Functional Peripherals Description
85
SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Cortex-M4F Peripherals
When setting up the MPU, and if the MPU has previously been programmed, disable unused regions to
prevent any previous region settings from affecting the new MPU setup.
2.2.4.1
MPU Access Permission Attributes
The access permission bits, TEX, S, C, B, AP, and XN of the RASR register, 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.
shows the encodings for the TEX, C, B, and S access permission bits. All encodings are shown
for completeness, however the current implementation of the Cortex-M4 does not support the concept of
cacheability or shareability. Refer to
for information on programming the MPU.
(1)
The MPU ignores the value of this bit.
Table 2-2. TEX, S, C, and B Bit Field Encoding
TEX
S
C
B
Memory type
Shareability
Other attributes
000b
x
(1)
0
0
Strongly Ordered
Shareable
-
000b
x
(1)
0
1
Device
Shareable
-
000b
0
1
0
Normal
Not shareable
Outer and inner write-through. No write
allocate.
000b
1
1
0
Normal
Shareable
000b
0
1
1
Normal
Not shareable
000b
1
1
1
Normal
Shareable
001b
0
0
0
Normal
Not shareable
Outer and inner noncacheable.
001b
1
0
0
Normal
Shareable
001b
x
(1)
0
1
Reserved encoding
-
-
001b
x
(1)
1
0
Reserved encoding
-
-
001b
0
1
1
Normal
Not shareable
Outer and inner write-back. Write and
read allocate.
001b
1
1
1
Normal
Shareable
010b
x
(1)
0
0
Device
Not shareable
Nonshared Device.
010b
x
(1)
0
1
Reserved encoding
-
-
010b
x
(1)
1
x
(1)
Reserved encoding
-
-
1BB
0
A
A
Normal
Not shareable
Cached memory , BB = outer policy,
AA = inner policy.
See
for the encoding of the AA
and BB bits.
1BB
1
A
A
Normal
Shareable
shows the cache policy for memory attribute encodings with a TEX value in the range of 0x4-
0x7.
Table 2-3. 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
shows the AP encodings in the RASR register that define the access permissions for privileged
and unprivileged software.
Table 2-4. AP Bit Field Encoding
AP Bit Field
Privileged
Permissions
Unprivileged
Permissions
Description
000
No access
No access
All accesses generate a permission fault.