Memory Management Unit
3-24 Copyright © 2001-2003 ARM Limited. All rights reserved. ARM DDI0198D
3.4 Domain access control
MMU accesses are primarily controlled through the use of domains. There are 16
domains and each has a two-bit field to define access to it. Two types of user are
supported:
• clients
• managers.
The domains are defined in the domain access control register, CP15 c3. Figure 2-7 on
page 2-18 shows how the 32 bits of the register are allocated to define the 16 two-bit
domains.
Table 3-11 defines how the bits within each domain are interpreted to specify the access
permissions.
Table 3-12 shows how to interpret the Access Permission (AP) bits and how their
interpretation is dependent on the R and S bits (Control Register c1 bits [9:8]).
Table 3-11 Domain access control register, access control bits
Value Meaning Description
0 0 No access Any access generates a domain fault.
0 1 Client Accesses are checked against the access permission bits in
the section or page descriptor.
1 0 Reserved Reserved. Currently behaves like the no access mode.
1 1 Manager Accesses are not checked against the access permission
bits so a permission fault cannot be generated.
Table 3-12 Interpreting access permission (AP) bits
AP S R Privileged permissions User permissions
0 0 0 0 No access No access
0 0 1 0 Read-only No access
0 0 0 1 Read-only Read-only
0 0 1 1 Unpredictable Unpredictable
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