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86 lines
1.6 KiB
Plaintext
86 lines
1.6 KiB
Plaintext
;license:MIT
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;(c) 2017-2018 by qkumba
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;
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; NOTE: must be run from language card, or caller must ensure that
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; this code is in an identical location in auxmem
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;
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FizzleDHGR
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;init RNG
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ldx #1
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stx @rnd1+1
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dex
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stx @rnd2+1
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;iterate
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@loop
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ldy @rnd1+1
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ldx @rnd2+1
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lsr @rnd2+1
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ror @rnd1+1
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bcc +
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;feedback polynomial forms #$2015 for period of 16383
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lda @rnd1+1
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eor #$15
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sta @rnd1+1
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lda @rnd2+1
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eor #$20
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sta @rnd2+1
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;little hack to avoid missing offset zero
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;screen hole at $xxFF is missed instead
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+ tya
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eor #$ff
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sta $26
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sta $3c
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txa
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and #$1f
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;target page 1
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ora #$20
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sta $27
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eor #$60
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sta $3d
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;copy pixel from other page to this page
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ldy #0
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cpx #$20
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bcc +
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sta $c003
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sta $c005
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+ lda ($3c),y
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sta ($26),y
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sta $c002
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sta $c004
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;check for keypress
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lda $c000
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bmi @exit
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;and exit condition
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@rnd2 lda #0
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bne @loop
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@rnd1 lda #0
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cmp #1
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bne @loop
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;graphics mode
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sta $c00d
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sta $c057
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sta $c054
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sta $c052
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sta $c050
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sta $c05e
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@exit
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rts
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