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Memory Management Unit (MMU)
4-10
Freescale Semiconductor
4.3
Functional Description
The ColdFire MMU provides a virtual address, demand-paged memory architecture. The MMU supports
hardware address translation acceleration using software-managed TLBs. It enforces permission checking
on a per-memory request basis, and has control, status, and fault registers for MMU operation.
Table 4-9. MMUDR Field Descriptions
Field
Descriptions
31–10
PA
Physical address. Defines the physical address mapped by this entry. The number of bits used to build the
effective physical address if this TLB entry hits depends on the page size field.
9–8
SZ
Page size. Page size for this entry:
00 1 Mbyte: VA[31–20] used for TLB hit
01 4 Kbytes: VA[31–12] used for TLB hit
10 8 Kbytes: VA[31–13] used for TLB hit
11 16 Mbytes: VA[31–24] used for TLB hit
7–6
CM
Cache mode.
Instruction cache modes:
1
x
Page is non-cacheable.
0
x
Page is cacheable.
Data cache modes:
00 Page is cacheable write-through.
01 Page is cacheable copy-back.
10 Page is non-cacheable precise.
11 Page is non-cacheable imprecise.
5
SP
Supervisor protect. Controls user mode access to the page mapped by this entry.
0 Entry is not supervisor protected.
1 Entry is supervisor protected. An attempted user mode access that matches this entry generates an access
error exception.
4
R
Read access enable. Indicates if data read accesses to this entry are allowed. If a Harvard TLB implementation
is used, this bit is a don’t care for the ITLB. This bit is ignored on writes and always reads as zero for the ITLB.
0 Do not allow data read accesses. Attempted data read accesses that match this entry generate an access error
exception.
1 Allow data-read accesses.
3
W
Write access enable. Indicates if data write accesses are allowed to this entry. If separate ITLB and DTLBs are
used, this bit is a don’t care for the ITLB. This bit is ignored on writes and always reads as zero for the ITLB.
0 Do not allow data write accesses. Attempted data write accesses that match this entry generate an access
error exception.
1 Allow data-write accesses.
2
X
Execute access enable. Indicates if instruction fetches to this entry are allowed. If separate ITLB and DTLBs are
used, this bit is a don’t care for the DTLB. This bit is ignored on writes and reads as zero for the DTLB.
0 Do not allow instruction fetches. Attempted instruction fetches that match this entry cause an access error
exception.
1 Allow instruction-fetch accesses.
1
LK
Lock entry bit. Indicates if this entry is included in the replacement algorithm. TLB hits of locked entries do not
update replacement algorithm information.
0 Include this entry when determining the best entry for a TLB allocation.
1 Do not allow this entry to be selected by the replacement algorithm.
0
Reserved, must be cleared.
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...