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

[Tom Hendrick]

Thanks Josh.
I've tried some different combinations of uhd_usrp_probe --args="serial=123456, recv_frame_size=16384,num_recv_frames=16" and varied recv_frame_size up to something really high like 1,000,000 and num_recv_frames up to 400 and didn't get the segementation fault error. 

When I run my 4 channel RX script after trying some different configurations I am still getting overruns.  If I change the USRP sampling rate to 500kS/s but leave the file rate at 500kS/s the overruns go away however I want to sample the USRP at 1MS/s to have a flatter frequency response.  This leads me to think the Overruns are not caused by the file writing part.

The fusb_block and fusb_nblocks setting were both set to 512*32 in the older GNURadio version and custom USRP 4 channel source block.  The same script in the older GNURadio version still runs with no Overruns even at 1Ms/s for each of the 4 USRP channels.

Is there anything else I can try?  Do I need to also alter the send_frame_size and num_send_frames in the uhd_usrp_probe calls?

Thank you, Tom

---

From: Josh Blum <address@hidden>
To: Tom Hendrick <address@hidden>; "address@hidden" <address@hidden>
Sent: Wednesday, February 20, 2013 4:34 PM
Subject: Re: [Discuss-gnuradio] USRP1 4 Channel Subdev Issue

On 02/20/2013 02:22 PM, Tom Hendrick wrote:
> Thanks for the suggestion Marcus.
>
> I tried adjusting those settings by using the following command:
>
> uhd_usrp_probe --args="serial=123456, recv_frame_size=4096,num_recv_frames=4096"
> The 123456 is replaced with the actual serial number of the usrp1 when I run the command. 
>
>
> When I run that command it shows the USRP1 configuration settings and the daughtercard and then at the bottom it says "Segmentation fault (core dumped)".  This happens with other values of recv_frame_size and num_recv_frames.  Does anyone know what I'm doing wrong or is this even the right way to change those settings?
>
> What are the default values in case I need to set them back to what they were?  I couldn't find this anywhere in the UHD documentation.
>

The values arent sticky, so you dont need to worry about that. The
default libusb xfer size if 16384 bytes.

I think the segfault comes from the number of frames. The default is 16,
and you can change this, but 4k is probably way more pending LUTs than
libusb can handle.

-josh

> Thank you, - Tom
>
>
>
>
> ________________________________
>  From: Marcus D. Leech <address@hidden>
> To: Tom Hendrick <address@hidden>
> Cc: "address@hidden" <address@hidden>
> Sent: Wednesday, February 20, 2013 9:53 AM
> Subject: Re: [Discuss-gnuradio] USRP1 4 Channel Subdev Issue
> 
>
> 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
>>
>>
>>
>>
> http://files.ettus.com/uhd_docs/manual/html/transport.html#usb-transport-libusb
>
> The USB parameters shown there can be passed as device args
>
>
>
>
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