Re: [Discuss-gnuradio] GPS Time

[Marcus Müller]

Hi Jawad,

look at the query_gpsdo_sensors example; we recently (3.9.2) overhauled that to show how to portably and reliably set the device time to GPS time.

The point is that "set_time_source" is a bit of a misleading name: it actually sets the timing *pulse* source, i.e. where the USRP gets its PPS from. The GNU Radio USRP blocks set the device time to 0, iirc.


Best regards,
Marcus

On 11.01.2016 11:42, Jawad Seddar wrote:

Hi Derek,

I set my USRP source block to use the GPSDO as a Time source, then set the Sync parameter to "Unknown PPS".

All it does is reset the USRP tilme to 0 on the PPS front, it doesn't set the time to the GPS time.

Is there anything else I can try?

In the meantime, I reverted to UHD 3.8.5 which works for me.

Regards,

Jawad

2016-01-08 20:10 GMT+01:00 Jawad Seddar <address@hidden>:

Thanks Derek, I will try that when I get a chance.

I didn't try setting the "Sync" parameter to "Unknown PPS" but was guessing it might have something to do with that.

I will give it shot on Monday.

Regards,

Jawad

2016-01-08 20:07 GMT+01:00 Derek Kozel <address@hidden>:

Hi Jawad,

I believe that setting the USRP Sink block's setting to:

Clock: O\B GPSDO

Sync: Unknown PPS

is all that's needed but I do not have the hardware in front of me to verify this at the moment. I hope someone will chime in with confirmation or the correct settings, but I will check this when I get a chance, but it may not be until Monday.

Regards,

Derek

On Fri, Jan 8, 2016 at 10:40 AM, Jawad Seddar <address@hidden> wrote:

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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