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

Non-invasive Debug Authentication
C7.2 v7 Debug non-invasive debug authentication
On processors that do not implement Security Extensions, if NIDEN is asserted HIGH, non-invasive debug
is enabled and permitted in all modes.
If DBGEN is asserted HIGH the system behaves as if NIDEN is asserted HIGH, regardless of the actual
state of the NIDEN signal.
Table C7-1 shows the required behavior in v7 Debug when the Security Extensions are not implemented.
Table C7-1 v7 Debug non-invasive debug authentication, Security Extensions not
implemented
DBGEN NIDEN Modes in which non-invasive debug is permitted
LOW LOW None. Non-invasive debug is disabled.
x HIGH All modes.
HIGH LOW All modes.
On a processor that implements the Security Extensions:
If both NIDEN and SPNIDEN are asserted HIGH, non-invasive debug is enabled and permitted in
all modes and security states.
If NIDEN is HIGH and SPNIDEN is LOW:
— non-invasive debug is enabled and permitted in Non-secure state
— non-invasive debug is not permitted in Secure privileged modes
— whether non-invasive debug is permitted in Secure User mode depends on the value of the
SDER.SUNIDEN bit.
If DBGEN is HIGH, the system behaves as if NIDEN is HIGH, regardless of the actual state of the NIDEN
signal
If SPIDEN is HIGH, the system behaves as if SPNIDEN is HIGH, regardless of the actual state of the
SPNIDEN signal.
C7-4 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B