The TL820 family of libraries uses an Input/Output Device (IOD)
    to allow putting tapes into the library and taking them out. The
    inport part of the IOD holds a single cartridge and has a door on
    top which must be opened before a cartridge can be placed in it.
    A button on the front of the IOD opens the door, but only after
    it has been enabled by a Ready IOD command. This is a vendor
    unique command specific to the TL820 family.

    The mrd_ready_inport(3mrd) routine allows sending a Ready IOD
    command to the robot and port specified by the robot_name
    and inport arguments. For all currently shipping TL820 family
    libraries there is only one Inport, so the inport argument can
    always be "0". On a TL820, when the source for a move in the
    Inport, this routine should be called first and time allowed
    for the operator to place a tape in the inport. The routine mrd_
    move(3mrd) expects the element to be full when it starts.