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

Non-invasive Debug Authentication
C7.4 ARMv6 non-invasive debug authentication
An ARMv6 processor might implement the v7 Debug non-invasive debug authentication signaling
described in v7 Debug non-invasive debug authentication on page C7-4.
In general, non-invasive debug authentication in ARMv6 Debug is IMPLEMENTATION DEFINED. For details
of the implemented authentication scheme you must see the appropriate product documentation. In
particular:
it is IMPLEMENTATION DEFINED whether the NIDEN signal is implemented
the exact roles of the following signals are IMPLEMENTATION DEFINED:
— DBGEN, SPIDEN, and SPNIDEN
— NIDEN, if it is implemented.
However, an ARMv6 non-invasive debug authentication scheme must obey the following rules:
If NIDEN is implemented then tying NIDEN and DBGEN both LOW guarantees that non-invasive
debug is disabled.
if NIDEN is not implemented then the mechanism for disabling non-invasive debug is
IMPLEMENTATION DEFINED. An implementation might not support any mechanism for disabling
non-invasive debug.
When the Security Extensions are implemented, tying SPIDEN and SPNIDEN both LOW
guarantees that non-invasive debug is not permitted in Secure privileged modes.
In addition, if SPIDEN and SPNIDEN are both LOW then setting SDER.SUNIDEN to 0 guarantees
that non-invasive debug is not permitted in Secure User mode.
If non-invasive debug is enabled then if SDER.SUNIDEN is 1, non-invasive debug is permitted in
Secure User mode.
If NIDEN is implemented then tying NIDEN and SPNIDEN both HIGH is guaranteed to enable and
permit non-invasive debug in all modes in both security states.
If NIDEN is not implemented then tying SPNIDEN HIGH is guaranteed to enable and permit
non-invasive debug in all modes in both security states.
Table C7-4 shows the architectural requirements for non-invasive debug behavior in an ARMv6 Debug
implementation that does not include the Security Extensions.
Table C7-4 ARMv6 non-invasive debug authentication requirements, Security Extensions
not implemented
NIDEN DBGEN Non-invasive debug behavior
Implemented and LOW LOW Disabled.
Implemented and HIGH x Enabled.
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