mrbuffer/src/main.S

            rel
            typ   $B3
            dsk   main.l

            ; ensure 16-bit mode (unnecessary?)
            clc
            xce
            rep   #$30

            phk
            plb


*            sec
*            clc
            sep   #$30        ; a, m, x half bank

            lda   #$00
            pha
            plb

            lda   #$0000
            pha
            pld

                              ; direct acc for these?


*; toggle the softswitches; they don't take any values. some are only triggered
*; by writes, $C054 can be triggered by a read
            sta   $C000       ; disable 80 column store?

            sta   $C00C       ; disable 80 column hardware?!
            sta   $C050       ; set standard apple ii gfx mode
            sta   $C051       ; select text mode only. "only"?
            lda   $C054       ; select text page 1 (there are 2)
            lda   $C056       ; select "low res" graphics

            lda   #"H"
            sta   $0400
            lda   #"e"
            sta   $0401
            lda   #"l"
            sta   $0402
            lda   #"l"
            sta   $0403
            lda   #"o"
            sta   $0404
            lda   #" "
            sta   $0405
            lda   #"W"
            sta   $0406
            lda   #"o"
            sta   $0407
            lda   #"r"
            sta   $0408
            lda   #"l"
            sta   $0409
            lda   #"d"
            sta   $040A
            brk



; Important locations
SPEAKER     equ   $E0C030
PRODOS16    equ   $E100A8

            jsl   PRODOS16
                              ; This exit code is "device busy", why is it the only one
                              ; that works?!
            da    $29
            adrl  QP
            bcs   ERROR

ERROR       brk

QP          adrl  $0000
            da    $00