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 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

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