91 lines
1.4 KiB
ArmAsm
91 lines
1.4 KiB
ArmAsm
SAVMSC = $58
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SDMCTL = $22F
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SDLSTL = $230
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SDLSTH = $231
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COLPF0 = $D016
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COLPF1 = $D017
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COLPF2 = $D018
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COLPF3 = $D019
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COLBK = $D01A
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WSYNC = $D40A
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VCOUNT = $D40B
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NMIEN = $D40E
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.data
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.import palette1
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.import palette2
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.import palette3
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.import framebuffer
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displaylist:
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.repeat 3
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.byte $70 ; 8 blank lines
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.endrep
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.byte $4e ; ANTIC mode e (160px 2bpp, 1 scan line per line)
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.addr framebuffer
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.repeat 191
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.byte $0e
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.endrep
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.byte $41 ; jump and blank
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.addr displaylist
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.code
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.export start
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; Loop through scan lines updating the palette
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.proc update_palette
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lda palette1,y
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pha
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ldx palette2,y
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lda palette3,y
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tay
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pla
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; Wait for horizontal blank
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sta WSYNC
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; Update color registers as fast as possible
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sta COLPF0
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stx COLPF1
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sty COLPF2
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rts
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.endproc
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.proc start
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; Disable display DMA
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lda #$00
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sta SDMCTL
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; Set up the display list
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lda #.lobyte(displaylist)
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sta SDLSTL
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lda #.hibyte(displaylist)
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sta SDLSTH
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; Turn off interrupts except reset button
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lda #$20
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sta NMIEN
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; Manually wait for first scan line
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wait_vblank:
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lda VCOUNT
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bne wait_vblank
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; Re-enable display DMA
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lda #$22
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sta SDMCTL
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even_scanline:
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ldy VCOUNT
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jsr update_palette
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odd_scanline:
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ldy VCOUNT
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iny
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jsr update_palette
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jmp even_scanline
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.endproc
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