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 793 of 841
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 user guide
34.4.5.6 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 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.
Table 687
shows the encodings for the TEX, C, B, and S access permission bits.
[1] The MPU ignores the value of this bit.
[2] See Table 688
for the encoding of the AA and BB bits.
Table 688 shows the cache policy for memory attribute encodings with a TEX value is in
the range 4-7.
Table 689 shows the AP encodings that define the access permissions for privileged and
unprivileged software.
Table 687. TEX, C, B, and S encoding
TEX C B S Memory type Shareability Other attributes
b000 0
0 x
[1]
Strongly-ordered Shareable -
1 x
[1]
Device Shareable -
1 0 0 Normal Not shareable Outer and inner write-through.
No write allocate.
1 Shareable
1 0 Normal Not shareable Outer and inner write-back. No
write allocate.
1 Shareable
b001 0
0 0 Normal Not shareable Outer and inner noncacheable.
1 Shareable
1 x
[1]
Reserved encoding -
1 0 x
[1]
Implementation defined attributes. -
1 0 Normal Not shareable Outer and inner write-back. Write
and read allocate.
1 Shareable
b010 0 0 x
[1]
Device Not shareable Nonshared Device.
1 x
[1]
Reserved encoding -
1x
[1]
x
[1]
Reserved encoding -
b1BB A A 0 Normal Not shareable Cached memory
[2]
, BB = outer
policy, AA = inner policy.
1 Shareable
Table 688. Cache policy for memory attribute encoding
Encoding, AA or BB Corresponding cache policy
00 Non-cacheable
01 Write back, write and read allocate
10 Write through, no write allocate
11 Write back, no write allocate
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