10-16
ColdFire CF4E Core User’s Manual
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MMU Definition
MMUTR and MMUDR. TLB write accesses place MMUTR and MMUDR contents into
the TLB tag and data entries defined by the allocation address or MMUAR.
MMUTR, Figure 10-8, contains the virtual address tag, the address space ID (ASID), a
shared page indicator, and the valid bit.
Table 10-9 describes MMUTR fields.
MMUDR, Figure 10-9, contains the physical address, cache mode field, page size,
supervisor-protect bit, read, write, execute permission bits, and lock-entry bit.
Table 10-9 describes MMUDR fields.
31
10
9
2
1
0
Field
VA
ID
SG V
Reset
—
R/W
R/W
Rc
0x0014
Figure 10-8. MMU Read/Write TLB Tag Register (MMUTR)
Table 10-9. MMUTR Field Descriptions
Bits
Name
Description
31–10
VA
Virtual address. Defines the virtual address mapped by this entry. The number of bits used in the TLB
hit determination depends on the page size field in the corresponding TLB data entry.
9–2
ID
Address space ID (ASID). This extension to the virtual address marks this entry as part of 1 of 256
possible address spaces. Address space 0x00 can be reserved for supervisor mode. The other 255
address spaces are used to tag user processes. TLB entry ASID values are compared to the ASID
register value for user mode unless the TLB entry is marked shared (SG = 1). The TLB entry ASID
value may be compared to 0x00 for supervisor accesses or to the ASID. The description of
MMUCR[ASM] in Table 10-5 gives details on supervisor mode and ASID compares.
1
SG
Shared global. Indicates when the entry is shared among user address spaces. If an entry is shared,
its ASID is not part of the TLB hit determination for user accesses.
0 This entry is not shared globally.
1 This entry is shared globally.
Note that the ASID can be used to determine supervisor mode hits to allow two sharing levels. If SG
and MMUCR[ASM] are set and the ASID is not zero, all users (but not the supervisor) share an entry.
If SG and MMUCR[ASM] are set and the ASID is zero, all users and the supervisor share an entry.
The description of ASM in Table 10-5 details supervisor mode and ASID compares.
0
V
Valid. Indicates when the entry is valid. Only valid entries generate a TLB hit.
0 Entry is not valid.
1 Entry is valid.
31
10
9
8
7
6
5
4
3
2
1
0
Field
PA
SZ
CM
SP R W X LK —
Reset
—
R/W
R/W
Rc
0x0018
Figure 10-9. MMU Read/Write TLB Data Register
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