INT 21 - Greg Shenaut ASPITAPE.SYS - INTERFACE
        AX = 440Ch
        BX = device handle
        CH = category code
            07h tape (ASPITAPE.SYS)
        CL = function
            01h "mtop" - perform tape operation
            02h "mtget" - get tape status
            03h ignore end-of-tape errors
            04h enable end-of-tape errors
        DS:DX -> parameter block (see below)
Return: CF set on error
            AX = error code (see AH=59h)
        CF clear if successful
            DS:DX -> data block
Notes:  This device driver is a simple DOS interface to the Adaptec Advanced
          SCSI Programming Interface (ASPI).  It provides the following device
          names as access to the SCSI tape, 'RMTx' (rewind on close) and
          'NRMTx' (NO rewind on close) where x can go from 0 to 3.  There may
          also be the following names 'MTx' and 'NMTx' which default to 1024
          byte blocks.  The names may also have a '$' appended to try and make
          them unique from file names of 'RMT0' etc.
        once opend these devices must be put into RAW mode
SeeAlso: AX=4402h"ASPI"

Format of mtop parameter block:
Offset  Size    Description
 00h    WORD    operation code
                00h "MTWEOF" - write an end-of-file record
                01h "MTFSF" - forward space file
                02h "MTBSF" - backward space file
                03h "MTFSR" - forward space record
                04h "MTBSR" - backward space record
                05h "MTREW" - rewind
                06h "MTOFFL" - rewind and unload
                07h "MTNOP" - perform TEST UNIT READY
 02h    DWORD   repetition count

Format of mtget parameter block:
Offset  Size    Description
 00h    BYTE    ASPI host ID
 01h    BYTE    SCSI target ID
 02h    BYTE    SCSI logical unit number
 03h    BYTE    device parameters
                bit 0: drive must use fixed-block read and write
                bit 7: drive is an ASPI device
 04h    BYTE    current device state (see below)
 05h    BYTE    unit number within driver
 06h    WORD    fixed block blocksize
 08h    BYTE    last SCSI status
 09h    BYTE    last SCSI sense key
 0Ah    WORD    last SCSI opcode (packed)
                bits 0-7: SCSI operation (SCSI packet byte 0)
                bits 8-10: SCSI flags (SCSI packet byte 1)
                bits 11-12: ASPI "Direction Bits" (ASPI SRB byte 3)
 0Ch    WORD    residual bytes from SCSI opcode

Bitfields for current device state:
 bit 0  device currently opened in buffered mode
 bit 1  drive currently opened in nonbuffered mode
 bit 2  rewind drive on last close
 bit 3  drive has been written on
 bit 4  drive has been read from
 bit 5  next read will return 0 bytes
 bit 6  EOM will resemble EOF
 bit 7  drive may be busy rewinding

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