Re: USRP N210 growing latencies

[Fabien PELLET]

Hi Marcus,

How to increase the size on the buffer at the output of the USRP source ?

Improve my flowgraph : maybe possible but I already did some improvment 
? I cascade 3 Xlating FIR filter with growing decimation (5, 10, 25) and 
already try to limitate the number of taps. I have to work with a 
12,5Msps source, make my duties at 10ksps and then output to the sink at 
200Ksps (the lowest value of the USRP). I tried XLating FFT filter but 
it was worst.

Thanks for your help,

Regards,

Fabien, F4CTZ.

Le 31/10/2021 à 13:03, Marcus Müller a écrit :
> Hi Fabien,
>
> risking sounding a bit cliché: Well, you need to fix your bug. The underflow 
> should not be
> happening!
>
> An easy solution, if this is just a manner of occasionally insufficient, but
> on-the-medium-term more-than-sufficient processing speed, a larger buffer 
> between the USRP
> source and the next block, maybe?
>
> Maybe we can otherwise help you improve the performance of your application :) 
> Just let us
> know!
>
> Best regards,
> Marcus
>
> On 30.10.21 00:20, Fabien PELLET wrote:
> > Hi,
> >
> > Thanks for the answer.
> >
> > At the moment, it seems that catching the underflow message and then 
> > lock/unlock the
> > flowgraph permits to reset the buffers and is enough for my application to get 
> > reasonnable
> > and not growing forever latencies. I don't if someone know a better way like a 
> > C++ method
> > that could do that more "elegantly".
> >
> > If I need more predictible latencies in the futur, indeed, I will try to use 
> > tags as you
> > suggest.
> >
> > Regards,
> >
> > Fabien, F4CTZ.
> >
> > Le 27/10/2021 à 17:02, Sylvain Munaut a écrit :
> > > Hi,
> > >
> > >
> > > > OK I understand that. But is there any solution which permits to reset that 
> > > > growing
> > > > propagation delay ? How to reset the flowgraph buffers without killing the 
> > > > application
> > > > and restart it ? Is there any method that permits to purge and resync buffers 
> > > > of the
> > > > flowgraph ?
> > > The USRP supports timestamps for RX and TX.
> > > So you get tags for when data was received / is supposed to be transmitted.
> > > Using a custom block to modify the RX tags into TX tags ( to change
> > > the RX timestamps to TX timestamps a bit into the future ), you should
> > > be able to achieve a constant controlled latency.
> > >
> > > Cheers,
> > >
> > >       Sylvain