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

Debug Exceptions
C4.1 About debug exceptions
A debug exception is taken when:
a permitted Software debug event occurs when invasive debug is enabled and Monitor debug-mode
is selected
a BKPT instruction is executed when one of:
— invasive debug is disabled
— the debug event is not permitted
— no debug-mode is selected.
For more information, see Table C3-1 on page C3-2. You must be careful when programming certain events
because you might leave the processor in an unrecoverable state. See Unpredictable behavior on Software
debug events on page C3-24.
How the processor handles the debug exception depends on the cause of the exception, and is described in:
Debug exception on Breakpoint, BKPT Instruction or Vector Catch debug events
Debug exception on Watchpoint debug event on page C4-3.
Halting debug events never cause a debug exception. The Halting debug events are:
External Debug Request debug event
Halt Request debug event
OS Unlock Catch debug event.
C4.1.1 Debug exception on Breakpoint, BKPT Instruction or Vector Catch debug events
If the cause of the debug exception is a Breakpoint, BKPT Instruction, or a Vector Catch debug event, the
processor performs the following actions:
Sets the DBGDSCR.MOE bits according to Table C10-3 on page C10-26.
Sets the IFSR and IFAR as described in Effects of debug exceptions on CP15 registers and the
DBGWFAR on page C4-4.
Generates a Prefetch Abort exception, see Prefetch Abort exception on page B1-54
The Prefetch Abort handler is responsible for checking the IFSR bits to find out whether the exception entry
was caused by a debug exception. If it was, typically the handler branches to the debug monitor.
C4-2 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B