dither4/dither4.s

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SAVMSC = $58
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COLPF0 = $D016
COLPF1 = $D017
COLPF2 = $D018
COLPF3 = $D019
COLBK = $D01A
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AUDC1 = $D201
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DMACTL = $D400
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DLISTL = $D402
DLISTH = $D403
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WSYNC = $D40A
VCOUNT = $D40B
NMIEN = $D40E
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framebuffer = $a000
framebuffer2 = $b000
temp1l = $80
temp1h = $81
temp1 = temp1l
temp2l = $82
temp2h = $83
temp2 = temp2l
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sample_ptrl = $84
sample_ptrh = $85
sample_ptr = sample_ptrl
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scanline = $86
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audiotemp = $87
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height = 160
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bytes_per_line = 40
pages_per_frame = 32
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lines_per_frame = 262
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;scanline_offset = 31 + (40 - 24) / 2
scanline_offset = 47
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scanline_max = (lines_per_frame - scanline_offset) / 2
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.data
.import palette1
.import palette2
.import palette3
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.import bitmap
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.import audio_samples
.import audio_samples_end
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displaylist:
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; 40 lines overscan
.repeat 5
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.byte $70 ; 8 blank lines
.endrep
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; 160 lines graphics
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; ANTIC mode e (160px 2bpp, 1 scan line per line)
.byte $4e
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.addr framebuffer
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.repeat height / 2 - 1
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.byte $0e
.endrep
.byte $4e
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.addr framebuffer2
.repeat height / 2 - 1
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.byte $0e
.endrep
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.byte $41 ; jump and blank
.addr displaylist
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audio_high_byte:
.scope
.macro byteseq val
.repeat 16
.byte val | $10
.endrep
.endmacro
byteseq $0
byteseq $1
byteseq $2
byteseq $3
byteseq $4
byteseq $5
byteseq $7
byteseq $8
byteseq $9
byteseq $a
byteseq $b
byteseq $c
byteseq $d
byteseq $e
byteseq $f
.endscope
.code
.export start
.proc start
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; Copy the bitmap into our framebuffer
lda #.lobyte(bitmap)
sta temp1l
lda #.hibyte(bitmap)
sta temp1h
lda #.lobyte(framebuffer)
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sta temp2l
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lda #.hibyte(framebuffer)
sta temp2h
jsr copy_half_frame
; Second half of bitmap has to be separately aligned
lda #.lobyte(framebuffer2)
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sta temp2l
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lda #.hibyte(framebuffer2)
sta temp2h
jsr copy_half_frame
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; Set up the audio sample buffer
lda #.lobyte(audio_samples)
sta sample_ptrl
lda #.hibyte(audio_samples)
sta sample_ptrh
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; Disable display DMA
lda #$00
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sta DMACTL
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; Disable VBI and DLI but allow Reset
lda #32
sta NMIEN
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; Set up the display list
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lda #.lobyte(displaylist)
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sta DLISTL
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lda #.hibyte(displaylist)
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sta DLISTH
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; Manually wait for first scan line
wait_vblank:
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sta WSYNC
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lda VCOUNT
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bne wait_vblank
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; Re-enable display DMA
lda #$22
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sta DMACTL
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wait_start:
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; Wait for the vblank
; Resynchronize the scanline counter
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wait_loop:
lda VCOUNT
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tay ; save for audio lookup
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bne wait_loop
lda #(256 - scanline_offset)
sta scanline
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each_scanline:
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.macro audio_prep
ldy VCOUNT ; 4 cycles
lda (sample_ptr),y ; 5/6 cyc
sta audiotemp ; 3 cyc
.endmacro
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.macro inner_scanline
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; it'll fire on unused lines, but harmlessly
ldy scanline ; 3 cyc
inc scanline ; 5 cyc
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; Leisurely memory fetches
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lda palette1,y ; 5
pha ; ...3?
ldx palette2,y ; 5
lda palette3,y ; 5
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tay
pla
; Wait for horizontal blank
sta WSYNC
; Update color registers as fast as possible
sta COLPF0
stx COLPF1
sty COLPF2
.endmacro
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.macro audio_play_lo ; 11 cycles
lda audiotemp ; 3 cyc
and #$0f ; 2 cyc
ora #$10 ; 2 cyc
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sta AUDC1 ; 4 cyc
.endmacro
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.macro audio_play_hi ; 12 cycles
ldy audiotemp ; 3 cyc
lda audio_high_byte,y ; 5 cyc
sta AUDC1 ; 4 cyc
.endmacro
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.macro audio_inc
; Increment sample ptr
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clc
lda sample_ptrl
adc #130
sta sample_ptrl
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lda sample_ptrh
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adc #0
sta sample_ptrh
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cmp #.hibyte(audio_samples_end)
bne audio_cont
;lda sample_ptrl
;cmp #.lobyte(audio_samples_end)
;bne audio_cont
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lda #.lobyte(audio_samples)
sta sample_ptrl
lda #.hibyte(audio_samples)
sta sample_ptrh
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audio_cont:
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.endmacro
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audio_prep
inner_scanline
audio_play_lo
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inner_scanline
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audio_play_hi
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lda VCOUNT
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cmp #130 ;#130
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bne each_scanline
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audio_inc
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jmp wait_start
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.endproc
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; temp1 contains source address
; temp2 contains dest address
; clobbers a/x/y
; incremepts temp1 and temp2 to the end of their regions
.proc copy_half_frame
ldx #0
copy_loop_lines:
ldy #00
copy_loop_bytes:
lda (temp1),y
sta (temp2),y
iny
cpy #bytes_per_line
bne copy_loop_bytes
clc
lda temp1l
adc #bytes_per_line
sta temp1l
lda temp1h
adc #00
sta temp1h
clc
lda temp2l
adc #bytes_per_line
sta temp2l
lda temp2h
adc #00
sta temp2h
inx
cpx #(height / 2)
bne copy_loop_lines
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rts
.endproc