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Re: [Discuss-gnuradio] Mulitple USRP Stream Confusion

From: Daigle, Andrew - 1008 - MITLL
Subject: Re: [Discuss-gnuradio] Mulitple USRP Stream Confusion
Date: Wed, 1 Oct 2014 12:54:30 +0000

Hello Martin,

Thanks for the response. 

I should have mentioned that the subdev spec was set to A:A B:A because I am 
using the basic RX boards. Trying "0:A 0:B" instead gives the following error: 
"0:A is not a valid rx subdevice specification on mboard 0. possible values 
are: [A:AB, A:BA, A:A, A:B, B:AB, B:BA, B:A, B:B]."

Your suggestion to set the channel as 0,1,2,3 seemed to work perfectly (not 
sure how I missed that) as now I am getting four complex shorts out of my setup 
(an example of what is now in the buffer is shown below):


In getting the channels to stream however, I ran across another strange 
occurrence. After looking at the FFT data it appears as though the following 
commands only set the frequency of the first channel:

uhd::tune_request_t tune_request(freq);

Channels 1,2, and 3 all show single peaks centered at 0 Hz in the FFT window. I 
was able to correct this by directly setting the frequency of each channel 
independently (as shown below) , but I was under the impression that when you 
create the usrp devices to begin with it should apply commands across all 

uhd::tune_request_t tune_request(freq);
usrp->set_rx_freq(tune_request, 0);
usrp->set_rx_freq(tune_request, 1);
usrp->set_rx_freq(tune_request, 2);
usrp->set_rx_freq(tune_request, 3);

Thanks again! This is really a great product and I look forward to getting more 
acquainted with what it can do.

From: address@hidden address@hidden on behalf of Martin Braun address@hidden
Sent: Tuesday, September 30, 2014 5:04 PM
To: address@hidden
Subject: Re: [Discuss-gnuradio] Mulitple USRP Stream Confusion

Hey Andrew,

First, that subdev seems off -- I'd assume it's something like "A:0
B:0"? Next, I'm not even sure what you mean you set the channels to
"0,1" on both devices. You should have 1 streamer, with a channel
setting of "0,1,2,3". The 'args' string seems correct.

Does this help?


On 30.09.2014 13:01, Daigle, Andrew - 1008 - MITLL wrote:
> Hello!
> I am having trouble trying to create a continuous stream of complex
> shorts from multiple (2) X310 USRPs (each running 2 channels) over a
> single 1gigE switch (at a very low sampling rate); currently it appears
> as though I can only stream from one USRP at a time and I can't seem to
> figure out why. I should note I don't have this problem running each
> USRP on its own dedicated network (but unfortunately that won't be
> possible moving forward).
> To date, I have been using the rx_multi_samples example provided with
> UHD (source 003.007.002). I don’t seem to have any issue connecting to
> both USRPs and setting the parameters via the args=”addr0=,
> addr1=” command. It is just that when I call rx_stream->recv
> only the lights on the USRP which was listed first in args turn on. The
> subdev spec and channel selection for each USRP is set to "A:A B:A" and
> "0,1" and the incoming data from rx_stream is two channels of complex
> shorts (not 4 like I would expect from 2 USRPs).
> Do I have to initiate the streams differently or am I missing something?
> Thanks!
> -Andrew
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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