66 lines
1.4 KiB
ArmAsm
66 lines
1.4 KiB
ArmAsm
; Fuzzball -- a 29 byte Intro for Apple II
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; this one was an accident, it ends up walking through memory
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; a page at a time and using it as a shape table
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; by Deater / dSr
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; zero page locations
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HGR_SCALE = $E7
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; softswtich
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SPEAKER = $C030
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; ROM calls
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HGR2 = $F3D8
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HPOSN = $F411
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XDRAW0 = $F65D
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.zeropage
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; we load at address $E7 in memory, which is the location
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; of HGR_SCALE.
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; this is an artifact of the original program to get SCALE=$20
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; (from jsr opcode). But now we set SCALE=1 explicitly,
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; meaning we could in theory move the program
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; to load elsewhere
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tiny_tiny:
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jsr HGR2 ; Hi-res graphics, no text at bottom
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; Y=0, A=0 after this call
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iny ; #1
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sty HGR_SCALE
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tiny_loop:
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; move back to center of screen (screen is 280x192)
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ldy #0 ; upper byte always 0
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ldx #140 ; X-coord
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lda #96 ; Y-coord
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jsr HPOSN ; X-coord = (y,x) Y-coord =(a)
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bit SPEAKER ; click the speaker
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rot_smc:
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lda #0 ; ROT=0 (rotation value)
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tay ; ldy #>shape_table
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; The shape table is at memory address (Y,X)
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; The effect was found when the original code was modified to
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; have ROT not be 0, and so instead of pointing to the desired
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; shape table in the zero page it was walking all across memory
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; X is 140 here, since we are pointing at random data it doesn't
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; really matter what it is
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jsr XDRAW0 ; XDRAW 1 AT X-coord,Y-coord
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; Both A and X are 0 at exit
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inc rot_smc+1
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jmp tiny_loop ; use BVC to save byte?
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