FLAG    = $18000
STAT    = $18004
NREAD   = $18008
BUF     = $20000
CHUNK   = 65536          ; bytes per read
RECS    = CHUNK/256      ; 256-byte records per read
NCHUNK  = 16             ; 16 x 64KB = 1MB total

        org     $10000
start:
        move.l  #1,FLAG.l              ; signal: started
        move.l  #NCHUNK,d6
        moveq   #0,d5                  ; record position
        moveq   #0,d4                  ; completed count
loop:
        movem.l d4-d6,-(sp)
        moveq   #$46,d0                ; _B_READ
        move.l  #$80000000,d1          ; PDA=$80 (SASI unit0), mode=0
        move.l  d5,d2                  ; position (records)
        move.l  #CHUNK,d3              ; byte count
        lea     BUF,a1
        trap    #15
        movem.l (sp)+,d4-d6
        move.l  d0,STAT.l              ; last status
        tst.l   d0
        bmi.s   failed
        addq.l  #1,d4
        move.l  d4,NREAD.l
        add.l   #RECS,d5
        subq.l  #1,d6
        bne.s   loop
        move.l  #$FF,FLAG.l            ; signal: done OK
stop:   bra.s   stop
failed:
        move.l  #$EE,FLAG.l            ; signal: error
        bra.s   stop