dither4/dither4.s

256 lines
4.3 KiB
ArmAsm

SAVMSC = $58
COLPF0 = $D016
COLPF1 = $D017
COLPF2 = $D018
COLPF3 = $D019
COLBK = $D01A
AUDC1 = $D201
DMACTL = $D400
DLISTL = $D402
DLISTH = $D403
WSYNC = $D40A
VCOUNT = $D40B
NMIEN = $D40E
framebuffer = $a000
framebuffer2 = $b000
temp1l = $80
temp1h = $81
temp1 = temp1l
temp2l = $82
temp2h = $83
temp2 = temp2l
sample_ptrl = $84
sample_ptrh = $85
sample_ptr = sample_ptrl
height = 192
bytes_per_line = 40
pages_per_frame = 32
lines_per_frame = 262
.data
.import palette1
.import palette2
.import palette3
.import bitmap
.import audio_samples
.import audio_samples_end
displaylist:
; 24 lines overscan
.repeat 3
.byte $70 ; 8 blank lines
.endrep
; 192 lines graphics
; ANTIC mode e (160px 2bpp, 1 scan line per line)
.byte $4e
.addr framebuffer
.repeat height / 2 - 1
.byte $0e
.endrep
.byte $4e
.addr framebuffer2
.repeat height / 2 - 1
.byte $0e
.endrep
.byte $41 ; jump and blank
.addr displaylist
.code
.export start
.proc start
; Copy the bitmap into our framebuffer
lda #.lobyte(bitmap)
sta temp1l
lda #.hibyte(bitmap)
sta temp1h
lda #.lobyte(framebuffer)
sta temp2l
lda #.hibyte(framebuffer)
sta temp2h
jsr copy_half_frame
; Second half of bitmap has to be separately aligned
lda #.lobyte(framebuffer2)
sta temp2l
lda #.hibyte(framebuffer2)
sta temp2h
jsr copy_half_frame
; Set up the audio sample buffer
lda #.lobyte(audio_samples)
sta sample_ptrl
lda #.hibyte(audio_samples)
sta sample_ptrh
; Disable display DMA
lda #$00
sta DMACTL
; Disable VBI and DLI but allow Reset
lda #32
sta NMIEN
; Set up the display list
lda #.lobyte(displaylist)
sta DLISTL
lda #.hibyte(displaylist)
sta DLISTH
; Manually wait for first scan line
wait_vblank:
;sta WSYNC
lda VCOUNT
bne wait_vblank
; Re-enable display DMA
lda #$22
sta DMACTL
; Wait for the next even scanline (VCOUNT is scan line / 2, so look for a change)
wait_start:
lda VCOUNT
sta temp1
wait_loop:
lda VCOUNT
cmp temp1
beq wait_loop
each_scanline:
lda VCOUNT
; Resynchronize the scanline counter
; it'll fire on unused lines, but harmlessly
clc
sbc #15
asl
tay
.macro audio_prep
; audio sample; low nybble
ldx #0
lda (sample_ptr,x)
sta temp2
; high nybble
lsr a
lsr a
lsr a
lsr a
; set the volume-only bit
ora #$10
pha
; low nybble
lda temp2
and #$0f
; set the volume-only bit
ora #$10
pha
.endmacro
.macro audio_inc
; Increment sample ptr
clc
lda sample_ptrl
adc #1
sta sample_ptrl
lda sample_ptrh
adc #0
sta sample_ptrh
lda sample_ptrh
cmp #.hibyte(audio_samples_end)
bne audio_cont
lda sample_ptrl
cmp #.lobyte(audio_samples_end)
bne audio_cont
lda #.lobyte(audio_samples)
sta sample_ptrl
lda #.hibyte(audio_samples)
sta sample_ptrh
audio_cont:
.endmacro
.macro inner_scanline
; Leisurely memory fetches
lda palette1,y
pha
ldx palette2,y
lda palette3,y
tay
pla
; Wait for horizontal blank
sta WSYNC
; Update color registers as fast as possible
sta COLPF0
stx COLPF1
sty COLPF2
; Audio sample
pla
sta AUDC1
.endmacro
audio_prep
inner_scanline
audio_inc
iny
inner_scanline
;jmp wait_start
jmp each_scanline
.endproc
; 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
rts
.endproc