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

Marcus D. Leech mleech at ripnet.com
Fri Oct 24 14:49:55 EDT 2014


On 10/24/2014 02:34 PM, Massimo Zampetti wrote:
>
> I want to set the clock rate to 56 MHz because I want to send an 
> impulse with a duration of 17 ns - 20 ns (approximately). For this 
> reason I need of a very fast sample rate.
>
SO, you're going to have to figure out how to keep your B200 "fed" at 
that very-high sample rate.  Maybe a pre-recorded sample set in memory or
  something similar.   The "U" indicates that your computer isn't 
keeping up, and that includes the entire "stack" from application, 
through the kernel,
   the USB drivers, etc.


> Il 24/ott/2014 18:58 "Marcus D. Leech" <mleech at ripnet.com> ha scritto:
>
>     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/20141024/81fa8b88/attachment-0002.html>


More information about the USRP-users mailing list