Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 254

Memory Management Unit
8.7.2 Level-Two Descriptor
Table 8-4 describes the level-two descriptor format supported by hardware.
Resolution Modes," describes the protection modes.)
Bits Name
0–19 RPN Physical (real) page number
20–21 PP Protection
for 1st
subpage
1
22 PP 2nd
subpage
23
24–25 3rd
subpage
26–27 4th
subpage
28 SPS Small page size. Used with the level-one (L1) descriptor's page-size (PS) field; see
"Page Size."
0 4 Kbyte
1 16 Kbyte or larger (512 Kbyte or 8 Mbyte)
29 SH Shared page
0 Entry matches only if a TLB entry's ASID field matches the value in M_CASID.
1 ASID comparison is disabled for the entry.
30 CI Cache-inhibit attribute for the entry.
0 Caching is allowed.
1 Caching is inhibited.
31 V Page valid bit
1
For pages larger than 4 Kbytes in mode 2, PP in bits [22–23,24–25,26–27] must equal the PP in bits [20–21].
8-12
Table 8-4. Level-Two (Page) Descriptor Format
Mode 2
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
MPC885 PowerQUICC Family Reference Manual, Rev. 2
(Section 8.5, "Protection
Mode 1 or Mode 3
For Instruction Pages
Supervisor User
Extended encoding:
00 No access No access
01 Executable No access
1x Reserved
Basic encoding:
00 Executable No access
01 Executable Executable
1x Executable Executable
0 Bits 20–21 contain Basic encoding
1 Bits 20–21 contain extended encoding
C—Change 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, program to the
appropriate subpage
validity. For mode 1,
program to 0b1111.
For Data Pages
Supervisor User
Extended encoding:
00 No access No access
01 R/O No access
1x Reserved
Basic 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 (mode
1 only)
1000 Hit (supervisor
accesses only)
0100 Hit (user accesses
only)
1100 Hit for both
Section 8.7.3,
Freescale Semiconductor