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

Debug Events
C3.1 About debug events
A debug event can be either:
A Software debug event, see Software debug events on page C3-5
A Halting debug event, see Halting debug events on page C3-38.
A processor responds to a debug event in one of the following ways:
ignores the debug event
takes a debug exception, see Chapter C4 Debug Exceptions
enters Debug state, see Chapter C5 Debug State.
The response depends on the configuration. This is shown in Table C3-1 and in:
Figure C3-1 on page C3-3 for v7 Debug
Figure C3-2 on page C3-4 for v6 Debug and v6.1 Debug.
Configuration Behavior, for specified debug event
Enabled
and
permitted a
DBGDSCR
[15:14] b
BKPT
Instruction
debug event
No xx c Debug
exception d
Yes 00 Debug
exception d
Yes x1 Debug state
entry
Yes 10 Debug
exception
Other Software
debug event
Table C3-1 Processor behavior on debug events
Halting debug
event
Debug-mode
selected and
enabled
Ignore Ignore e Disabled or
not permitted
Ignore Debug state entry f None
Debug state entry Debug state entry Halting
Debug exception or
UNPREDICTABLE g
Debug state entry f Monitor
a. Invasive debug is enabled and the debug event is permitted. Whether a debug event is permitted might depend on the
type of debug event as well as the configuration of the processor, see Chapter C2 Invasive Debug Authentication.
b. See Debug Status and Control Register (DBGDSCR) on page C10-10.
c. The value of DBGSCR[15:14] is ignored when invasive debug is disabled or the debug event is not permitted. If debug
is disabled these bits are RAZ.
d. When debug is disabled or the debug event is not permitted, the BKPT instruction generates a debug exception rather than
being ignored. The DBGDSCR, IFSR and IFAR are set as if a BKPT Instruction debug exception occurred. See Effects
of debug exceptions on CP15 registers and the DBGWFAR on page C4-4.
e. The processor might enter Debug state later, see Halting debug events on page C3-38.
f. In v6 Debug, it is IMPLEMENTATION DEFINED whether the processor enters Debug state or ignores the event.
g. Be careful when programming debug events when Monitor debug-mode is selected and enabled, because certain
conditions can lead to UNPREDICTABLE behavior, see Unpredictable behavior on Software debug events on page C3-24.
In v6 Debug and v6.1 Debug, some events are ignored in this state.
C3-2 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B