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39 lines
838 B
ArmAsm
39 lines
838 B
ArmAsm
; timer routines
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;
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; the timer should be a 16-bit counter that's incremented by about
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; 1000 units per second. it doesn't have to be particularly accurate,
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; if you're working with e.g. a 60 Hz VBLANK IRQ, adding 17 to the
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; counter every frame would be just fine.
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;
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; this is generic timer routines, machine specific code goes in drivers/<machinename>timer.s
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.include "../inc/common.i"
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.export timer_timeout
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.import timer_read
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.bss
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time: .res 2
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.code
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;check if specified period of time has passed yet
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;inputs: AX - maximum number of milliseconds we are willing to wait for
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;outputs: carry flag set if timeout occured, clear otherwise
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timer_timeout:
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pha
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txa
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pha
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jsr timer_read
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stax time
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pla
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tax
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pla
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sec ; subtract current value
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sbc time
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txa
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sbc time + 1
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rts ; clc = timeout, sec = no timeout
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