Re: [Discuss-gnuradio] GPS Time

[Jawad Seddar]

Hello Derek,

Thanks for your answer.

Unfortunately, this is the method I was referring to when I was talking about setting the time manually in a python interpreter (the only difference is that I was using the functions from gr-uhd that translate to the method you mentioned).

Is there a way of doing this directly from GRC?

It used to work out of the box when using a usrp_source or usrp_sink block from gr-uhd.

Regards,

Jawad

2016-01-08 19:31 GMT+01:00 Derek Kozel <address@hidden>:

Hello Jawad,

The UHD 3.9 release changed the default GPSDO behavior. UHD does not automatically synchronize device time to GPS time on initialization because it's not reliable during device start-up. I'm not 100% sure about GNU Radio's handling of these changes so will have to check before commenting on the behavior there.

Here is a method of reliably setting the time in your own code:

1)  Poll on usrp->get_mboard_sensor("gps_locked") until it returns true

2)  Poll on usrp->get_time_last_pps() until a change is seen.
3)  Sleep 200ms (allow NMEA string to propagate)
4)  Use "usrp->set_time_next_pps(uhd::time_spec_t(usrp->get_mboard_sensor("gps_time").to_int()+1));" to set the time
5)  Poll on usrp->get_time_last_pps() until a change is seen.
6)  Sleep 200ms (allow NMEA string to propagate)
7)  Verify that usrp->get_time_last_pps() and usrp->get_mboard_sensor("gps_time") return the same time.

Regards,

Derek

On Fri, Jan 8, 2016 at 4:50 AM, Jawad Seddar <address@hidden> wrote:

Hi all, 

Yesterday, I decided to update from GNU Radio 3.7.7.1 + UHD 3.8.4 to GNU Radio 3.7.9 + UHD 3.9.1.

I used pybombs and everything went well, my OOT modules compile and my blocks run just like they used to.

My issue comes from the time that is set on the USRP. It seems like the time on the device is not set to use the GPSDO. After doing some digging, I noticed that this commit might be responsible : https://github.com/EttusResearch/uhd/commit/f4f3ce2550aba933b5f4d310d82a42a41ce3f6a1 .

So I tried setting the time source as GPSDO on my USRP source block (in GRC) but that doesn't seem to be working. I still get something  (in the tens of thousands) that is way below what it should be (I get the time on the USRP by looking at the rx_time tag available at the beginning of a received sample stream).

If I run a python CLI and setup a usrp_source then set the time manually to the gps_time, then the time is somewhat correct. 

Am I missing a step when setting up my usrp_source in GRC?

Thanks,

Jawad

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