Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos

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SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

Use an STM instruction to optimize this:

; R1 = address and region number in one

; R2 = size and attributes in one

LDR R0,=MPU_RBAR    ; 0xE000ED9C, MPU Region Base register

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 register, it must use aligned word accesses



For the MPU_RASR register, 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