; lenser -- Atari static-playfield slideshow viewer (GR.15 / GR.9 / GR.8).
;
; 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 and showing each before advancing (key / seconds / both).
;
; DOUBLE BUFFERED so the previous slide stays on screen while the next loads (no
; blank between slides).  Two RAM buffers alternate as front/back --
;   buffer 0 -- bitmap $4000/$5000, colour bytes $6000
;   buffer 1 -- bitmap $7000/$8000, colour bytes $9000
; both kept below $A000 so they are RAM even when the BASIC ROM is enabled.  The
; display list's two LMS addresses point at the front buffer; each slide is SIO-
; read into the *back* buffer while the front (the previous picture) keeps
; displaying, then -- during a vertical blank so the change isn't torn -- the LMS
; addresses and colour registers are switched to it.  ss_hi = ssbuf*$30 is the
; high-byte offset ($00 buffer 0, $30 buffer 1) added to every buffer address.
;
; The mode is fixed for the whole slideshow, chosen by build-time #defines --
;   DLMODE    ANTIC mode byte ($0e GR.15, $0f GR.9/GR.8)
;   GPRIOR    GTIA priority/mode ($00, or $40 for GR.9)
;   COLORMODE colour-register layout (0 GR.15 / 1 GR.9 / 2 GR.8)
; plus WAITMODE/WAITSECS/RATE, NIMAGES, LOOPFLAG, BASESEC, SPI (see assemble.py).

colptr = $cb                    ; zero-page pointer to the back buffer's colours

        * = $2000
boot:
        .byte 0                 ; flags
        .byte 0                 ; sector count (patched by the ATR writer)
        .word $2000             ; load address
        .word binit             ; init address (DOSINI)

cont:                           ; $2006 -- OS JSRs here after loading the stub
        lda #<dlist
        sta $230                ; SDLSTL
        lda #>dlist
        sta $231                ; SDLSTH
        lda #GPRIOR
        sta $26f                ; GPRIOR
        lda #$00
        sta $22f                ; SDMCTL = 0 (blank before the first image only)
        sta ssidx
        sta ssbuf               ; first slide loads into buffer 0

ssmain:
        jsr sethi               ; ss_hi = ssbuf * $30
        jsr readimg             ; SIO-load image ssidx into the back buffer

        ; ---- wait for a vertical blank, then flip to the back buffer ----
        ; (the front buffer -- the previous slide -- has stayed on screen)
        lda $14
vbwait:
        cmp $14
        beq vbwait              ; RTCLOK ticked -> we are in the vertical blank

        ; display-list LMS -- region 1 = base, region 2 = base + $1000
        lda #$00
        sta lms1
        sta lms2
        lda #$40
        clc
        adc ss_hi
        sta lms1+1              ; $40 / $70
        lda #$50
        clc
        adc ss_hi
        sta lms2+1              ; $50 / $80

        ; colour bytes are at base + $2000
        lda #$00
        sta colptr
        lda #$60
        clc
        adc ss_hi
        sta colptr+1           ; $60 / $90
#if COLORMODE == 0
        ldy #$00
        lda (colptr),y
        sta $2c8                ; COLBAK  (value 0)
        ldy #$01
        lda (colptr),y
        sta $2c4                ; COLPF0  (value 1)
        ldy #$02
        lda (colptr),y
        sta $2c5                ; COLPF1  (value 2)
        ldy #$03
        lda (colptr),y
        sta $2c6                ; COLPF2  (value 3)
#endif
#if COLORMODE == 1
        ldy #$00
        lda (colptr),y
        sta $2c8                ; COLBAK = hue (GR.9)
#endif
#if COLORMODE == 2
        ldy #$00
        lda (colptr),y
        sta $2c6                ; COLPF2 background
        sta $2c8                ; COLBAK  border = background
        ldy #$01
        lda (colptr),y
        sta $2c5                ; COLPF1 foreground
#endif
        lda #$22
        sta $22f                ; SDMCTL on (a no-op after the first slide)

        jsr sswait
        lda ssbuf
        eor #$01
        sta ssbuf               ; next slide loads into the other buffer
        inc ssidx
        lda ssidx
        cmp #NIMAGES
        bcc ssmain
#if LOOPFLAG == 1
        lda #$00
        sta ssidx
        jmp ssmain
#else
        lda #$00
        sta $09                 ; clear BOOT? so warmstart enters BASIC
        jmp $e474               ; warm-start (exit)
#endif

binit:
        rts

; ss_hi = ssbuf * $30 (back-buffer high-byte offset -- $00 buffer 0, $30 buffer 1)
sethi:
        ldx #$00
        lda ssbuf
        beq sh0
        ldx #$30
sh0:
        stx ss_hi
        rts

; ---- SIO read SPI sectors of image ssidx into the back buffer (base+$0000) ----
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               ; DBUFLO = $00
        lda #$40
        clc
        adc ss_hi
        sta $0305               ; DBUFHI = $40 / $70 (back buffer base)
        lda #SPI
        sta cnt
rloop:
        lda #$31
        sta $0300               ; DDEVIC = disk
        lda #$01
        sta $0301               ; DUNIT 1
        lda #$52
        sta $0302               ; DCOMND R (read)
        lda #$40
        sta $0303               ; DSTATS = read direction
        lda #$1f
        sta $0306               ; DTIMLO
        lda #$80
        sta $0308               ; DBYTLO = 128
        lda #$00
        sta $0309               ; DBYTHI
        lda secn
        sta $030a               ; DAUX1 sector low
        lda secn+1
        sta $030b               ; DAUX2 sector high
        jsr $e459               ; SIOV
        clc
        lda $0304
        adc #$80
        sta $0304               ; buffer += 128
        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                ; clear CH
sw1:
        lda #$00
        sta $4d
        lda $2fc
        cmp #$ff
        beq sw1
        rts
#endif
#if WAITMODE == 2
        lda #$00
        sta $12
        sta $13
        sta $14                 ; reset RTCLOK
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                ; any key ends the slide
        lda $13
        cmp #>(WAITSECS*RATE)
        bcc sw3
        bne sw3d
        lda $14
        cmp #<(WAITSECS*RATE)
        bcc sw3
sw3d:
        rts
#endif

ssidx:  .byte 0
ssbuf:  .byte 0                 ; 0 or 1 -- which buffer the next slide loads into
ss_hi:  .byte 0                 ; ssbuf * $30 (back-buffer high-byte offset)
secn:   .word 0
cnt:    .byte 0

dlist:
        .byte $70,$70,$70       ; 24 blank scan lines
        .byte DLMODE+$40        ; LMS + mode
lms1:
        .word $4000             ; region 1 base (patched to the front buffer)
        .dsb 101,DLMODE
        .byte DLMODE+$40        ; LMS + mode
lms2:
        .word $5000             ; region 2 base (patched to the front buffer)
        .dsb 89,DLMODE
        .byte $41               ; JVB
        .word dlist