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
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