9-14
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part II. PowerPC Microprocessor Module
9.7.2 Level-Two Descriptor
Table 9-4 describes the level-two descriptor format supported by hardware.
9.8 Programming Model
All MMU programming model registers are supervisor-level SPRs that are accessed by
using mtspr and mfspr. Attempting to access these SPRs in user mode causes a program
exception. The PowerPC tlbie and tlbia instructions can be used to invalidate TLBs. MMU
registers should be accessed when both MSR[IR]
= 0 and MSR[DR]
= 0. No similar
restriction exists for tlbie and tlbia.
Table 9-4. Level-Two (Page) Descriptor Format
Bits
Name
4-Kbyte Pages AND
Mx_CTR[PPM] = 1
Larger than 4-Kbyte Pages OR
Mx_CTR[PPM] = 0
0Ð19
RPN
Physical (real) page number
20Ð21 PP
Protection
for 1st
1-Kbyte
subpage in
a 4-Kbyte
page
For Instruction Pages
Supervisor User
00 No access No access
01 Executable No access
1x Executable Executable
For Data Pages
Supervisor User
00 No access No access
01 R/W
No access
10 R/W
R/O
11 R/W
R/W
For Instruction Pages
Supervisor User
Extended encoding:
00 No access No access
01 Executable No access
1x Reserved
PowerPC encoding:
00 Executable No access
01 Executable Executable
1x Executable Executable
For Data Pages
Supervisor User
Extended encoding:
00 No access No access
01 R/O
No access
1x Reserved
PowerPC encoding:
00 R/W
No access
01 R/W
R/O
10 R/W
R/W
11 R/O
R/O
22
PP
2nd
1-Kbyte
subpage
0 Bits 20Ð21 contain PowerPC encoding
1 Bits 20Ð21 contain extended encoding
23
CÑChange bit for entry. Set to 1 by default if change
tracking functionality is not desired.
0 Unchanged region (write-protected)
1 Changed region, write allowed
24Ð25
3rd 1-Kbyte
subpage
MD_CTR[PPCS] = 0.
For 1 Kbyte pages in
mode 3, set to the
appropriate subpage
validity (see Section 9.5,
ÒProtection Resolution
ModesÓ). Otherwise, set to
0b1111.
MD_CTR[PPCS] = 1
1000 Hit (supervisor accesses
only)
0100 Hit (user accesses only)
1100 Hit for both
26Ð27
4th 1-Kbyte
subpage
28
SPS
Clear
Small page size. Valid only when L1 descriptor[PS] = 00
0 4 Kbyte
1 16 Kbyte
29
SH
Shared page
0 Entry matches only if a TLB entryÕs ASID Þeld matches the value in M_CASID.
1 ASID comparison is disabled for the entry.
30
CI
Cache-inhibit attribute for the entry.
31
V
Page valid bit
Содержание MPC860 PowerQUICC
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Страница 325: ...MOTOROLA Part IV Hardware Interface IV v Part IV Hardware Interface ...
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