Cortex-M3 Processor (Reference Material)
UG0331 User Guide Revision 15.0
127
3.7.4.5.1
SIZE Field Values
The SIZE field defines the size of the MPU memory region specified by the MPU_RNR. as follows:
(Region size in bytes) = 2(SIZE+1)
The smallest permitted region size is 32B, corresponding to a SIZE value of 4. The following table
provides example SIZE values, with the corresponding region size and value of N in the MPU_RBAR.
3.7.4.6
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 83 •
Example SIZE Field Values
SIZE value
Region size
Value of N
1
1.
In the MPU_RBAR, see
MPU Region Base Address Register,
Note
b00100 (4)
32B
5
Minimum permitted size
b01001 (9)
1KB
10
b10011 (19)
1MB
20
b11101 (29)
1GB
30
b11111 (31)
4GB
32
Maximum possible size
Table 84 •
TEX, C, B, and S Encoding
TEX
C
B
S
Memory type
Shareability
Other attributes
b000
0
0
x
1
1.
The MPU ignores the value of this bit.
Strongly-ordered
Shareable
1
x
a
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 non-cacheable.
1
Shareable
1
x
a
Reserved encoding
1
0
x
a
Implementation defined attributes.
1
0
Normal
Not shareable
Outer and inner write-back. Write and read
allocate.
1
Shareable
b010
0
0
x
a
Device
Not shareable
Nonshared Device.
1
x
a
Reserved encoding
1
x
a
x
a
Reserved encoding
b1BB
A
A
0
Normal
Not shareable
Cached memory
2
, BB = outer policy,
AA = inner policy.
2.
See
page 129 for the encoding of the AA and BB bits.
1
Shareable