PM0214 datasheet(183/245 Pages) STMICROELECTRONICS

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PM0214

Core peripherals

244

You can do this in two words for pre-packed information. This means that the RBAR

contains the required region number and had the VALID bit set to 1, see MPU region base

address register (MPU_RBAR) on page 188. Use this when the data is statically packed, for

example in a boot loader:

; R1 = address and region number in one

; R2 = size and attributes in one

LDR R0, =MPU_RBAR

; 0xE000ED9C, MPU Region Base register

STR R1, [R0, #0x0]

; Region base address and

; region number combined with VALID (bit 4) set to 1

STR R2, [R0, #0x4]

; Region Attribute, Size and Enable

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

Subregions

Regions of 256 bytes or more are divided into eight equal-sized subregions. Set the

corresponding bit in the SRD field of the RASR to disable a subregion, see Section 4.2.9:

MPU region attribute and size register (MPU_RASR) on page 189. 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,

you must set the SRD field to 0x00, otherwise the MPU behavior is Unpredictable.

Example of SRD use:

Two regions with the same base address overlap. Region one is 128KB, and region two is

512KB. To ensure the attributes from region one apply to the first128KB region, set the SRD

field for region two to b00000011 to disable the first two subregions, as the figure shows.

Figure 18. Subregion example

Region 1

Disabled subregion

Region 2, with

subregions

Base address of both regions

Offset from

base address

64KB

128KB

192KB

256KB

320KB

384KB

448KB

512KB

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