Re: [Discuss-gnuradio] Large Sample Spikes after Each Packet in tx_bursts Example

[Jason Tran]

Hi All,

After messing with the code, I think I figured out the problem. I think it's an issue of an underflow like Josh suggested.

tx_waveforms works just fine for me when I send a constant signal (the spikes disappear). However, when I add some extra lines to the loop that populates "buff" and sends it with things such as print statements or more counters, I start invoking underflows. After learning this, I cleared out as much overhead as I could in the packet sending loop in tx_bursts.cpp and found that the signal stabilized without the large sample spikes I posted about earlier. 

Maybe if I try to add high priority to the program, I can reduce underflow problems... 

-Jason 

---

From: Josh Blum <address@hidden>
To: Jason Tran <address@hidden>
Cc: "address@hidden" <address@hidden>
Sent: Monday, June 18, 2012 11:57 AM
Subject: Re: [Discuss-gnuradio] Large Sample Spikes after Each Packet in tx_bursts Example

On 06/18/2012 10:51 AM, Jason Tran wrote:
> Hi All,
>
> "If you are seeing transients at the beginning of a burst, thats
> probablythe half band filters. They are implemented in block ram and
> dont clear between bursts."
>
> I'm actually sending one burst of a very long length so I can emulate
> an always-on signal (i.e. I'm not letting tx_bursts actually send an
> EOB packet). However, I still get the large samples with suppressed
> samples around.  The number of samples between every large sample
> (363) is directly equal to the samples per buffer size. i.e. the size
> of buffs used when invoking tx_stream->send(buffs, samps_to_send, md,
> timeout);
>

Sounds like you made some modifications to the example: Maybe you are
seeing the result of an underflow, or the buffer isnt filled for all
nsamps, or something during the checking for burst ack code...?

Perhaps the tx_waveforms example will be a better demonstration of
continuous streaming for you.

Also, this is the gnuradio mailing list, so I am going to recommend the
gnuradio companion as a great way to get started w/ the hardware and get
a good feeling for its operation:
http://gnuradio.org/redmine/projects/gnuradio/wiki/GNURadioCompanion

-josh