Re: [Discuss-gnuradio] USRP1 4 Channel Subdev Issue

[Tom Hendrick]

I tried the suggestion from Marcus and was able to get the USRP1 to work with 4 real channels.  I have a simple GRC script which  samples the USRP at 1MS/s and then resamples the signal to 500kS/s and then writes to a file.  I am getting continuous Overruns with this GRC script on my laptop. 

I have the same GRC script with the older GNURadio and when I ran it again on the same laptop (I booted up a prior version of ubuntu with an older gnuradio version that uses the USRP class not UHD) it writes to file with no Overruns at all.  I saw that the custom quad channel USRP block has an fusb_block and fusb_nblocks setting.  These are both set to 512*32 but if I lower them to something like 64*32 I start to see the Overruns.

Are there similar type settings I can adjust on the 3.6.2 version of GRC or GNURadio python scripts to get rid of the overruns?  I'm not sure if this is possible but I would like to not have to boot into an older ubuntu version when I need 4 real channels.  The only thing that comes to mind is to adjust noutput_items and I tried this but it didn't eliminate the overruns.

Thank you, -Tom

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From: Tom Hendrick <address@hidden>
To: Marcus D. Leech <address@hidden>; "address@hidden" <address@hidden>
Sent: Tuesday, February 19, 2013 11:19 AM
Subject: Re: [Discuss-gnuradio] USRP1 4 Channel Subdev Issue

Oh ok I will try that out not sure why I didn't come across that in my search.  Thanks so much Marcus!

-Tom

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From: Marcus D. Leech <address@hidden>
To: address@hidden
Sent: Tuesday, February 19, 2013 11:13 AM
Subject: Re: [Discuss-gnuradio] USRP1 4 Channel Subdev Issue

Hello all,

I am trying to make the USRP1 work with 4 independent real signal channels (not IQ) using two RX daughterboards.  In the older versions of GNURadio I was able to make this work with a custom block I had found in a repository or from somebody on the mailing list.

I am using GRC to make scripts and in the newer UHD version I'm having trouble making this work with 4 channels.  I can make 2 channels work by setting the Mb0:subdev specification in the UHD block to A:A A:B, or even A:B B:B, etc.

When I try to make all four work by setting A:A A:B B:A B:B (four independent real channels) I get the following error:

RuntimeError: ValueError: The subdevice specification "A:A A:B B:A B:B" is too long.
The user specified 4 channels, but there are only 2 rx dsps on mboard 0.

Does anyone know how I can properly call the subdevice specification and make this work without needing a custom block (I'm not skilled enough to write complicated blocks)? Again, in the older GNURadio version I was able to get 4 real RX channels to work independently with a custom block someone else had written.  I don't think its compatible with the newer UHD version as it was done in 2009.

Thank you, - Tom

For 4 RX DSPs on the USRP1, you need the 4rx FPGA image:

http://files.ettus.com/uhd_docs/manual/html/usrp1.html#specify-a-non-standard-image

-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

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