emailler/client/ip65/timer.s

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; 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,
; if you're working with e.g. a 60 Hz VBLANK IRQ, adding 17 to the
; counter every frame would be just fine.
;
; this is generic timer routines, machine specific code goes in drivers/<machinename>timer.s
.include "../inc/common.i"
.export timer_timeout
.import timer_read
.bss
time: .res 2
.code
;check if specified period of time has passed yet
;inputs: AX - maximum number of milliseconds we are willing to wait for
;outputs: carry flag set if timeout occured, clear otherwise
timer_timeout:
pha
txa
pha
jsr timer_read
stax time
pla
tax
pla
sec ; subtract current value
sbc time
txa
sbc time + 1
rts ; clc = timeout, sec = no timeout