Hello Venki,
Within your code snippet, there are tests for a total of five different timing events, presumably the result of a periodic timer interrupt.
The first timing event utilises a word value at RAM address $45, used as a counter, and a further word value at $47 that contains the address of a sub-routine to be executed in the event of timeout. The contents of these registers will have been setup elsewhere within the program, likely outside of the interrupt code. You will need to search for the other locations that write to these registers to identify what the timing events actually mean.
The processing of the timing event -
- Test counter value ($45/$46), and if non-zero, decrement the value - otherwise skip to next event.
- Test new counter value, and if zero (timeout), continue with current event - otherwise skip to next event.
- Test sub-routine address value ($47/$48), and if zero (invalid address), skip to next event.
- Execute sub-routine (JSR ,X).
Each timing event follows a similar pattern, although the code is not quite identical, presumably because of the compiled C origins.
Regards,
Mac