Debuggers

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1. Why is the memory window update very slow at bad addresses?
2. Why is the local variable window update very slow when the PC is at the beginning of a function?

1. Why is the memory window update very slow at bad addresses?
   A typical BDM transaction between the debugger and the target goes like this:

- Debugger requests a memory-read from target.

- Debugger polls target for end of read.

- Target indicates to debugger that the memory-read is complete.

- Target passes memory-read results to debugger.



The problem is that a memory-read on a bad address causes a bus fault error. A bus fault error looks just like a "memory-read not done" to the debugger's polling routine. So the polling routine must time-out before it can terminate. This time-out takes a long time, resulting in very slow window update speeds. The solution is to scroll the window so that bad memory is not visible.

2. Why is the local variable window update very slow when the PC is at the beginning of a function?
This problem occurs only when the code contains local variable pointers. At the very beginning of a function, the local variables have not been initialized. This usually causes bus faults to occur when the debugger resolves the variable's contents. Bus faults are very slow as explained in a previous FAQ.