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
TEX	C	B	S	Memory type	Shareability	Other attributes
b000	0	0	x ¹	Strongly-ordered	Shareable	—
	0	1	x ^a	Device	Shareable	—
	1	0	0	Normal	Not shareable	Outer and inner write-through. No write allocate.
		0	1	Normal	Shareable	Outer and inner write-through. No write allocate.
		1	0	Normal	Not shareable	Outer and inner write-back. No write allocate.
		1	1	Normal	Shareable	Outer and inner write-back. No write allocate.
b001	0	0	0	Normal	Not shareable	Outer and inner non-cacheable.
		0	1	Normal	Shareable	Outer and inner non-cacheable.
		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	1	Normal	Shareable	Outer and inner write-back. Write and read allocate.
b010	0	0	x ^a	Device	Not shareable	Nonshared Device.
	0	1	x ^a	Reserved encoding		—
	1	x ^a	x ^a	Reserved encoding		—
b1BB	A	A	0	Normal	Not shareable	Cached memory², BB = outer policy, AA = inner policy.
b1BB	A	A	1	Normal	Shareable	Cached memory², BB = outer policy, AA = inner policy.

Note:

The MPU ignores the value of this bit.
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 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

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
000	No access	No access	All accesses generate a permission fault
001	RW	No access	Access from privileged software only
010	RW	RO	Writes by unprivileged software generate a permission fault
011	RW	RW	Full access
100	Unpredictable	Unpredictable	Reserved
101	RO	No access	Reads by privileged software only
110	RO	RO	Read only, by privileged or unprivileged software
111	RO	RO	Read only, by privileged or unprivileged software