Motorola MPC860 PowerQUICC User Manual page 240

Part II. PowerPC Microprocessor Module
9.7.2 Level-Two Descriptor
Table 9-4 describes the level-two descriptor format supported by hardware.
Table 9-4. Level-Two (Page) Descriptor Format
4-Kbyte Pages AND
Bits Name
Mx_CTR[PPM] = 1
0Ð19 RPN Physical (real) page number
20Ð21 PP Protection
for 1st
1-Kbyte
subpage in
a 4-Kbyte
page
22 PP 2nd
1-Kbyte
subpage
23
24Ð25 3rd 1-Kbyte
subpage
26Ð27 4th 1-Kbyte
subpage
28 SPS Clear
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
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.
9-14
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
MPC860 PowerQUICC UserÕs Manual
Larger than 4-Kbyte Pages OR
Mx_CTR[PPM] = 0
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
0 Bits 20Ð21 contain PowerPC encoding
1 Bits 20Ð21 contain extended encoding
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
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.
Small page size. Valid only when L1 descriptor[PS] = 00
0 4 Kbyte
1 16 Kbyte
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
MD_CTR[PPCS] = 1
1000 Hit (supervisor accesses
only)
0100 Hit (user accesses only)
1100 Hit for both
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