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Pecusx
153 lines
2.9 KiB
NASM
153 lines
2.9 KiB
NASM
; --- dmsc LZSS player routine
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song_data
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ins 'mmm_16.lzs'
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song_end
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buffers
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.ds 256 * 9
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POKEY2 = POKEY+$10 ; stereo
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; Song Initialization - this runs in the first tick:
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;
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.proc init_song
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; pokeys init
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lda #3 ; stereo
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sta POKEY+$0f ; stereo
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sta POKEY2+$0f ; stereo
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mva #1 bit_data
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; Example: here initializes song pointer:
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;mwa #song_data song_ptr
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; Init all channels:
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ldx #8
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ldy #0
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clear
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; Read just init value and store into buffer and POKEY
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jsr get_byte
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sta POKEY, x
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sta POKEY2,x ; stereo
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sta stereo_buff,x ; stereo
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sty chn_copy, x
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cbuf
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sta buffers + 255
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inc cbuf + 2
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dex
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bpl clear
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; Initialize buffer pointer:
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sty bptr
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sty cur_pos
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rts
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.endp
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; Wait for next frame
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;
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.proc wait_frame
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lda 20
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delay
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cmp 20
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beq delay
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.endp
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; Play one frame of the song
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;
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.proc play_frame
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ldx #8 ; stereo
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@ lda stereo_buff,x ; stereo
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sta POKEY2,x ; stereo
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dex ;stereo
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bpl @- ; stereo
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lda #>buffers
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sta bptr+1
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lda song_data
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sta chn_bits
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ldx #8
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; Loop through all "channels", one for each POKEY register
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chn_loop:
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lsr chn_bits
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bcs skip_chn ; C=1 : skip this channel
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lda chn_copy, x ; Get status of this stream
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bne do_copy_byte ; If > 0 we are copying bytes
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; We are decoding a new match/literal
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lsr bit_data ; Get next bit
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bne got_bit
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jsr get_byte ; Not enough bits, refill!
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ror ; Extract a new bit and add a 1 at the high bit (from C set above)
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sta bit_data ;
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got_bit:
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jsr get_byte ; Always read a byte, it could mean "match size/offset" or "literal byte"
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bcs store ; Bit = 1 is "literal", bit = 0 is "match"
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sta chn_pos, x ; Store in "copy pos"
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jsr get_byte
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sta chn_copy, x ; Store in "copy length"
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; And start copying first byte
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do_copy_byte:
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dec chn_copy, x ; Decrease match length, increase match position
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inc chn_pos, x
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ldy chn_pos, x
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; Now, read old data, jump to data store
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lda (bptr), y
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store:
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ldy cur_pos
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sta POKEY,x ; Store to output and buffer
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sta stereo_buff,x ; stereo
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sta (bptr), y
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skip_chn:
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; Increment channel buffer pointer
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inc bptr+1
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dex
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bpl chn_loop ; Next channel
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inc cur_pos
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.endp
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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; Check for ending of song and jump to the next frame
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;
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; not checking really so the tune gets funky :)))
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;lda song_ptr + 1
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;cmp #>song_end
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;bne wait_frame
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;lda song_ptr
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;cmp #<song_end
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;bne wait_frame
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end_loop
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rts
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song_ptr = get_byte + 1
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.proc get_byte
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lda song_data+1
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inc song_ptr
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bne skip
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inc song_ptr+1
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skip
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rts
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.endp
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stereo_buff ; stereo
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.ds 9 ; stereo
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