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
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