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

A.1.2 Run-control and cross-triggering signals
Recommended External Debug Interface
ARM recommends implementation of the run-control and cross-triggering signals EDBGRQ,
DBGTRIGGER, DBGRESTART, and DBGRESTARTED. These signals are particularly useful in a
multiprocessor system, because using them:
A debugger can signal a group of processors to enter Debug state.
A debugger can signal a group of processors to leave Debug state.
A system component can signal a group of processors to enter Debug state when any one of them
enters Debug state because of a debug event on that processor. This is known as cross-triggering.
If you implement the recommended signalling in your system hardware, this signalling means all of the
processors in the group enter or leave Debug state nearly simultaneously.
These signals can also be used in a uniprocessor implementation. For example, debug events not defined by
the debug architecture might be generated externally to the processor. When one of these events occurs the
external system can use these signals to cause the processor to enter Debug state. A trace macrocell might
use these signals in this way.
Contact ARM for details of a recommended Embedded Cross Trigger (ECT) peripheral that you can use in
a multiprocessor system to implement this signalling.
The following subsections describe each of the recommended signals:
EDBGRQ
DBGTRIGGER on page AppxA-6
DBGRESTART and DBGRESTARTED on page AppxA-6.
EDBGRQ
EDBGRQ is the recommended implementation of the External Debug Request mechanism, see Halting
debug events on page C3-38.
EDBGRQ is active-HIGH.
Once EDBGRQ is asserted it must be held HIGH until it is acknowledged:
An implementation can use either DBGACK or DBGTRIGGER to acknowledge EDBGRQ, see:
— DBGACK and DBGCPUDONE on page AppxA-7
— DBGTRIGGER on page AppxA-6.
Alternatively, debugger software might use an IMPLEMENTATION DEFINED method to acknowledge
EDBGRQ. For example, once the processor has entered Debug state the debugger might reprogram
the peripheral that is driving EDBGRQ.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. AppxA-5