Hi Marcus,

Thank you so much, it's working like a charm now!

Best,
Guy

On Wed, Jun 17, 2020 at 5:59 PM Marcus Müller <marcus.muel...@ettus.com>
wrote:

> Hi Guy,
>
> you don#t have to stop a flow graph to set the gain value. In fact, you
> shouldn't.
>
> Yes, you'll still have signal passing through your USRP while you're
> adjusting the gain, but that's exactly what timed commands are for.
>
> > I've heard about sending commands to the
> > USRP Sink, though I couldn't find any documentation on the subject and
> the
> > one page I found has been removed (and was never archived).
>
> Maybe you mean
> https://www.gnuradio.org/doc/doxygen/page_uhd.html
> ?
>
> That describes the commands you can send in both via asynchronous
> message passing, and via tags.
>
> > message I keep receiving from the flowgraph:
> >
> > gr::log :FATAL: tagged_stream_mux0 - Missing a required length tag on
> port
> > 1 at item #100
> > thread[thread-per-block[10]: <block tagged_stream_mux(14)>]: Missing
> length
> > tag.
> >
>
> that means you've set your USRP sink to tagged stream block mode, but
> then you sent in data that wasn't part of any tagged stream "blob".
>
> > It seems to happen at random with any tagged block in the flowgraph (the
> > point of failure typically changes every time we run it). While we could
> > theoretically just catch the error and restart the flowgraph,
>
> Uuuuh, that sounds like it won't *actually* work.
> > I would
> > rather find a more permanent solution. We're using two Ettus B200 SDRs
> for
> > our current tests.
>
> Yeah, use timed commands to set the gain. Use tags to add them to your
> sample stream. Don't use tagged stream blocks unless you actually want to.
>
> >
> > If anyone has any information on proper dataflow control for blocks or
> the
> > USRP sink message passing API, I'd really appreciate it.
>
> Best regards,
> Marcus
>
>

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