; timer routines
;
; the timer should be a 16-bit counter that's incremented by about
; 1000 units per second. it doesn't have to be particularly accurate.

	.include "../inc/common.i"


	.export timer_init
	.export timer_read
  
	.code
  
; initialize timers
timer_init:
	lda #$80		; stop timers
	sta $dd0e
	sta $dd0f

	ldax #999		; timer A to 1000 cycles
	stax $dd04

	ldax #$ffff		; timer B to max cycles
	stax $dd06

	lda #$81		; timer A in continuous mode
	sta $dd0e

	lda #$c1		; timer B to count timer A underflows
	sta $dd0f

	rts


; return the current value
timer_read:
	lda $dd07		; cia counts backwards, return inverted value
	eor #$ff
	tax
	lda $dd06
	eor #$ff
	rts