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13.9
Debug exception
ARM DDI 0301H
ID012310
When a Software debug event occurs and Monitor debug-mode is selected and enabled and the
core is in a state that permits debug then a Debug exception is taken. Prefetch Abort and Data
Abort Vector catch debug events are ignored though. Unlinked context ID and any IMVA
mismatch breakpoint debug events are also ignored if the processor is running in a privileged
mode and Monitor debug-mode is selected and enabled. If the cause of the Debug exception is
a watchpoint debug event, the processor performs the following actions:
•
The DSCR[5:2] method of entry bits are set to indicate that a watchpoint occurred.
•
The CP15 DFSR, FAR, and WFAR are set as Effect of a debug event on CP15 registers
on page 13-34 describes.
•
The same sequence of actions as in a Data Abort exception is performed. This includes
setting the R14_abt, base register and destination registers to the same values as if this was
a Data Abort.
The Data Abort handler is responsible for checking the DFSR bit to determine if the routine
entry was caused by a debug exception or a Data Abort exception. On entry:
1.
It must first check for the presence of a debug monitor target.
2.
If present, the handler must disable the active watchpoints. This is necessary to prevent
corruption of the FAR because of an unexpected watchpoint debug event when servicing
a Data Abort exception.
3.
If the cause is a Debug exception the Data Abort handler branches to the debug monitor
target.
Note
•
the watchpointed address can be found in the FAR
•
the address of the instruction that caused the watchpoint debug event can be found
in the WFAR
•
the address of the instruction to restart at plus
register.
If the cause of the Debug exception is a breakpoint, software breakpoint or vector catch debug
event, the processor performs the following actions:
•
the DSCR[5:2] method of entry bits are set appropriately
•
the CP15 IFSR register is set as Effect of a debug event on CP15 registers on page 13-34
describes.
•
the same sequence of actions as in a Prefetch Abort exception is performed.
The Prefetch Abort handler is responsible for checking the IFSR bits to find out if the routine
entry is caused by a Debug exception or a Prefetch Abort exception. If the cause is a Debug
exception it branches to the debug monitor target.
Note
The address of the instruction causing the Software debug event plus
R14_abt register.
Table 13-24 on page 13-36 lists the values in the link register after exceptions.
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0x08
can be found in the R14_abt
can be found in the
0x04
Debug
13-35
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