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13.6.4. Behavior of the processor on debug events

This section describes how the processor behaves on debug events while not in debug state. See Debug state for information on how the processor behaves while in debug state.

When a software debug event occurs and Monitor debug-mode is selected and enabled then a Debug exception is taken. However, Prefetch Abort and Data Abort Vector catch debug events are ignored. This is to avoid the processor ending in an unrecoverable state on certain combinations of exceptions and vector catches. Unlinked context ID breakpoint debug events are also ignored if the processor is running in a privileged mode and Monitor debug-mode is selected and enabled.

The external debug request signal and the Halt DBGTAP instruction are ignored when Monitor debug-mode is selected and enabled.

When a debug event occurs and Halt mode is selected and enabled then the processor enters debug state.

When neither Halt nor Monitor debug-mode is selected and enabled, all debug events are ignored, although the BKPT instruction generates a Prefetch Abort exception.

Behavior of the processor on debug events
DSCR[15:14]Mode selected and enabledAction on software debug eventAction on external debug request signal activationAction on Halt DBGTAP
b00NoneIgnore/Prefetch Abort[1]IgnoreIgnore
b01HaltDebug state entryDebug state entryDebug state entry
b10MonitorDebug exception/Ignore[2]IgnoreIgnore
b11HaltDebug state entryDebug state entryDebug state entry

[1] When debug is disabled, a BKPT instruction generates a Prefetch Abort exception instead of being ignored.

[2] Prefetch Abort and Data Abort vector catch debug events are ignored in Monitor debug-mode. Unlinked context ID breakpoint debug events are also ignored if the processor is running in a privileged mode and Monitor debug-mode is selected and enabled.