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

Debug Events
BreakpointDebugEvent()
VectorCatchDebugEvent()
WatchpointDebugEvent()
If the debug event is not permitted, it is ignored by the processor.
Breakpoints and Vector Catches
If invasive debug is enabled, on each instruction the Debug_CheckInstruction() function checks for BRP and
DBGVCR matches. If a match is found the function calls BreakpointDebugEvent() or
VectorCatchDebugEvent(). If the debug event is not permitted, it is ignored by the processor.
On a simple sequential execution model, the Debug_CheckInstruction() call for an instruction occurs just
before the Operation pseudocode for the instruction is executed, and any call it generates to
BreakpointDebugEvent() or VectorCatchDebugEvent() must happen at that time. However, the architecture
does not define when the checks for BRP and DBGVCR matches are made, other than that they must be
made at or before that time. Therefore an implementation can perform the checks much earlier in an
instruction pipeline, marking the instruction as breakpointed, and cause a marked instruction to call
BreakpointDebugEvent() or VectorCatchDebugEvent() if and when it is about to execute.
The BRPMatch() function checks an individual BRP match, calling the BRPLinkMatch() function if necessary
to check whether a linked BRP matches.
The VCRMatch() function checks for a Vector Catch debug event. When vectored interrupt support is enabled,
it uses variables to hold the IRQ and FIQ interrupt vector addresses supplied to the processor by the interrupt
controller on taking an interrupt in IRQ mode or FIQ mode. These variables are updated by the
VCR_OnTakingInterrupt() function, that is called each time the processor takes an IRQ or FIQ interrupt.
For all of these functions, between a context changing operation and an exception entry, exception return or
explicit Instruction Synchronization Barrier (ISB) operation, it is UNPREDICTABLE whether the values of
CurrentModeIsPrivileged(), CPSR.M, CurrentInstrSet(), FindSecure(), and the CONTEXTIDR used by
BRPMatch(), BRPLinkMatch(), and VCRMatch() are the old or the new values.
// Debug_CheckInstruction()
// ========================
Debug_CheckInstruction(bits(32) address, integer length)
// Do nothing if debug disabled.
if DBGDSCR == ‘00’ then return;
case CurrentInstrSet() of
when InstrSet_ARM
step = 4;
when InstrSet_Thumb, InstrSet_ThumbEE
step = 2;
when InstrSet_Jazelle
step = 1;
length = length / step;
vcr_match = FALSE;
brp_match = FALSE;
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