Ah! You've set the data type of the QT GUI sink to "complex message"; I
wasn't aware that this feature had made it to the master branch :)

> The point of moving to C++ was that the flowgraph I /really/ want to
> use is just causing me huge problems - most notably that there are
> periods of a few seconds every now and again when the USRP drops a
> load of packets and then, after a while, the flow just freezes up. I
> find it difficult to follow how GNU Radio really works and I thought
> it would be a better bet to be directly in control of my samples all
> the way.

Hm, yeah, I know it's not trivial, but I'm pretty sure this isn't the
way to go. What kind of flow graph was giving you so much trouble?


Best regards,

Marcus


On 08/03/2017 11:15 AM, Jack White wrote:
> Hi Marcus,
>
> Thanks for the response. I attach the flowgraph I am using for this
> test, and for which I got the "unknown data type of samples" error.
>
> I wasn't aware that the metadata was included in the PDUs, so that
> makes more sense now.
>
> The point of moving to C++ was that the flowgraph I /really/ want to
> use is just causing me huge problems - most notably that there are
> periods of a few seconds every now and again when the USRP drops a
> load of packets and then, after a while, the flow just freezes up. I
> find it difficult to follow how GNU Radio really works and I thought
> it would be a better bet to be directly in control of my samples all
> the way.
>
> Jack
>
>
>
> On Wed, Aug 2, 2017 at 10:45 PM, Marcus Müller via USRP-users
> <usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>> wrote:
>
>     Hi Jack,
>
>     PDUs are not just samples one after the other – they contain
>     metadata. I can't really imagine what your flow graph looks like,
>     so I'd be grateful for a screenshot (File->Screen Capture).
>
>     Anyway, there'd be no obvious reason your UDP detour would make
>     things faster – maybe the intermediate socket buffering might
>     help, but you'd probably get the same result by extending a UHD
>     USRP Source's Output Buffer Size.
>
>     So, I'm not sure where we should take this – from a gut feeling,
>     we should maybe move on to the discuss-gnuradio mailing list and
>     discuss what part in your GNU Radio application isn't performing
>     well enough – as I'm currently assuming your approach wasn't born
>     through an in-depth analysis, but might more be of a trial&error
>     iteration?
>
>     Best regards,
>
>     Marcus
>
>
>     On 02.08.2017 13:10, Jack White via USRP-users wrote:
>>     Hi,
>>
>>     I've been having some difficulty getting reliable data flow from
>>     my USRP X310 with a GRC flowgraph, so I'm trying out writing my
>>     system in C++ with the UHD driver API. My first step has been to
>>     retrieve samples from the X310, forward them to a UDP port and
>>     then pick them up with a GRC Socket PDU component and then plot
>>     them. The C++ programme, so far, follows Ettus's example
>>     rx_samples_to_udp almost exactly and uses the std::complex<float>
>>     data type.
>>
>>     When the data enters the running flowgraph from the UDP
>>     transport, I get this error:
>>
>>     thread[thread-per-block[1]: <block freq_sink_c (1)>]:
>>     freq_sink_c: unknown data type of samples; must be complex.
>>
>>     Can anyone offer insight into why this should occur?
>>
>>     Many thanks,
>>
>>     -- 
>>     Jack White
>>     white.n.j...@googlemail.com <mailto:white.n.j...@googlemail.com>
>>     07875 813 745
>>
>>
>>     _______________________________________________
>>     USRP-users mailing list
>>     USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com>
>>     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>     <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com>
>     _______________________________________________ USRP-users mailing
>     list USRP-users@lists.ettus.com
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>
> -- 
> Jack White white.n.j...@googlemail.com
> <mailto:white.n.j...@googlemail.com> 07875 813 745
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