NAME
    Flush -- clear all queued I/O requests for the parallel port

FUNCTION
    This command purges the read and write request queues for the
    parallel device. The currently active request is not purged.

IO REQUEST
    io_Message      mn_ReplyPort initialized
    io_Device       set by opendevice
    io_Unit         set by opendevice
    io_Command      CMD_FLUSH (08)