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

Debug Register Interfaces
Access to all debug registers is not possible if the debug logic is powered down. In this situation:
the system must respond to any access made through the memory-mapped or external debug interface
when the debug power domain is powered down, and ARM recommends that the system generates
an error response
accesses through the coprocessor interface are UNPREDICTABLE.
The debug logic is powered down:
when the debug power domain is powered down, in an implementation with separate debug and core
power domains
when the processor is powered down, in a SinglePower implementation.
C6.5.4 Access to IMPLEMENTATION DEFINED and reserved registers
The following subsections describe the responses to accesses to IMPLEMENTATION DEFINED and reserved
registers:
Access to implementation defined registers
Access to reserved registers on page C6-30.
Note
There are no IMPLEMENTATION DEFINED or reserved registers in the Baseline CP14 interface and therefore
these sections do not say anything about accesses through the Baseline CP14 interface.
Any unused registers in the spaces for IMPLEMENTATION DEFINED registers must behave as reserved
registers. These spaces are register numbers 512-575 and 928-959.
Access to IMPLEMENTATION DEFINED registers
When the Debug Software Enable function, described in Permissions in relation to locks on page C6-27, is
disabling software access to the debug registers, Table C6-3 shows how the response to an accesses to an
IMPLEMENTATION DEFINED register depends on the debug interface used for the access.
Table C6-3 Accesses to IMPLEMENTATION DEFINED registers when
Debug Software Enable disables access
Debug interlace used for access a
Response
Memory-mapped interface Error response
Extended CP14 interface Undefined Instruction exception
External debug interface IMPLEMENTATION DEFINED
a. There are no IMPLEMENTATION DEFINED registers in the Baseline CP14
interface.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. C6-29