Re: [Discuss-gnuradio] [USRP-users] B205mini half-duplex? (GRC)

On 07/05/2019 09:36 AM, Tom McDermott via USRP-users wrote:

Hi Marcus - thanks for the link to the documentation.  Messages don't have  the required functionality, so I have tried to insert tx_sob and tx_eob tags.  This unfortunately has not changed anything.  This is what the tag debug shows,  are these formatted correctly for UHD USRP sink?    ----------------------------------------------------------------------  Tag Debug:   Input Stream: 00    Offset: 139250  Source: burst_tagger4     Key: tx_sob   Value: #t  ----------------------------------------------------------------------    ----------------------------------------------------------------------  Tag Debug:   Input Stream: 00    Offset: 196587  Source: burst_tagger4     Key: tx_eob   Value: #t  ----------------------------------------------------------------------    

I have to stop streaming samples to the USRP Sink to get it to stop transmitting and  switch TX/RX over to RX - the tags aren't enough.  However the next time back to Tx,  the problem with transmitter underruns and weird oscillating T/R behavior resumes.    

Still looking for advice as to how to T/R switch the unit without the TX going nuts?    

-- Tom, N5EG    

Indeed, if there are ANY samples after a tx_eob, the USRP will go back into transmitting mode.

I'm copying the discuss-gnuradio mailing list, since this is really an issue of how to make tagged streams behave
  as-expected with GRC-derived flow-graphs.

I've never implemented a half-duplex TX scheme out of GRC myself, but there are folks on the discuss-gnuradio mailing list
  who have.

  On 07/04/2019 11:14 PM, Tom McDermott via USRP-users wrote:  > I am trying to use a B205mini in half-duplex mode through the TX/RX   > connector  > from a GRC flowgraph.  Gnuradio 3.7.13.4.  Very slow switching,   > manually implemented.  >  > The flowgraph implements a simple half-duplex transceiver. In order to   > switch  > the TX/RX antenna switch, I am starting and stopping samples to the   > USRP sink  > using the Copy block.  When the Copy block is enabled it passes   > samples to the USRP sink,  > and when disabled it does not copy samples to the USRP sink.  >  > If the Copy block is statically enabled, then the USRP transmits (RED   > led 'On' for TX/RX)  > continuously without any underruns.  >  > If the Copy is statically disabled, then USRP goes into receive mode   > (GREEN led 'On' for TX/RX)  > and stays in that mode.  >  > So far so good.  >  > However if I toggle the enable/disable on the copy block to disable   > the TX/RX switches as it should  > from red to green, but after I re-enable the Copy block and leave it   > enabled, the TX/RX  LED goes red  > for awhile, then rapidly flashes red/green/red etc. while printing   > UUUUUUU  on the GRC console, then  > goes RED for about 5 seconds without underruns, then flashes RED/GREEN   > rapidly for 5 or 10 seconds  > and underruns, back and forth ad infinitum.  >  > So Copy appears not to be a good way to implement T/R switching.  >  > There is a message port on the USRP sink block.  Can this be used to   > implement T/R switching?  > Is there some place that the messages that this port accepts defined?    > I cannot seem to find  > the syntax for the message definitions in the USRP documentation, so I   > must be looking in the wrong place.  >  > -- Tom, N5EG  >  >  There's some documentation here:    https://www.gnuradio.org/doc/doxygen/classgr_1_1uhd_1_1usrp__sink.html          

_______________________________________________  USRP-users mailing list  USRP-users@lists.ettus.com  http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com