Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO Data Sheet

SAM4E [DATASHEET]

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

268

STM R0, {R1-R2}

; Region base address, region number and VALID bit,

; and Region Attribute, Size and Enable

Regions of 256 bytes or more are divided into eight equal-sized subregions. Set the corresponding bit in the SRD
field of the MPU_RASR field to disable a subregion. See 

. The least

significant bit of SRD controls the first subregion, and the most significant bit controls the last subregion. Disabling
a subregion means another region overlapping the disabled range matches instead. If no other enabled region
overlaps the disabled subregion, the MPU issues a fault. 

Regions of 32, 64, and 128 bytes do not support subregions. With regions of these sizes, the SRD field must be
set to 0x00, otherwise the MPU behavior is unpredictable.

Two regions with the same base address overlap. Region 1 is 128 KB, and region 2 is 512 KB. To ensure the
attributes from region 1 apply to the first 128 KB region, set the SRD field for region 2 to b00000011 to disable the
first two subregions, as in 

 below:

To avoid unexpected behavior, disable the interrupts before updating the attributes of a region that the interrupt
handlers might access.

Ensure the software uses aligned accesses of the correct size to access MPU registers:



Except for the MPU_RASR, it must use aligned word accesses



For the MPU_RASR, it can use byte or aligned halfword or word accesses.

The processor does not support unaligned accesses to MPU registers.

When setting up the MPU, and if the MPU has previously been programmed, disable unused regions to prevent
any previous region settings from affecting the new MPU setup.

Region 1

Disabled subregion

Disabled subregion

Region 2, with 

subregions

Base address of both regions

Offset from
base address

0

64KB

128KB

192KB

256KB

320KB

384KB

448KB

512KB