[USRP-users] Still problems with USRP time from GPSDO

Marcus D. Leech mleech at ripnet.com
Mon Apr 29 17:01:17 EDT 2013


On 04/29/2013 04:55 PM, Josh Blum wrote:
>
> On 04/29/2013 03:51 PM, Marcus D. Leech wrote:
>> On 04/29/2013 04:08 PM, Josh Blum wrote:
>>> On 04/29/2013 01:56 PM, Sean Nowlan wrote:
>>>> On 04/29/2013 02:37 PM, Josh Blum wrote:
>>>>> Can I ask what version of UHD you are running? A few weeks ago I
>>>>> fixed a
>>>>> bug on the master branch related to GPSDO time,
>>>> Hi Josh, can you point me to that commit? was it just a fix to
>>>> query_gpsdo_sensors or something in the driver/gpsdo control code?
>>> It was a fix to the gpsdo control code:
>>>
>>> https://github.com/EttusResearch/uhd/commit/31f0e964aa54a2c8e4d299432513623d2c49bbf0
>>>
>>>
>>> -josh
>>>
>>> _______________________________________________
>>> USRP-users mailing list
>>> USRP-users at lists.ettus.com
>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>>
>>>
>> Is it not the case that GPS time is strictly-linear, whereas UTC (which
>> is what is carried by NTPD) has leap-second compensation.   Or do the GPSDO
>>    units produce a leapsecond-corrected timestamp?
>>
> The time in seconds in the GPGGA string as reported by the GPSDO unit is
> UTC time. So it should match the PC clock to the second. However, the
> GPS time is actually about 16 seconds off compared to UTC because it
> doesnt adapt with leap seconds.
>
> -josh
>
Here are some interesting notes with respect to GPS time-keeping 
functions on typical recievers, vs UTC (as delivered by NTPD).  Now, this
   makes me wonder how GPSD on Linux deals with this.

http://gpsinformation.net/main/gpstime.htm




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






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