UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 20 December 2013 796 of 841
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 user guide
Use an
STM
instruction to optimize this:
; R1 = region number
; R2 = address
; R3 = size, attributes in one
LDR R0, =MPU_RNR ; 0xE000ED98, MPU region number register
STM R0, {R1-R3} ; Region Number, address, attribute, size and enable
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 Table 684
. 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
34.4.5.8.3 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 Table 685
. 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.
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