121 lines
1.4 KiB
ArmAsm
121 lines
1.4 KiB
ArmAsm
GBASL = $26
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GBASH = $27
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HGRPAGE = $E6
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PAGE0 = $C054
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PAGE1 = $C055
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HGR = $F3E2
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HGR2 = $F3D8
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HCLR = $F3F2
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HPOSN = $F411
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WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us
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snow:
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jsr HGR
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jsr HGR2
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lda #0
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sta ybase
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lda #$20
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sta HGRPAGE
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move_snow:
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lda HGRPAGE
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cmp #$20
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beq show_page1
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show_page2:
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bit PAGE1
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lsr HGRPAGE
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bne doit
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show_page1:
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bit PAGE0
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asl HGRPAGE
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doit:
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jsr HCLR
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lda #<flake
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sta ll_smc+1
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lda #$18
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sta c_smc
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lda #$69
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sta dir_smc
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lda #23
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sta line
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inc ybase
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lda ybase
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sta ylo
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cmp #160
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bne snow_loop
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lda #0
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sta ybase
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snow_loop:
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ldy xhi
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ldx xlo
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lda ylo
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jsr HPOSN
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ldx #0
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line_loop:
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ll_smc:
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lda flake,X
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sta (GBASL),Y
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inx
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iny
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cpx #6
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bne line_loop
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lda ll_smc+1
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c_smc:
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clc
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dir_smc:
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adc #6
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sta ll_smc+1
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inc ylo
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dec line
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beq forever
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lda line
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cmp #12
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bne snow_loop
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lda #$E9 ; sbc imm
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sta dir_smc
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lda #$38 ; sec
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sta c_smc
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jmp snow_loop
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forever:
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jmp move_snow
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xhi: .byte $00
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xlo: .byte 77
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ybase: .byte 100
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ylo: .byte 100
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line: .byte 23
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flake:
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.byte $00,$00,$40,$01,$00,$00
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.byte $00,$00,$0C,$18,$00,$00
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.byte $00,$00,$70,$07,$00,$00
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.byte $00,$00,$43,$61,$00,$00
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.byte $00,$00,$4C,$19,$00,$00
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.byte $33,$00,$70,$07,$00,$66
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.byte $30,$06,$40,$01,$30,$06
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.byte $3f,$06,$40,$01,$30,$7e
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.byte $40,$07,$30,$06,$70,$01
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.byte $7c,$07,$30,$06,$70,$1f
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.byte $00,$18,$0F,$78,$0C,$00
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.byte $00,$60,$40,$01,$03,$00
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