Datasheet

207
SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
Table 10-39 shows the AP encodings that define the access permissions for privileged and unprivileged software.
10.23.7 MPU mismatch
When an access violates the MPU permissions, the processor generates a memory management fault, see
“Exceptions and interrupts” on page 61. The MMFSR indicates the cause of the fault. See “Memory Management
Fault Status Register” on page 183 for more information.
10.23.8 Updating an MPU region
To update the attributes for an MPU region, update the RNR, RBAR and RASR registers. You can program each
register separately, or use a multiple-word write to program all of these registers. You can use the RBAR and
RASR aliases to program up to four regions simultaneously using an STM instruction.
10.23.8.1 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
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 you have previously enabled the region being
changed. 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
STRH R3, [R0, #0xA] ; Region Attribute
ORR R2, #1 ; Enable
STRH R2, [R0, #0x8] ; Region Size and Enable
Table 10-39. 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