ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Bn, bit [n], for n = 0 to 7
Bufferability bit, B, for memory protection region n.
Accessing the Memory Region Bufferability Register
ARMv4 and ARMv5 Differences
To access the Memory Region Bufferability Register you read or write the CP15 registers with set to
0, set to c3, set to c0, and set to 0. For example:
MRC p15,0,,c3,c0,0 ; Read CP15 Data or unified Region Bufferability Register
MCR p15,0,,c3,c0,0 ; Write CP15 Data or unified Region Bufferability Register
c5, Memory Region Access Permissions Registers (DAPR and IAPR)
The two Memory Region Access Permissions Registers are:
The Data or unified Access Permissions Register, DAPR.
The Instruction Access Permissions Register, IAPR. The IAPR is implemented only when the
processor implements separate data and instruction memory protection region definitions.
A Memory Region Access Permissions Register hold the access permission bits AP[1:0] for each of the
eight memory protection regions.
The format of a Memory Region Access Permissions Register is:
31 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Reserved AP7 AP6 AP5 AP4 AP3 AP2 AP1 AP0
Bits [31:16] Reserved. UNK/SBZP.
APn, bits [2n+1:2n], for n = 0 to 7
Access permission bits AP[1:0] for memory protection region n.
For details of the significance and encoding of these bits see Table H-10 on page AppxH-29.
If the implementation does not permit the requested type of access, it signals an abort to the processor.
Accessing the Memory Region Access Permissions Registers
To access the Memory Region Access Permissions Registers you read or write the CP15 registers with
set to 0, set to c5, set to c0, and set as follows:
0 if there is only a single set of protection regions
when there are separate memory protection regions for data and instructions:
— 0 to access the Data Region Access Permissions Register
— 1 to access the Instruction Region Access Permissions Register.
For example:
MRC p15,0,,c5,c0,0 ; Read CP15 Data or unified Region Access Permissions Register
MCR p15,0,,c5,c0,0 ; Write CP15 Data or unified Region Access Permissions Register
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. AppxH-45