mirror of
https://github.com/actraiser/dust-tutorial-c64-first-intro.git
synced 2025-06-19 09:25:38 -04:00
46 lines
1.9 KiB
NASM
46 lines
1.9 KiB
NASM
;============================================================
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; some initialization and interrupt redirect setup
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;============================================================
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sei ; set interrupt disable flag
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jsr init_screen ; clear the screen
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jsr init_text ; write lines of text
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jsr sid_init ; init music routine now
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ldy #$7f ; $7f = %01111111
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sty $dc0d ; Turn off CIAs Timer interrupts ($7f = %01111111)
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sty $dd0d ; Turn off CIAs Timer interrupts ($7f = %01111111)
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lda $dc0d ; by reading $dc0d and $dd0d we cancel all CIA-IRQs in queue/unprocessed
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lda $dd0d ; by reading $dc0d and $dd0d we cancel all CIA-IRQs in queue/unprocessed
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lda #$01 ; Set Interrupt Request Mask...
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sta $d01a ; ...we want IRQ by Rasterbeam (%00000001)
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lda $d011 ; Bit#0 of $d011 indicates if we have passed line 255 on the screen
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and #$7f ; it is basically the 9th Bit for $d012
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sta $d011 ; we need to make sure it is set to zero for our intro.
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lda #<irq ; point IRQ Vector to our custom irq routine
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ldx #>irq
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sta $314 ; store in $314/$315
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stx $315
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lda #$00 ; trigger first interrupt at row zero
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sta $d012
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cli ; clear interrupt disable flag
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jmp * ; infinite loop
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;============================================================
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; custom interrupt routine
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;============================================================
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irq dec $d019 ; acknowledge IRQ / clear register for next interrupt
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jsr colwash ; jump to color cycling routine
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jsr play_music ; jump to play music routine
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jmp $ea81 ; return to kernel interrupt routine |