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47 lines
841 B
ArmAsm
47 lines
841 B
ArmAsm
;================================
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; scrn routine
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;================================
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; Xcoord in XPOS
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; Ycoord in YPOS
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; color returned in A
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; assume reading from $c00
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scrn:
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lda YPOS ; 3
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and #$fe ; make even ; 2
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tay ; 2
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lda gr_offsets,Y ; lookup low-res memory address ; 4
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clc ; 2
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adc XPOS ; 3
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sta GBASL ; 3
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lda gr_offsets+1,Y ; 4
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adc #$8 ; assume reading from $c0 ; 3
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sta GBASH ; 3
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ldy #0 ; 2
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lda YPOS ; 3
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lsr ; 2
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bcs scrn_adjust_even ;2nt/3t
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scrn_adjust_odd:
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lda (GBASL),Y ; top/bottom color ; 5+
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jmp scrn_done ; 3
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scrn_adjust_even:
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lda (GBASL),Y ; top/bottom color ; 5+
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lsr ; 2
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lsr ; 2
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lsr ; 2
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lsr ; 2
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scrn_done:
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and #$f ; 2
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rts ; 6
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