[Discuss-gnuradio] Howto transmit idle pattern output when data isn't available

[Phelps Williams]

I have what I would suspect is a common dilemma with the gnuradio architecture.  I have a udp socket which is providing me a packets at less than the bitrate being transmitted by the usrp.  The datagrams being received by the udp socket are variable in size and message timing is not regular.

If my gnuradio transmitter exhausts the data available on the udp socket there will be a gap in the modulated output (I would expect the output of my usrp to just go CW at this point correct?).  This will definitely happen because the bitrate my modulator expects is higher than the actual amount of data available.  This causes the receiver to go out of bit lock and it must attempt to relock when modulation starts again.  

Is it possible to inject an idle pattern when datagrams are not available to keep the receiver in lock?  I'm thinking I may need to write my own source which does a non blocking read on the socket, if data isn't available it outputs an idle sequence, if data is available it provides that instead.  Is there an easier way to do this (that doesn't require me to do additional work)?

Thanks!

-Phelps