[USRP-users] E310 GPSDO and PPS sync

Moritz Fischer moritz.fischer at ettus.com
Mon Apr 27 15:58:42 EDT 2015

Hi Jeff,

so the first issue is that gps time and gps position is not
implemented. I have a branch in review that uses gpsd as backend and
greatly improve on that front.
It's currently in review and I expect it to be in the next round of
beta images in a couple of weeks.

The failing time alignment is worrying. I'll have to look into that
one and see if I can reproduce it.

Sorry about the inconvenience,


On Mon, Apr 27, 2015 at 12:29 PM, Long, Jeffrey P. via USRP-users
<usrp-users at lists.ettus.com> wrote:
> I have a couple of questions regarding the time sync with the E310.
> If I run query_gpsdosensors it informs me that the GPS is locked the USRP is
> locked to the 10 Mhz ref but it says GPS and UHD Device time are NOT aligned
> last_pps…..Try re-running the program.
> It then informs me that NMEA strings are not implemented for this device.
> Does this mean that we won’t ever be able to set GPS time of day or it is
> just not implemented yet?
> My second question I guess is more of an observation with a final question
> as to whether it is supposed to be doing this. I am trying to get a E310’s
> transmit time aligned with GPS timing. Using the tx_timed_samples example I
> set up a simple experiment to transmit every second a small burst of
> samples. Since I want the tx burst to occur right on the 1 PPS I modified
> the tx_timed_samples to use set_time_next_pps instead of set_time_now so I
> could ensure that when I call send I can pass times that make the transmit
> burst occur on the PPS. For reference I set up a E110 with a GPSDO running
> the same code and verified that its GPS was locked. I should mention that we
> re-radiate GPS inside our lab. Then for sanity I fired up a symmetricom
> instrument that provides precision PPS and ref. Putting everything on the
> scope and triggering with the instruments PPS I verified that the E110s
> burst was popping out right on the PPS of the instrument.
> Now to the E310. In my first attempt I could never get the E310’s time to
> align with either of these two references. It would come up randomly each
> time. It said its GPS was locked etc and would run fine but it was never
> aligned. After trying a number of things we finally discovered that if we
> waited about 10 seconds and then called set_time_next_pps it would stick and
> the E310 would be locked with the other two systems.
> Being more of an FPGA guy and pretty familiar with the Ettus FPGA designs I
> noticed that there is something new in the E310 design called ppsloop.v. It
> looks like you are doing something more elaborate to bring in the PPS before
> you pass it on to the vita time stuff. Is it possible that it is taking
> longer than planned and calls to set_time_next_pps are not working till that
> PPS is up?
> In any event I have a work around but I would think that it should not take
> this long so I thought I would bring it to your attention.
> Thanks
> Jeff Long
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