Atmel SAM4S Series, Предварительный информационный лист

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11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
Table 11-37
shows the AP encodings that define the access permissions for privileged and
unprivileged software.
11.11.1.1 MPU Mismatch
When an access violates the MPU permissions, the processor generates a memory manage-
ment fault, see
“Exceptions and Interrupts” . The MMFSR indicates the cause of the fault. See
“MMFSR: Memory Management Fault Status Subregister” for more information.
11.11.1.2 Updating 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.
11.11.1.3 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
01 Write back, write and read allocate
10 Write through, no write allocate
11 Write back, no write allocate
Table 11-37. 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
Table 11-36. Cache Policy for Memory Attribute Encoding (Continued)
Encoding, AA or BB Corresponding Cache Policy