Re: [gpsd-users] GPS Time Synchronization

[Burton, John]

Hi John!

Thanks for the reply! I think my original question was a bit confusing - I already use Chrony to adjust the system clock based on input from GPSD (so GPSD and CHRONYD are working together just fine). The question / issue is that GPSD+CHRONYD set the system clock to UTC time, which has an Epoch basis of Jan 1, 1970. GPS has an Epoch basis of Jan 6, 1980 (I think). Also, GPS does not deal with leap seconds, UTC does deal with leap seconds. Since I am getting data from an external INS/GPS unit, which provides a GPS timestamp (double precison seconds from the beginning of the week, and week since the epoch), and this external unit uses the same GPS receiver as my computer, I need to somehow provide the same timestamp for all the other data I am capturing. My question is, how can I do that?

John 

On Fri, May 19, 2017 at 9:30 AM, John Klug <address@hidden> wrote:

ntpd is what we use.  crony is also a possibility.  The PPS and GPS information are in separate shared memory locations, and with ntpd, these are configured as IP addresses.

Here is our ntp.conf patch file for default ntp usage:
http://git.multitech.net/cgi-bin/cgit.cgi/meta-mlinux.git/tree/recipes-support/ntp/files/ntp.conf.patch

John Klug
Senior Software Engineer

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From: gpsd-users [gpsd-users-bounces+john.klug=address@hidden] on behalf of Burton, John [address@hidden]
Sent: Thursday, May 18, 2017 6:21 PM
To: address@hidden
Subject: [gpsd-users] GPS Time Synchronization

Hi All!
I have what might or might not be an easy question.

  *   I have a computer running RedHat Enterprise Linux 7.3 that has GPS reciever attached to it that also provides a PPS signal. This computer is used as a real-time data acquisition system.
  *   I have configured the computer as described in http://catb.org/gpsd/gpsd-time-service-howto.html<http://mail2.multitech.com:32224/?dmVyPTEuMDAxJiZmNGMyMWQ1OTU4MTk2ZWViNj01OTFFMkM4Ml82NTIwMF85MTlfMSYmNjE3ZWE3MjRiMWVhNjEyPTEzMzMmJnVybD1odHRwJTNBJTJGJTJGY2F0YiUyRW9yZyUyRmdwc2QlMkZncHNkLXRpbWUtc2VydmljZS1ob3d0byUyRWh0bWw=> to operate as a network clock. This works fine.
  *   One of the devices I am capturing data from is an INS/GPS system that provides a position and pointing data packet with a GPS timestamp (week since GPS epoch + seconds into the week).
  *   I also have other devices that I am acquiring data for that I am attaching a timestamp to. I am currently using the boost::chrono::system_clock::now().
  *   I need to have all captured data using the same clock basis for the timestamp.
  *   How do I get GPS timestamp from my system clock?

John

--

John Burton, Ph.D.
MTEQ, Inc.

10440 Furnace Rd., Suite 204            Office:   540-658-2720 x1407
Lorton, VA 22079-2630                      Mobile: 757-508-6208
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--

John Burton, Ph.D.
MTEQ, Inc.

10440 Furnace Rd., Suite 204            Office:   540-658-2720 x1407
Lorton, VA 22079-2630                      Mobile: 757-508-6208
address@hidden                            Fax:     540-288-2515

 

Please note that the contents of this email including all attachments may be privileged or confidential in nature and are intended solely for the named recipients.  If you have received this message in error, please contact the sender immediately and be aware that the use, copying, or dissemination of this information is prohibited.