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)