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

Non-invasive Debug Authentication
C7.1 About non-invasive debug authentication
Non-invasive debug can be enabled or disabled though the external debug interface. In addition, if a
processor implements the Security Extensions, non-invasive debug operations can be permitted or not
permitted.
The difference between enabled and permitted is that the permitted non-invasive debug operations depend
on both the security state and the operating mode of the processor. The alternatives for when non-invasive
debug is permitted are:
in all processor modes, in both Secure and Non-secure security states
only in Non-secure state
in Non-secure state and in Secure User mode.
Whether non-invasive debug operations are permitted in Secure User mode depends on the value of the
SDER.SUNIDEN bit, see c1, Secure Debug Enable Register (SDER) on page B3-108.
In v6.1 Debug and v7 Debug, non-invasive debug authentication can be controlled dynamically, meaning
that whether non-invasive debug is permitted can change while the processor is running, or while the
processor is in Debug state. However, for more information, see Generation of debug events on page C3-40.
In v6 Debug, non-invasive debug authentication can be changed only while the processor is in reset.
In the recommended external debug interface, the signals that control the enabling and permitting of
non-invasive debug are DBGEN, SPIDEN, NIDEN and SPNIDEN, see Authentication signals on
page AppxA-3.
Part C of this manual assumes that the recommended external debug interface is implemented.
SPIDEN and SPNIDEN are only implemented on processors that implement Security Extensions. NIDEN
is an optional signal in v6 Debug and v6.1 Debug.
Note
DBGEN and SPIDEN also control invasive debug, see About invasive debug authentication on
page C2-2.
In v6 Debug and v6.1 Debug, NIDEN might be implemented on some non-invasive debug
components and not on others. For example, the performance monitoring unit for a processor might
implement NIDEN when the trace macrocell for the same processor does not.
For more information about use of the authentication signals see Changing the authentication signals
on page AppxA-4.
For more information about ARMv6 non-invasive debug see ARMv6 non-invasive debug
authentication on page C7-8.
If both DBGEN and NIDEN are LOW, no non-invasive debug is permitted.
Non-invasive debug authentication in v7 Debug is described in the section v7 Debug non-invasive debug
authentication on page C7-4.
C7-2 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B