120 lines
1.7 KiB
ArmAsm
120 lines
1.7 KiB
ArmAsm
;======================================
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; do very simple horizontal scroll
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;======================================
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; skips by 4 because we need fairly high FPS
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; originally ~12 seconds to scroll 80 (twice)
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; also assumes every-other line the same
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; screens to pan in $2000/$4000 to left
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horiz_pan_skip:
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pan_loop:
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; how many times to scroll
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lda #0
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sta COUNT
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pan_outer_outer_loop:
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ldx #191
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pan_outer_loop:
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txa
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pha
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; self-modify the PAGE1 high input addresses
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lda hposn_high,X
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sta pil_in_smc1+2 ; input source
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sta pil_out_smc1+2 ; output odd
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sta pil_out_smc4+2
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;self modify the PAGE2 high input addresses
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eor #$60
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sta pil_in_page2_smc1+2
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; self modify the PAGE1 LOW addresses
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lda hposn_low,X
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sta pil_out_smc1+1 ; output odd
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sta pil_out_smc4+1 ; output odd
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; self modify the PAGE1 LOW input addresses
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sta pil_in_smc1+1 ; input is regular+1
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inc pil_in_smc1+1
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; offset in PAGE2 to get input from
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clc
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adc COUNT
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sta pil_in_page2_smc1+1
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inx
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lda hposn_high,X
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sta pil_out_smc2+2 ; output even high
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sta pil_out_smc5+2
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lda hposn_low,X ; output even low
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sta pil_out_smc2+1
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sta pil_out_smc5+1
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;=========================
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; inner loop, from 0-39
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ldy #0
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pan_inner_loop:
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; load in+1, store to in
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; if completely unrolled, would save 1 cycle for store and
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; 5 for the branch/loop
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; 192*6=not a lot
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pil_in_smc1:
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lda $2000+1,Y ; 4
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pil_out_smc1:
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sta $2000,Y ; 5
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pil_out_smc2:
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sta $2000,Y ; 5
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iny ; 2
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cpy #39 ; 2
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bne pan_inner_loop ; 2/3
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; for right edge, scroll in from PAGE2
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pil_in_page2_smc1:
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lda $4000
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pil_out_smc4:
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sta $2000,Y
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pil_out_smc5:
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sta $2000,Y
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pla
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tax
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dex
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dex
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cpx #$ff
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bne pan_outer_loop
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inc COUNT
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lda COUNT
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cmp #39
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bne pan_outer_outer_loop
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rts
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