Manual MOTOROLA Part III Configuration ...
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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