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165 lines
3.4 KiB
ArmAsm
165 lines
3.4 KiB
ArmAsm
;
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; Christian Groessler, June 2004
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;
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; void __fastcall__ _scroll (signed char numlines);
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; numlines > 0 scrolls up
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; numlines < 0 scrolls down
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;
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.include "atari.inc"
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.importzp tmp1,tmp4,ptr1,ptr2
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.import mul40,_clrscr
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.export __scroll
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.proc __scroll
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cmp #0
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beq jmpfin
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; cmp #$80
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; bcc up
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bpl up
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;scroll down
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eor #$ff
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clc
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adc #1 ; make positive
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sta tmp1
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cmp #24 ; scroll >= the whole screen?
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bcc down_ok
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jmp _clrscr
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down_ok:lda SAVMSC
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clc
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adc #<(40*23)
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sta ptr1
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sta ptr2
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lda SAVMSC+1
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adc #>(40*23)
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sta ptr1+1 ; point to last line on screen
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sta ptr2+1
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lda tmp1
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jsr mul40
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sta tmp4
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lda ptr2
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sec
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sbc tmp4
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sta ptr2
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stx tmp4
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lda ptr2+1
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sbc tmp4
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sta ptr2+1
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lda #24 ; # of lines on screen
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sec
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sbc tmp1 ; # of lines to move
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tax
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;very simple, could be improved
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scrold: ldy #39 ; # of chars on a line - 1
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copy_d: lda (ptr2),y
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sta (ptr1),y
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dey
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bpl copy_d
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lda ptr1
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sec
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sbc #40
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sta ptr1
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bcs u1
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dec ptr1+1
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u1: lda ptr2
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sec
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sbc #40
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sta ptr2
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bcs u2
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dec ptr2+1
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u2: dex
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bne scrold
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; fill new scrolled in lines with space
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ldx tmp1 ; # of new lines
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fild: lda #0
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ldy #39
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fill_d: sta (ptr1),y
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dey
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bpl fill_d
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dex
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jmpfin: beq finish
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lda ptr1
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sec
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sbc #40
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sta ptr1
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bcs u3
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dec ptr1+1
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u3: jmp fild
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;scroll up
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up: sta tmp1 ; # of lines to scroll
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cmp #24 ; scroll >= the whole screen?
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bcc up_ok
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jmp _clrscr
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;multiply by 40 (xsize)
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up_ok: jsr mul40
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clc
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adc SAVMSC ; add start of screen mem
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sta ptr2
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txa
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adc SAVMSC+1
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sta ptr2+1
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lda SAVMSC+1
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sta ptr1+1
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lda SAVMSC
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sta ptr1
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lda #24 ; # of lines on screen
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sec
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sbc tmp1 ; # of lines to move
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tax
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;very simple, could be improved
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scroll: ldy #39 ; # of chars on a line - 1
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copy_l: lda (ptr2),y
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sta (ptr1),y
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dey
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bpl copy_l
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lda #40
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clc
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adc ptr1
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sta ptr1
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bcc l1
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inc ptr1+1
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l1: lda #40
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clc
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adc ptr2
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sta ptr2
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bcc l2
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inc ptr2+1
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l2: dex
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bne scroll
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; fill new scrolled in lines with space
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ldx tmp1 ; # of new lines
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fill: lda #0
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ldy #39
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fill_l: sta (ptr1),y
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dey
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bpl fill_l
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dex
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beq finish
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lda #40
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clc
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adc ptr1
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sta ptr1
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bcc l3
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inc ptr1+1
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l3: jmp fill
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finish: rts
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.endproc
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