68 lines
1.1 KiB
ArmAsm
68 lines
1.1 KiB
ArmAsm
scroll_row1 = $800
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scroll_row2 = $900
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scroll_row3 = $A00
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scroll_row4 = $B00
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SCROLL_LENGTH = $63
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;OFFSET = $62
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; 5 + (45*40) +4 + 13 + 7 + 6 = 1835
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scroll_loop:
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ldx #0 ; 2
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ldy OFFSET ; 3
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draw_loop:
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lda scroll_row1,Y ; 4
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sta $650,X ; 5
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lda scroll_row2,Y ; 4
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sta $6d0,X ; 5
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lda scroll_row3,Y ; 4
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sta $750,X ; 5
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lda scroll_row4,Y ; 4
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sta $7d0,X ; 5
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iny ; 2
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inx ; 2
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cpx #40 ; 2
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bne draw_loop ; 2nt/3
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;===============
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; 45
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; -1
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inc OFFSET ; 5
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;============
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; 4
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;==================
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; wrap scrolltext
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;==================
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clc ; 2
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lda OFFSET ; 3
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adc #40 ; 2
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cmp SCROLL_LENGTH ; 3
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bne no_wrap ; 3
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;============
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; 13
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; -1
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lda #0 ; 2
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sta OFFSET ; 3
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jmp done_wrap ; 3
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no_wrap:
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lda $0 ; 3
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nop ; 2
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nop ; 2
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;===========
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; 7
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done_wrap:
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rts ; 6
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.assert >scroll_loop = >done_wrap, error, "gr_scroll crosses page"
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