ARM922T Technical Reference Manual 3.6. Domain access control

3.6. Domain access control

MMU accesses are primarily controlled through the use of domains. There are 16 domains and each has a 2-bit field to define access to it. Two types of user are supported, clients and managers. The domains are defined in the domain access control register. Figure 3.13 shows how the 32 bits of the register are allocated to define the 16 2-bit domains.

Figure 3.13. Domain access control register format

Table 3.10 defines how the bits within each domain are interpreted to specify the access permissions.

Table 3.10. Interpreting access control bits in domain access control register

Value	Meaning	Description
00	No access	Any access generates a domain fault
01	Client	Accesses are checked against the access permission bits in the section or page descriptor
10	Reserved	Reserved. Currently behaves like the no access mode
11	Manager	Accesses are not checked against the access permission bits so a permission fault cannot be generated

Table 3.11 shows how to interpret the Access Permission (AP) bits and how their interpretation is dependent on the S and R bits (control register bits 8 and 9).

Table 3.11. Interpreting access permission (AP) bits

AP	S	R	Supervisor permissions	User permissions	Description
00	0	0	No access	No access	Any access generates a permission fault
00	1	0	Read-only	No access	Only Supervisor read permitted
00	0	1	Read-only	Read-only	Any write generates a permission fault
00	1	1	Reserved	-	-
01	x	x	Read/write	No access	Access allowed only in Supervisor mode
10	x	x	Read/write	Read-only	Writes in User mode cause permission fault
11	x	x	Read/write	Read/write	All access types permitted in both modes
xx	1	1	Reserved	-	-

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