2021-12-11 02:50:10 +00:00
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;license:MIT
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;(c) 2017-2021 by qkumba/4am/John Brooks
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;
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!cpu 6502
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!to "build/DGR.FIZZLE",plain
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*=$6000
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2021-12-13 03:13:46 +00:00
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ldx #(end-start+1) ; copy LFSR code to zero page
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- ldy start-2, x
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sty $81, x
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2021-12-11 05:56:05 +00:00
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dex
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2021-12-12 19:05:36 +00:00
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bne -
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2021-12-11 05:56:05 +00:00
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2021-12-12 19:05:36 +00:00
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jmp loop
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2021-12-11 05:56:05 +00:00
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start
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2021-12-13 03:13:46 +00:00
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!pseudopc $83 {
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2021-12-11 05:56:05 +00:00
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;X=0
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;Y=0
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loop txa
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loop1 eor #$05 ; LFSR form 0x0500 with period 2047
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2021-12-13 03:13:46 +00:00
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wait inx
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bpl wait
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2021-12-11 05:56:05 +00:00
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tax
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loop2 tya
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2021-12-11 02:50:10 +00:00
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and #$78
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cmp #$78
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2021-12-11 05:56:05 +00:00
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beq next
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2021-12-12 21:56:51 +00:00
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txa
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ora #$04
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2021-12-12 19:05:36 +00:00
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sta <dst+2
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2021-12-13 03:13:46 +00:00
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txa
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;C=0
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adc #$7C
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bpl aux
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2021-12-11 02:50:10 +00:00
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sta $C004
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2021-12-13 03:13:46 +00:00
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!byte $24
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aux sta $C005
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setsrc sta <src+2
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2021-12-12 19:05:36 +00:00
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src lda $FD00, y ; SMC high byte
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dst sta $FD00, y ; SMC high byte
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2021-12-11 05:56:05 +00:00
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next txa
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lsr
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tax
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tya
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ror
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tay
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bcc loop2
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bne loop
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bit $C000
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bmi exit
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txa
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bne loop1
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2021-12-13 03:13:46 +00:00
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exit lda $7C00 ; last lousy byte (because LFSR never hits 0)
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!if *+1 != $C0 {
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!error *
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}
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2021-12-11 05:56:05 +00:00
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sta $0400
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sta $C004
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rts
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}
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end
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