2.7.4.6 MPU Access Permission Attributes

This section describes the MPU access permission attributes. The access permission bits, TEX, C, B, S, AP, and XN, of the MPU_RASR, control access to the corresponding memory region. If an access is made to an area of memory without the required permissions, then the MPU generates a permission fault.

The following table shows the encodings for the TEX, C, B, and S access permission bits.

Table 2-78. TEX, C, B, and S Encoding
TEXCBSMemory typeShareabilityOther attributes
b00000x 1Strongly-orderedShareable
1x aDeviceShareable
100NormalNot shareableOuter and inner write-through. No write allocate.
1Shareable
10NormalNot shareableOuter and inner write-back. No write allocate.
1Shareable
b001000NormalNot shareableOuter and inner non-cacheable.
1Shareable
1x aReserved encoding
10x aImplementation defined attributes.
10NormalNot shareableOuter and inner write-back. Write and read allocate.
1Shareable
b01000x aDeviceNot shareableNonshared Device.
1x aReserved encoding
1x ax aReserved encoding
b1BBAA0NormalNot shareableCached memory2, BB = outer policy, AA = inner policy.
1Shareable
Note:
  1. The MPU ignores the value of this bit.
  2. See Table 2-79 for the encoding of the AA and BB bits.

The following table describes the cache policy for memory attribute encodings with a TEX value is in the range 4-7.

Table 2-79. Cache Policy for Memory Attribute Encoding
Encoding, AA or BBCorresponding cache policy
00Non-cacheable
01Write back, write and read allocate
10Write through, no write allocate
11Write back, no write allocate

The following table lists the AP encodings that define the access permissions for privileged and unprivileged software.

Table 2-80. AP Encoding
AP[2:0]Privileged

Permissions

Unprivileged

Permissions

Description
000No accessNo accessAll accesses generate a permission fault
001RWNo accessAccess from privileged software only
010RWROWrites by unprivileged software generate a permission fault
011RWRWFull access
100UnpredictableUnpredictableReserved
101RONo accessReads by privileged software only
110RORORead only, by privileged or unprivileged software
111RORORead only, by privileged or unprivileged software