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shave some cycles (use 80STORE mode for 1-STA bank switching) [thanks John B.]

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4am 2020-11-22 21:12:40 -05:00
parent fd4cd16936
commit a3dc564852
1 changed files with 6 additions and 6 deletions
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12
src/fx/fx.dhgr.2bit.fizzle.a
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@ -50,8 +50,7 @@ copymasks = $6200 ; [256 bytes, page-aligned, duplicated in a
start start
!pseudopc 0 { !pseudopc 0 {
!byte %00000011 !byte %00000011
copyaux sta $C003 copyaux sta $C003 ; copy $4000/aux to $A000/main
sta $C005
ldx #$20 ldx #$20
ldy #$00 ldy #$00
a lda $4000, y a lda $4000, y
@ -62,14 +61,15 @@ b sta $A000, y
inc b+2 inc b+2
dex dex
bne a bne a
sta $C002
sta $C001 ; 80STORE mode
; X,Y=0 on entry to LFSR ; X,Y=0 on entry to LFSR
loop txa loop txa
loop1 eor #$B4 ; LFSR form 0xB400 with period 65535 loop1 eor #$B4 ; LFSR form 0xB400 with period 65535
tax ; X is LFSR high byte, Y is LFSR low byte tax ; X is LFSR high byte, Y is LFSR low byte
loop2 lda addrs, x ; which means X is the index into the base address lookup table loop2 lda addrs, x ; which means X is the index into the base address lookup table
bmi aux ; and Y is the offset from the base address bmi aux ; and Y is the offset from the base address
sta $C002 sta $C054 ; switch $2000 access to main memory
sta $C004
sta <dst+2 sta <dst+2
eor #$60 eor #$60
sta <src+2 sta <src+2
@ -92,10 +92,10 @@ dst sta $FD00, y ; write the result
bne loop1 bne loop1
exit lda $4000 ; last lousy byte (because LFSR never hits 0) exit lda $4000 ; last lousy byte (because LFSR never hits 0)
sta $2000 sta $2000
sta $C000 ; 80STORE mode off
rts rts
aux sta $C003 aux sta $C055 ; switch $2000 access to aux memory (read/write!)
sta $C005
sta <auxsrc+2 sta <auxsrc+2
eor #$80 eor #$80
sta <auxdst+2 sta <auxdst+2