; lenser -- Apple //e Double Hi-Res boot loader + viewer (self-contained)
;
; Loads 16K to main $2000-$5FFF with ordinary reads (main half at $2000, aux half
; at $4000), then block-copies $4000-$5FFF into auxiliary $2000-$3FFF (RAMWRT on
; only for that clean copy, never during the boot-ROM reads), then turns on DHGR.
; ROM read at $C65C reads sector $3D into page $27 and re-enters $0801.
;
; assembled by apple/viewer/assemble.py via xa

        * = $0800
        .byte $01
entry:                          ; $0801, re-entered after each ROM read
        lda dpage
        cmp #$60                ; loaded $2000-$5FFF (64 pages)?
        bcs done
        lda psec
        cmp #$10
        bcc readit
        jsr seeknext
        lda #$00
        sta psec
readit:
        lda psec
        sta $3d                 ; desired sector
        lda curtrk
        sta $41                 ; desired track (the ROM read verifies BOTH)
        lda #$00
        sta $26
        lda dpage
        sta $27
        inc psec
        inc dpage
        ldx $2b
        jmp $c65c

done:
        ; copy main $4000-$5FFF -> aux $2000-$3FFF
        lda #$00
        sta $06
        lda #$40
        sta $07                 ; src = $4000
        lda #$00
        sta $08
        lda #$20
        sta $09                 ; dst = $2000
        sta $c005               ; RAMWRT on (writes go to aux)
        ldx #$20                ; 32 pages
cpl:
        ldy #$00
cp1:
        lda ($06),y
        sta ($08),y
        iny
        bne cp1
        inc $07
        inc $09
        dex
        bne cpl
        sta $c004               ; RAMWRT off
        ; turn on Double Hi-Res
        lda $c050               ; graphics
        lda $c052               ; full screen
        lda $c054               ; page 1
        lda $c057               ; hi-res
        sta $c00d               ; SET80VID (write-triggered switch -- must STA)
        sta $c05e               ; SETDHIRES (write-triggered)
#include "awyt.i"

; advance the head one track (two half-steps) with the standard phase-overlap
; seek.  energize the NEXT phase while the current one is still on (this pulls
; the head smoothly), then release the old phase, using on/off settle delays
; from an acceleration table indexed by step number ($0a).  the final phase is
; released before reading.
seeknext:
        inc curtrk              ; now on the next track
        lda #$00
        sta $0a                 ; step index for the timing table
        jsr onestep
        jsr onestep
        lda halftrk             ; release final phase before the read
        and #$03
        asl
        ora $2b
        tax
        lda $c080,x
        rts
onestep:
        lda halftrk             ; energize NEXT phase (halftrk+1), old still on
        clc
        adc #$01
        and #$03
        asl
        ora $2b
        tax
        lda $c081,x
        ldx $0a
        lda ontable,x
        jsr wait
        lda halftrk             ; release OLD phase (halftrk)
        and #$03
        asl
        ora $2b
        tax
        lda $c080,x
        ldx $0a
        lda offtable,x
        jsr wait
        inc halftrk
        inc $0a
        rts
; Apple seek timing tables (head accelerates over a move, slow first step).
ontable:  .byte $13,$0a,$08,$06,$05,$04,$04,$03
offtable: .byte $46,$1a,$10,$0c,$0a,$09,$08,$08
wait:                           ; delay loop ~ proportional to A
        tay
w1:
        ldx #$00
w2:
        dex
        bne w2
        dey
        bne w1
        rts

psec:    .byte $01
dpage:   .byte $20
halftrk: .byte $00
curtrk:  .byte $00