; lenser -- Apple II HGR slideshow loader + viewer (self-contained, no DOS).
;
; The Disk II boot ROM loads track 0 sector 0 to $0800 and JMPs $0801.  This
; loader reads ALL the slideshow's HGR images (NIMAGES * 32 sectors) contiguously
; into a RAM buffer from $4000 up (image i at $4000 + i*$2000), then cycles --
; copying each image into HGR page 1 ($2000), switching on graphics, and waiting
; (key / seconds / both) before the next.  Looping is RAM-only (no re-seek).
;
; #defines from the wrapper --
;   WAITMODE 1 key / 2 seconds / 3 both    WAITSECS seconds (~)   NIMAGES count
;   LOOPFLAG 1 wrap / 0 stop    ENDPAGE  one past the last buffer page ($40+N*$20)
;
; assembled by apple/viewer/assemble.py via xa

src   = $06                     ; zero-page copy pointers
dst   = $08
ssidx = $19

        * = $0800
        .byte $01               ; ROM scratch (boot sector byte 0)
entry:                          ; $0801, (re)entered after every ROM read
        lda dpage
        cmp #ENDPAGE
        bcs loaded              ; whole buffer read -> start the show
        lda psec
        cmp #$10
        bcc readit
        jsr seeknext
        lda #$00
        sta psec
readit:
        lda psec
        sta $3d
        lda curtrk
        sta $41
        lda #$00
        sta $26
        lda dpage
        sta $27
        inc psec
        inc dpage
        ldx $2b
        jmp $c65c               ; slot-6 ROM read; reads a sector then JMP $0801

loaded:
        lda #$00
        sta ssidx
cyc:
        ; ---- copy image ssidx ($4000 + ssidx*$2000) -> HGR page 1 ($2000) ----
        lda ssidx
        asl
        asl
        asl
        asl
        asl                     ; ssidx * $20 pages (carry clear, <=4 images)
        adc #$40
        sta src+1               ; source hi = $40 + ssidx*$20
        lda #$00
        sta src
        sta dst
        lda #$20
        sta dst+1               ; dest = $2000
        ldx #$20                ; 32 pages
        ldy #$00
cpyl:
        lda (src),y
        sta (dst),y
        iny
        bne cpyl
        inc src+1
        inc dst+1
        dex
        bne cpyl

        lda $c050               ; graphics
        lda $c054               ; page 1
        lda $c057               ; hi-res

        jsr sswait

        inc ssidx
        lda ssidx
        cmp #NIMAGES
        bcc cyc
#if LOOPFLAG == 1
        jmp loaded              ; wrap (re-uses the ssidx=0 init at loaded)
#else
        lda $c051               ; text
        lda $c054
        jmp $e000               ; Applesoft cold start
#endif

; ---- wait (returns); clears the key strobe first ----
sswait:
        bit $c010
#if WAITMODE == 1
swk:
        lda $c000
        bpl swk
        bit $c010
        rts
#endif
#if WAITMODE == 2
        lda #WAITSECS
        sta $fd
so:
        lda #$03
        sta $fc
sm:
        ldx #$00
sx:
        ldy #$00
sy:
        dey
        bne sy
        dex
        bne sx
        dec $fc
        bne sm
        dec $fd
        bne so
        rts
#endif
#if WAITMODE == 3
        lda #WAITSECS
        sta $fd
bo:
        lda #$03
        sta $fc
bm:
        ldx #$00
bx:
        lda $c000
        bmi bdone               ; a key ends the slide
        ldy #$00
by:
        dey
        bne by
        dex
        bne bx
        dec $fc
        bne bm
        dec $fd
        bne bo
bdone:
        bit $c010               ; (also harmless on timeout)
        rts
#endif

; advance the head one track (two half-steps), phase-overlap step (from hgr.s)
seeknext:
        inc curtrk
        lda #$00
        sta $0a
        jsr onestep
        jsr onestep
        lda halftrk
        and #$03
        asl
        ora $2b
        tax
        lda $c080,x
        rts
onestep:
        lda halftrk
        clc
        adc #$01
        and #$03
        asl
        ora $2b
        tax
        lda $c081,x
        ldx $0a
        lda ontable,x
        jsr wait
        lda halftrk
        and #$03
        asl
        ora $2b
        tax
        lda $c080,x
        ldx $0a
        lda offtable,x
        jsr wait
        inc halftrk
        inc $0a
        rts
ontable:  .byte $13,$0a,$08,$06
offtable: .byte $46,$1a,$10,$0c
wait:
        tay
w1:
        ldx #$00
w2:
        dex
        bne w2
        dey
        bne w1
        rts

psec:    .byte $01              ; next physical sector (track 0 starts at 1)
dpage:   .byte $40              ; next destination page ($4000)
halftrk: .byte $00
curtrk:  .byte $00