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
________________________________
From: Tom Hendrick <[email protected]>
To: Marcus D. Leech <[email protected]>; "[email protected]"
<[email protected]>
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
________________________________
From: Marcus D. Leech <[email protected]>
To: [email protected]
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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