Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO Fiche De Données

SAM4E [DATASHEET]

Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14

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 shows the AP encodings that define the access permissions for privileged and unprivileged software.

When an access violates the MPU permissions, the processor generates a memory management fault, see

. The MMFSR indicates the cause of the fault. See 

 for more information.

To update the attributes for an MPU region, update the MPU_RNR, MPU_RBAR and MPU_RASRs. 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.

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

STRH R3, [R0, #0xA]

; Region Attribute

ORR R2, #1

; Enable

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