timers.a65

.include "timers.h"

.zeropage
FrameCounter: .res 1

.bss
Timers:
	.tag RT
	.tag LT 
LongSubTimer: .res 1
Pretimer: .res 1

.segment "MAIN"
.proc Tick
	lda Pretimer	;if master timer control not set, decrement
	beq DecTimers	;all frame and interval timers
	dec Pretimer
	bne NoDecTimers

DecTimers:
	ldx #.sizeof(RT) - 1	;load end offset for end of frame timers
	dec LongSubtimer	;decrement interval timer control,
	bpl @Do	;if not expired, only frame timers will decrement
	lda #LongSubtimerFrames - 1
	sta LongSubtimer 	;if control for interval timers expired,
	ldx #.sizeof(RT) + .sizeof(LT) - 1	;interval timers will decrement along with frame timers

@Do: 
	lda Timers,x	;check current timer
	beq @Continue 	;if current timer expired, branch to skip,
	dec Timers,x	;otherwise decrement the current timer

@Continue:
	dex	;move onto next timer
	bpl @Do	;do this until all timers are dealt with

NoDecTimers:
	inc FrameCounter	;increment frame counter
	rts
.endproc