Cortex-M3 Processor (Reference Material)
UG0331 User Guide Revision 15.0
128
The following table describes the cache policy for memory attribute encodings with a TEX value is in the
range 4-7.
The following table lists the AP encodings that define the access permissions for privileged and
unprivileged software.
3.7.4.7
MPU Mismatch
When an access violates the MPU permissions, the processor generates a MemManage fault, see
page 28. The MMFSR indicates the cause of the fault. See
page 119 for more information.
3.7.4.8
Updating an MPU Region
To update the attributes for an MPU region, update the MPU_RNR, MPU_RBAR and MPU_RASR
registers. You can program each register separately, or use a multiple-word write to program all of these
registers. You can use the MPU_RBAR and MPU_RASR aliases to program up to four regions
simultaneously using an STM instruction.
Updating an MPU region using separate words
Simple code to configure one region:
; R1 = region number
; R2 = size/enable
; R3 = attributes
; R4 = address
LDR R0,=MPU_RNR
; 0xE000ED98, MPU region number register
STR R1, [R0, #0x0]
; Region Number
STR R4, [R0, #0x4]
; Region Base Address
Table 85 •
Cache Policy for Memory Attribute Encoding
Encoding, AA or BB Corresponding cache policy
00
Non-cacheable
01
Write back, write and read
allocate
10
Write through, no write allocate
11
Write back, no write allocate
Table 86 •
AP Encoding
AP[2:0]
Privileged
Permissions
Unprivileged
Permissions
Description
000
No access
No access
All accesses generate a permission fault
001
RW
No access
Access from privileged software only
010
RW
RO
Writes by unprivileged software generate a permission fault
011
RW
RW
Full access
100
Unpredictable
Unpredictable
Reserved
101
RO
No access
Reads by privileged software only
110
RO
RO
Read only, by privileged or unprivileged software
111
RO
RO
Read only, by privileged or unprivileged software
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