102 lines
1.7 KiB
ArmAsm
102 lines
1.7 KiB
ArmAsm
;================================
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; HGR vscroll
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;================================
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; image to scroll in is in $A000
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;
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; At SCROLL=96 timing = 44,543 + 66,629 = 111,172 cycles
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; = approx 9 frames/second so 21s to scroll screen
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hgr_vscroll:
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ldx #191 ; 2
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stx SCROLL ; SCROLL = 0 ; 3
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vscroll_loop:
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; for x=0 to SCROLL
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; write 40 bytes of 00
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ldx #0 ; 2
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vscroll_inner:
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lda hposn_high,X ; 4
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sta OUTH ; 3
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lda hposn_low,X ; 4
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sta OUTL ; 3
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;====
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; 14
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ldy #39 ; 2
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lda #0 ; 2
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;===
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; 4
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vscroll_line:
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sta (OUTL),Y ; 6
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dey ; 2
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bpl vscroll_line ; 2/3
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;=====
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; 4+(40*11)-1
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; 443
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inx ; 2
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cpx SCROLL ; 2
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bne vscroll_inner ; 2/3
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;===============
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; assume SCROLL=96
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; 96*(14+443+7)-1
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;
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;====================
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; draw bottom part
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lda #0 ; 2
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sta SCROLL_OFFSET ; 3
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vscroll_bottom:
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stx XSAVE ; 3
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ldx SCROLL_OFFSET ; 3
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lda hposn_high,X ; 4
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clc ; 2
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adc #$80 ; ora instead? ; 2
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sta INH ; 3
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lda hposn_low,X ; 4
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sta INL ; 3
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;====
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; 24
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inc SCROLL_OFFSET ; 5
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ldx XSAVE ; 3
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lda hposn_high,X ; 4
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sta OUTH ; 3
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lda hposn_low,X ; 4
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sta OUTL ; 3
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;====
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; 22
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ldy #39 ; 2
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vscroll_bottom_line:
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lda (INL),Y ; 5
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sta (OUTL),Y ; 6
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dey ; 2
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bpl vscroll_bottom_line ; 2/3
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;=====
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; 2+40*(16)-1
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; 641
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inx ; 2
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cpx #192 ; 2
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bne vscroll_bottom ; 2/3
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;==========
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;5+96*(46+641+7)-1
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; 66629
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;=====================
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; scroll whole screen
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dec SCROLL
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bne vscroll_loop
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rts
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