9.12.6. System speed accesses

If a system speed access is performed during debug state, the value of the PC is increased by five addresses. Because system speed instructions access the memory system, it is possible for aborts to take place. If an abort occurs during a system speed memory access, the ARM9TDMI core enters abort mode before returning to debug state.

This is similar to an aborted watchpoint. However, the problem is much harder to fix because the abort is not caused by an instruction in the main program, and the PC does not point to the instruction that caused the abort. An abort handler usually looks at the PC to determine the instruction that caused the abort, and therefore the abort address. In this case, the value of the PC is invalid, but the debugger knows the address of the location being accessed. Therefore the debugger can be written to help the abort handler fix the memory system.

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