2014-05-12 01:02:17 +00:00
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;
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; IRQ handling (ATARI 5200 version)
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;
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.export initirq, doneirq
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.import callirq
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.include "atari5200.inc"
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2014-05-26 23:47:37 +00:00
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; ------------------------------------------------------------------------
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2016-03-06 20:26:22 +00:00
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.segment "ONCE"
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2014-05-12 01:02:17 +00:00
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initirq:
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2014-05-26 23:47:37 +00:00
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lda VVBLKD
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ldx VVBLKD+1
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sta IRQInd+1
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stx IRQInd+2
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ldy #<IRQStub
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ldx #>IRQStub
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jmp SETVBV
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; ------------------------------------------------------------------------
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.code
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2014-05-12 01:02:17 +00:00
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doneirq:
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2014-05-26 23:47:37 +00:00
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ldy IRQInd+1
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ldx IRQInd+2
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;jmp SETVBV
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; fall thru
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; ------------------------------------------------------------------------
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; Set deferred vertical blank interrupt
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; logic copied from Atari computer ROM
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SETVBV: txa
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ldx #5
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sta WSYNC ; waste 20 CPU cycles
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@1: dex ; to allow VBLANK to happen
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bne @1 ; if this is line "7C"
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sta VVBLKD+1
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sty VVBLKD
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2014-05-12 01:02:17 +00:00
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rts
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2014-05-26 23:47:37 +00:00
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; ------------------------------------------------------------------------
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.segment "LOWCODE"
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IRQStub:
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cld ; Just to be sure
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jsr callirq ; Call the functions
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jmp IRQInd ; Jump to the saved IRQ vector
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; ------------------------------------------------------------------------
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.data
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IRQInd: jmp $0000
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