Datasheet

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SAM4S [DATASHEET]
11100E–ATARM–24-Jul-13
Table 12-37 shows the AP encodings that define the access permissions for privileged and unprivileged software.
12.11.1.1MPU Mismatch
When an access violates the MPU permissions, the processor generates a memory management fault, see “Exceptions
and Interrupts” . The MMFSR indicates the cause of the fault. See “MMFSR: Memory Management Fault Status
Subregister” for more information.
12.11.1.2Updating an MPU Region
To update the attributes for an MPU region, update the MPU_RNR, MPU_RBAR and MPU_RASR registers. Each
register can be programed separately, or a multiple-word write can be used to program all of these registers.
MPU_RBAR and MPU_RASR aliases can be used to program up to four regions simultaneously using an STM
instruction.
12.11.1.3Updating 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
STRH R2, [R0, #0x8] ; Region Size and Enable
STRH R3, [R0, #0xA] ; Region Attribute
Disable a region before writing new region settings to the MPU, if the region being changed was previously enabled. For
example:
; 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
BIC R2, R2, #1 ; Disable
STRH R2, [R0, #0x8] ; Region Size and Enable
STR R4, [R0, #0x4] ; Region Base Address
Table 12-37. 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