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

The MPU fault checking sequence
Figure B4-2 shows the MPU fault checking sequence, when the MPU is enabled.
Memory address
Alignment
check?
No
B4.4.2 External aborts
Yes
Check address is in a
defined memory region
Address
in a region
?
Yes
No
Check access permissions
Valid
permissions
?
Yes
Access memory
Check address alignment
No
Permission
No No
fault
Protected Memory System Architecture (PMSA)
Does the access require
an alignment check?
Misaligned
?
Background
region
?
Yes
Privileged
access
?
Execution
permitted
?
Alignment
fault
Is use of default memory map as
a Background region enabled?
Figure B4-2 MPU fault checking sequence
External memory errors are defined as errors that occur in the memory system other than those that are
detected by the MPU or Debug hardware. They include parity errors detected by the caches or other parts
of the memory system. An external abort is one of:
synchronous
precise asynchronous
imprecise asynchronous.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. B4-15
Yes
Yes
Yes
No
No
Background
fault
Is access to an XN area in
the Background region?