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Re: USRP N210 growing latencies

From: Fabien PELLET
Subject: Re: USRP N210 growing latencies
Date: Wed, 3 Nov 2021 09:58:20 +0100
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.2.1

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,


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

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

Best regards,

On 30.10.21 00:20, Fabien PELLET wrote:

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 
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


Fabien, F4CTZ.

Le 27/10/2021 à 17:02, Sylvain Munaut a écrit :

OK I understand that. But is there any solution which permits to reset that 
propagation delay ? How to reset the flowgraph buffers without killing the 
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.



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