[USRP-users] problems with ETTUS B200 and maximum clock rate

Marcus D. Leech mleech at ripnet.com
Fri Oct 24 12:58:32 EDT 2014


On 10/24/2014 10:29 AM, massimo zampetti via USRP-users wrote:
> Hi,
> I'm using an ETTUS B200 connected to my PC (USB 3.0 port:***Intel 
> Z7**7*, motherboard: *ASRock Z77 Extreme 11*,**OS: *Microsoft Windows 
> 7 (64 bit)*).
>
> I'm trying to use my SDR with a clock rate of *56 MHz* but it doesn't 
> work.
> I  did some tests both with GNURadio and with tx_waveforms.exe.
>
> About tx_waveforms contained in UHD directory, I modified its code to 
> add 'usrp->set_master_clock_rate()' and set its argument to 56 MHz.
> I set also the argument of 'usrp->set_clock_source()' to 56 MHz. Then 
> I run the code.
>
> The result shown on the command prompt is 'UUUU..' (Usrp Underrun).
> I obtained the same result with GNURadio.
>
> At the beginning I thought I could set clock rate up to 61.44 Mhz 
> (according to the maximum sample rate of DAC: 61.44 MS/s).
>
> I did some tests and here there are the results:
>
> 1.
>
>
>
> 2.
> set_master_clock_rate : 61.44 MHz
> set_clock_source: 56 MHz
>
>
>
> 2.
> set_master_clock_rate : 70 MHz
> set_clock_source: 56 MHz
>
>
>
> Where is the problem? Any suggestions?
>
> Regards,
>
> Massimo
>
>
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
I'll comment that the 'U' is due to underrun--your machine simply can't 
keep up with the demand of the USRP for samples at that rate.

Also, set_clock_source() is used to set whether the device derives its 
master clock from the on-board oscillator, or GPSDO, or external 10Mhz 
input.
   It makes no sense to pass it 56Mhz.

If you're just sending a narrowband tone, there's zero reason to send it 
at a very-high sample rate.


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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20141024/ba3449bf/attachment-0002.html>


More information about the USRP-users mailing list