Debug Interface Signals - ARM ARM966E-S Technical Reference Manual

8.4

Debug interface signals

8.4.1 Entry into debug state on breakpoint
ARM DDI 0186A
There are four primary external signals associated with the debug interface:
• DBGIEBKPT, DBGDEWPT, and EDBGRQ are system requests for the
ARM966E-S to enter debug state
• DBGACK is used by the ARM966E-S to flag back to the system that it is in
debug state.
Any instruction being fetched from memory is sampled at the end of a cycle. To apply
a breakpoint to that instruction, the breakpoint signal must be asserted by the end of the
same cycle. This is shown in Figure 8-4 on page 8-10.
You can build External logic, such as additional breakpoint comparators, to extend the
breakpoint functionality of the EmbeddedICE-RT logic. These outputs must be applied
to the DBGIEBKPT input. This signal is ORed with the internally-generated
breakpoint signal before being applied to the ARM9E-S core control logic. The timing
of the input makes it unlikely that data-dependent external breakpoints are possible.
A breakpointed instruction is allowed to enter the Execute stage of the pipeline, but any
state change as a result of the instruction is prevented. All writes from previous
instructions complete as normal.
The Decode cycle of the debug entry sequence occurs during the Execute cycle of the
breakpointed instruction. The latched breakpoint signal forces the processor to start the
debug sequence.
Figure 8-4 on page 8-10 shows breakpoint timing.
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Debug Support
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