RE: Underruns causing USRP to stop transmitting and receiving

[Jerrid Plymale]

Marcus,

Thanks for the response, but here are some of the issues with some of your 
suggestions. First off, this is a project I am working on for the company I 
work for, so I don't believe I can share the entire script with you in a public 
format as this discussion list set up as, so I am limited in that aspect. 

Second, I am using the function probes because I have tried to use message 
passing before but I have never been able to get it to work, and no one has 
been able to give me a simple tutorial on how to create message sinks that I 
can use to display variables in the GUI in real time. Also, the available 
instructional information that GNU Radio has put out for message passing is not 
in depth enough for me to figure out writing my on message sink blocks.

Finally, We are developing this system using Python due to is ease of quick 
development and our teams familiarity with it. I have very little experience 
writing C++, as do the others working on this project with me. On top of that I 
do not have a software background, so trying to re write all of this code in 
C++ while having to teach myself C++ at the same time while having less than 
two months left on this project to get the system to a functional state  is not 
really feasible.

I will also add that I am irritated with this as the mentioned analysis 
functions are the only ones having problems, we have other machine learning 
based analysis functions using the tensorflow python library that work without 
issue in the work function, even though the computational workload of the 
machine learning is greater than that of a couple summation and averaging 
functions, at least I would imagine.

Best Regards,

Jerrid 

-----Original Message-----
From: Marcus Müller <marcus.mueller@ettus.com> 
Sent: Wednesday, October 21, 2020 12:14 PM
To: Jerrid Plymale <jerrid.plymale@canyon-us.com>
Cc: Discuss Gnuradio <discuss-gnuradio@gnu.org>
Subject: Re: Underruns causing USRP to stop transmitting and receiving

Hi Jerrid,

thanks for the answer!

Let me have a couple of comments, just quickly, in no particular order:

* If in doubt, send code as code instead of as screenshot. These screenshots 
tell me very little about your software - and they don't really show me the 
parts of the code I'm interested in.
  I advised some students at uni. The first thing I require them to do is put 
their stuff on a git repository that I can access. That way, they can always 
tell me what to look at when they have a question. I found this is also a 
crucial technique for development outside of an academic setting!

* A function probe is really a kludge in GNU Radio and probably shouldn't be 
used. You've got very many of these - and that kind of hints at architectural 
problems, e.g. you trying to replace message passing with polling. My wild 
guess is that you've found a tutorial that advertises the function probe. 
Really, that's not meant for signal processing / marshalling purposes.

* Yeah, don't do time-critical signal processing in Python. As (the
other) Marcus mentioned, Python in this usage is orders of magnitude slower 
than just writing this in C++.

So, recommendations:

1. Get rid of **all** the function probes. It's not clear why you'd want that - 
really, it seems to me that you want to emit a new channel power estimate e.g. 
every 10000 samples. That should be a very normal decimating block!
2. In case you don't want to produce output regularly, you'd go with message 
passing, or with tagging the estimate to a sample on your estimator's output 
stream whenever appropriate (e.g. after receiving a message "please estimate 
this and that now"). Tagging would allow you to actually know which sample an 
estimate belongs to.
3. Python -> C++ if still necessary (quite possible)


Best regards,
Marcus

On 21.10.20 20:58, Jerrid Plymale wrote:
> Marcus,
>
> We are analyzing the average channel power of the USRP, as well as checking 
> to see if the signal received is a constant envelope signal, and a handful of 
> other functions like narrowband detection and pulsed signal detection. Here 
> is a screenshot of the flowgraph:
>
> [A picture containing graphical user interface  Description 
> automatically generated]
>
> And here is a snippet of the average channel power estimator function 
> (disregard the function name as that needs to be changed):
>
> [Text  Description automatically generated]
>
> So when this function is executed inside the work function of an embedded 
> python block, the application underruns, spitting out U's into the terminal 
> window. If instead we execute the function outside of the work function, as 
> shown below, the application doesn't underrun.
>
> [Text  Description automatically generated]
>
> And so the function being used above to execute the average channel power 
> estimator is being polled at a 10 Hz rate by a function probe. So are the 
> underruns due to polling rate difference between the work function and the 
> function probe? Is it something else? Any ideas on how I can get to work in 
> the work function without underrunning?
>
> Best Regards,
>
> Jerrid
>