25 lines
586 B
ArmAsm
25 lines
586 B
ArmAsm
;
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; 2021-04-01, Greg King
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;
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; void waitvsync (void);
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; /* Wait for the start of the next video field. */
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;
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; VERA's vertical sync causes IRQs which increment the jiffy timer.
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;
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; Updated by ZeroByteOrg to use Kernal API RDTIM to retreive the TIMER variable
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;
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.export _waitvsync
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.proc _waitvsync: near
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RDTIM = $FFDE ; Kernal API for reading the jiffy timer
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jsr RDTIM
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sta lastjiffy
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keep_waiting:
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jsr RDTIM
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cmp #$FF ; self-mod the value returned by RDTIM to save memory
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lastjiffy=(*-1)
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beq keep_waiting
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rts
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.endproc
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