Cortex-M3 Processor (Reference Material)
UG0331 User Guide Revision 15.0
126
If the region size is configured to 4GB, in the MPU_RASR, there is no valid ADDR field. In this case, the
region occupies the complete memory map, and the base address is 0x00000000.
The base address is aligned to the size of the region. For example, a 64KB region must be aligned on a
multiple of 64KB, for example, at 0x00010000 or 0x00020000.
3.7.4.5
MPU Region Attribute and Size Register
The MPU_RASR defines the region size and memory attributes of the MPU region specified by the
MPU_RNR, and enables that region and any subregions. See the register summary in
page 123 for its attributes.
MPU_RASR is accessible using word or halfword accesses:
•
the most significant halfword holds the region attributes
•
the least significant halfword holds the region size and the region and subregion enable bits.
The bit assignments are:
Figure 54 •
MPU_RASR Bit Assignments
For information about access permission, refer to
MPU Access Permission Attributes,
Table 82 •
MPU_RASR Bit Assignments
Bits
Name
Function
[31:29]
Reserved.
[28]
XN
Instruction access disable bit:
0: instruction fetches enabled
1: instruction fetches disabled.
[27]
Reserved.
[26:24]
AP
Access permission field, see
[23:22]
Reserved.
[21:19, 17, 16]
TEX, C, B
[18]
S
Shareable bit, see
[15:8]
SRD
Subregion disable bits. For each bit in this field:
0: corresponding sub-region is enabled
1: corresponding sub-region is disabled
See
page 131 for more information.
Region sizes of 128 bytes and less do not support subregions. When writing the
attributes for such a region, write the SRD field as 0x00.
[7:6]
Reserved.
[5:1]
SIZE
Specifies the size of the MPU protection region. The minimum permitted value is 3
(b00010), see See
page 128 for more information.
[0]
ENABLE
Region enable bit.
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