; lenser -- Atari GR.15 + DLI slideshow viewer (per-line colour).
;
; Self-booting (OS loads this to $2000, JSRs $2006).  Steps through NIMAGES
; pictures stored as raw sectors -- image i at sectors BASESEC + i*SPI -- SIO-
; reading SPI sectors into $4000 (bitmap $4000/$5000, colour table $6000 of
; 96 bands x 4, display list $6400) and showing each with a display-list
; interrupt that rewrites the four colour registers every two scanlines.
;
; build-time #defines -- WAITMODE WAITSECS RATE NIMAGES LOOPFLAG BASESEC SPI.

CP = $cb                        ; zero-page pointer into the colour table

        * = $2000
boot:
        .byte 0                 ; flags
        .byte 0                 ; sector count (patched)
        .word $2000
        .word binit

cont:                           ; $2006 -- OS JSRs here after loading the stub
        sei
        lda #$00
        sta $26f                ; GPRIOR = 0
        lda #$00
        sta $230                ; SDLSTL = $6400 (the loaded display list)
        lda #$64
        sta $231
        lda #<dli
        sta $200
        lda #>dli
        sta $201
        ldy #<vbi
        ldx #>vbi
        lda #$07
        jsr $e45c               ; SETVBV (deferred VBI)
        lda #$00
        sta ssidx
        cli

ssmain:
        lda #$00
        sta $d40e               ; NMIEN off (no DLI/VBI while loading)
        sta $22f                ; SDMCTL off (blank)
        jsr readimg             ; SIO-load image ssidx (IRQ stays on for SIOV)
        ; re-init the colour pointer + band-0 colours for the new image
        lda #$04
        sta CP
        lda #$60
        sta CP+1
        lda $6000
        sta $2c8
        lda $6001
        sta $2c4
        lda $6002
        sta $2c5
        lda $6003
        sta $2c6
        lda #$c0
        sta $d40e               ; NMIEN = DLI + VBI
        lda #$22
        sta $22f                ; SDMCTL = playfield + DL DMA
        jsr sswait
        inc ssidx
        lda ssidx
        cmp #NIMAGES
        bcc ssmain
#if LOOPFLAG == 1
        lda #$00
        sta ssidx
        jmp ssmain
#else
        sei
        lda #$00
        sta $d40e               ; NMIEN off
        lda #$40
        sta $d40e               ; restore VBI only (OS housekeeping)
        lda #$00
        sta $09
        cli
        jmp $e474               ; warm-start (exit)
#endif

binit:
        rts

; ---- SIO read SPI sectors of image ssidx into $4000 ----
readimg:
        lda #<BASESEC
        sta secn
        lda #>BASESEC
        sta secn+1
        ldx ssidx
        beq rsbuf
radd:
        clc
        lda secn
        adc #SPI
        sta secn
        bcc ra1
        inc secn+1
ra1:
        dex
        bne radd
rsbuf:
        lda #$00
        sta $0304
        lda #$40
        sta $0305
        lda #SPI
        sta cnt
rloop:
        lda #$31
        sta $0300
        lda #$01
        sta $0301
        lda #$52
        sta $0302
        lda #$40
        sta $0303
        lda #$1f
        sta $0306
        lda #$80
        sta $0308
        lda #$00
        sta $0309
        lda secn
        sta $030a
        lda secn+1
        sta $030b
        jsr $e459               ; SIOV
        clc
        lda $0304
        adc #$80
        sta $0304
        bcc rb1
        inc $0305
rb1:
        inc secn
        bne rb2
        inc secn+1
rb2:
        dec cnt
        bne rloop
        rts

; ---- wait (returns; defeats attract mode via $4d) ----
sswait:
#if WAITMODE == 1
        lda #$ff
        sta $2fc
sw1:
        lda #$00
        sta $4d
        lda $2fc
        cmp #$ff
        beq sw1
        rts
#endif
#if WAITMODE == 2
        lda #$00
        sta $12
        sta $13
        sta $14
sw2:
        lda #$00
        sta $4d
        lda $13
        cmp #>(WAITSECS*RATE)
        bcc sw2
        bne sw2d
        lda $14
        cmp #<(WAITSECS*RATE)
        bcc sw2
sw2d:
        rts
#endif
#if WAITMODE == 3
        lda #$ff
        sta $2fc
        lda #$00
        sta $12
        sta $13
        sta $14
sw3:
        lda #$00
        sta $4d
        lda $2fc
        cmp #$ff
        bne sw3d
        lda $13
        cmp #>(WAITSECS*RATE)
        bcc sw3
        bne sw3d
        lda $14
        cmp #<(WAITSECS*RATE)
        bcc sw3
sw3d:
        rts
#endif

ssidx:  .byte 0
secn:   .word 0
cnt:    .byte 0

; reset colour pointer + band-0 colours each frame (from the loaded $6000 table)
vbi:
        lda #$04
        sta CP
        lda #$60
        sta CP+1
        lda $6000
        sta $d01a
        lda $6001
        sta $d016
        lda $6002
        sta $d017
        lda $6003
        sta $d018
        jmp $e462               ; XITVBV

dli:
        pha
        tya
        pha
        ldy #$00
        sta $d40a               ; WSYNC
        lda (CP),y
        sta $d01a
        iny
        lda (CP),y
        sta $d016
        iny
        lda (CP),y
        sta $d017
        iny
        lda (CP),y
        sta $d018
        lda CP
        clc
        adc #$04
        sta CP
        bcc nocarry
        inc CP+1
nocarry:
        pla
        tay
        pla
        rti