Working Python version for Commodore.

c64view/viewer/fli.s

@@ -0,0 +1,151 @@
+; c64view -- FLI multicolor viewer (self-contained)
+;
+; Re-points the VIC video matrix ($D018) and forces a badline ($D011 yscroll)
+; on every visible raster line via a cycle-timed loop, giving per-line colour.
+;
+; Memory layout of appended data (loads from $4000):
+;   $4000+L*$400  screen RAM for line L (L=0..7), 1000 bytes each
+;   $6000         bitmap 8000   (offset $2000 in VIC bank 1)
+;   $8000         colour RAM 1000  (copied to $D800)
+;   $83E8         background 1
+;
+; assembled by viewer/assemble.py via xa
+
+        ; BASIC autostart, SYS 2061
+        * = $0801
+        .word basicend
+        .word 10
+        .byte $9e
+        .byte "2061"
+        .byte 0
+basicend:
+        .word 0                   ; ML begins at $080D
+
+start:
+        sei
+
+        ; copy colour RAM $8000 -> $D800 (1024 bytes)
+        ldx #0
+ccopy:
+        lda $8000,x
+        sta $d800,x
+        lda $8100,x
+        sta $d900,x
+        lda $8200,x
+        sta $da00,x
+        lda $8300,x
+        sta $db00,x
+        inx
+        bne ccopy
+
+        ; build per-line tables. d018tab = ((line AND 7) << 4) OR $08
+        ; d011tab = $38 OR (line AND 7)   = BMM+DEN+RSEL plus yscroll
+        ldx #0
+btab:
+        txa
+        and #$07
+        asl
+        asl
+        asl
+        asl
+        ora #$08
+        sta d018tab,x
+        ; yscroll must equal (raster AND 7) to force a badline; the first
+        ; displayed raster is 51, so line x maps to raster 51+x.
+        txa
+        clc
+        adc #$03
+        and #$07
+        ora #$38
+        sta d011tab,x
+        inx
+        bne btab
+
+        ; VIC bank 1 ($4000-$7FFF)
+        lda $dd00
+        and #$fc
+        ora #$02
+        sta $dd00
+
+        lda $83e8
+        sta $d021                 ; background
+        lda #$00
+        sta $d020                 ; border black
+        lda #$d8
+        sta $d016                 ; multicolor on
+
+        ; raster IRQ setup
+        lda #<irq1
+        sta $0314
+        lda #>irq1
+        sta $0315
+        lda #$7f
+        sta $dc0d                 ; disable CIA timer IRQs
+        sta $dd0d
+        lda $dc0d
+        lda $dd0d
+        lda #$01
+        sta $d01a                 ; enable raster IRQ
+        lda #$30
+        sta $d012                 ; line 48
+        lda $d011
+        and #$7f
+        sta $d011
+        asl $d019                 ; ack
+        cli
+hang:
+        jmp hang
+
+; first IRQ, arrives with jitter on line 48, sets up the stabilised one
+irq1:
+        lda #<irq2
+        sta $0314
+        lda #>irq2
+        sta $0315
+        inc $d012                 ; fire again next line (49)
+        asl $d019                 ; ack
+        tsx
+        cli
+        ; burn the rest of the line so irq2 fires inside this NOP slide
+        .dsb 40,$ea               ; 40 NOPs
+
+; stabilised IRQ on line 49, runs the FLI loop
+irq2:
+        txs                       ; restore sp from irq1
+        ; cancel the remaining 0/1-cycle jitter: read the raster twice; the
+        ; branch is 2 or 3 cycles depending on alignment, normalising entry.
+        lda $d012
+        cmp $d012
+        beq jl
+jl:
+        ; fixed delay so the first store lands before the c-access window
+        ldx #$0d
+d0:     dex
+        bne d0
+        nop
+        nop
+
+        ldx #$00
+fliloop:
+        lda d011tab,x             ; force badline (yscroll = line&7)
+        sta $d011
+        lda d018tab,x             ; point video matrix at screen[line]
+        sta $d018
+        inx
+        cpx #200
+        bne fliloop
+
+        ; bottom border: leave bitmap on but stop forcing badlines
+        lda #<irq1
+        sta $0314
+        lda #>irq1
+        sta $0315
+        lda #$30
+        sta $d012
+        asl $d019
+        jmp $ea81                 ; restore regs + RTI
+
+d018tab:
+        .dsb 256,0
+d011tab:
+        .dsb 256,0