How to Use Breakpoints

• To skip over a long running correct part of the program to get to the part with a bug.

  For example, your program has a bug after a long running loop (e.g., a for loop with an index running from 1 to 10 or more) which is correct. To get to the program part with the bug quickly do this:

  • Place a label - say X - at the first instruction following the loop,

  • xdef the label X at the very beginning of the program

  • Assemble the program.

  • Start Egtapi and set a breakpoint at X using the Add button in the break point window.

  • Now run Egtapi, and it will stop the instruction that is labeled with the label X.

    Note: if Egtapi does not stop there, then your program must not have reached the instruction labeled by X and you have made a terrible logical error in your program....

    From this point onward, use Single Step button to execute the instructions in the suspect part to find your bug.

    Make sure you watch all relevant registers and variables (in the variable watch section) to provide you with necessary information to find the bug.

• To find a bug in a loop.

  One of the common bugs is a loop where it works for the first N time through and it fails to work for the N+1 time.

  To find what is wrong with the N+1 time thorugh the loop, we must go through the first N times very quickly (it is a waste of time to watch something that is correct).

  This will help you get through the first N times of the loop quickly:

  • Place a label - say X - at the start of the loop,

  • xdef the label X and set a breakpoint at X with Egtapi.

  • Now run the program until it stops at label X.

  • Now press the Continue button for N times - Egtapi will always stop at the instruction marked by label X.

    (So we are skipping over the first N times through the loop which is when the program ran correctly).

  • When it stopped for the N time at label X, use the Single Step button to execute the instructions of the loop one at a time and watch the registers and variables carefully to find the bug.

    Make sure you display all relevant variables in the variable watch window that will provide you with necessary information to find the bug.