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58 lines
1.2 KiB
Plaintext
58 lines
1.2 KiB
Plaintext
;license:MIT
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;(c) 2019-2020 by qkumba/4am/John Brooks
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!cpu 6502
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!to "build/FX.INDEXED/SHR.FIZZLE",plain
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*=$A000
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!source "src/fx/macros.a"
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addrs=$7F ; [128 bytes]
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lda #$A0 ; create address lookup table
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tax
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tay
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- dey
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sty addrs-$21, x
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dex
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bne -
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+OVERCOPY_TO_0 start, end
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;$FF clobbered
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;X=0
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;Y=0
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+COPY_SCB_AND_PALETTES
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;WRITEAUXMEM active
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jmp loop
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start
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!pseudopc 0 {
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;X=0
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;Y=0
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loop txa
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loop1 eor #$60 ; LFSR form 0x6000 with period 32767
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tax
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loop2 lda addrs, x
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sta <src+2
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src lda $FD00, y ; SMC high byte
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sta (src+1), y
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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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lda (src+1), y ; last lousy byte (because LFSR never hits 0)
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sta (src+1), y
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exit rts
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}
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end
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