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Debug in Depth

0 E1A00000; MOV R0, R0

1 E1A00000; MOV R0, R0

0 EAFFFFFA; B -6

This code restores the PC and restarts the program from the next instruction.

B.9.5 System speed access

When a system-speed access is performed during debug state, the value of the PC

increases by three addresses. System speed instructions access the memory system and

so it is possible for aborts to take place. If an abort occurs during a system-speed

memory access, the ARM7TDMI core enters abort mode before returning to debug

state.

This is similar to an aborted watchpoint, but the problem is much harder to fix because

the abort was not caused by an instruction in the main program and so 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 also the abort address. In this case,

the value of the PC is invalid, but because the debugger can determine which location

was being accessed, the debugger can be written to help the abort handler fix the

memory system.

B.9.6 Summary of return address calculations

The calculation of the branch return address is as follows:

• for normal breakpoint and watchpoint, the branch is:

- (4+N+3S)

• for entry through debug request (DBGRQ) or watchpoint with exception, the

branch is:

- (3+N+3S)

where N is the number of debug-speed instructions executed, including the final branch,

and S is the number of system-speed instructions executed.

Brand

Model

ARM7TDMI

ARM ARM7TDMI User Manual

Other manuals for ARM ARM7TDMI