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====== Debugging your Program ======

The GameTank emulator contains a few tools to debug your program:

  * The VRAM Viewer allows to check what is actually loaded in VRAM
  * The Memory Browser allows to look at the RAM. Its Variables tab allows to see the value of any global variable defined in C
  * The Code Stepper allows to set breakpoints and execute your program instruction by instruction
  * The Profiler allows to see how much time is being spent by the blitter and the CPU for each screen refresh. In order to keep a 60 FPS animation, the bar shown in the screen should stay well below 1

===== Setting Breakpoints =====

Setting breakpoints in Code Stepper isn't always easy when the program was written in C. Here is a tip to create breakpoints:

  * Define an empty ''breakpoint()'' function
  * Call that function in the areas of your code that need debugging

    void breakpoint() {}
    
    int main () {
       ...
       breakpoint();
       // Doing some stuff that needs to be debugged
       ...
    }

  * In the Code Stepper, set a breakpoint on ''_breakpoint'' (don't forget to enable breakpoints)
  * Step out of the ''breakpoint()'' function
  * Step out of the interrupt handler function
  * You should now be right where you want to be

===== Assembly to C =====

In order to better understand how the assembly code shown in the Code Stepper relates to the original C code:

  * Update the ''makefile'' and add ''--add-source'' to the ''CFLAGS'' value
  * Run ''make build/main.si''
  * Open ''build/main.si''. The original C lines will be inserted as comments, e.g.

  ;
  ; if (tile_val & 0x20) {
  ;
  L000D:	lda     _tile_val
  	and     #$20
  	beq     L000E
  ;
  ; tmp = 1;
  ;
  	lda     #$01
  	sta     _tmp