Re: a const time offset ahead
Bill Unruh <[email protected]>
| Newsgroups | gmane.comp.time.chrony.user |
|---|---|
| Message-ID | <[email protected]> |
PPS has no "seconds" associated with it. It just blips exactly ( to withing a few ns) on the second. It gets its "seconds" from nmea. It would help if you gave a complete list for example of the sources command. It looks to me like you told it that PPS is off time (ie tried to correct the PPS time rather than the NMEA time) It is the NMEA time that will be off, but .2-.5 seconds usually (late) because the nmea sentence are sent out after the second, are sent out when the gps is not busy, and take a long time to get to the computer( it takes a while for the nmea sentence to be transmitted). But you have a home grown setup, so the problem could well be in there. How do you hook up the microcontroller, how does it send out the PPS to make sure it is on the UTC second, How is the NMEA generated, etc.? Are you telling chrony that teh PPS is late? William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273 Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324 UBC, Vancouver,BC _|_ Program in Cosmology |____ [email protected] Canada V6T 1Z1 ____|____ and Gravity ______|_ www.theory.physics.ubc.ca/ On Tue, 8 Mar 2022, Lin Zhao wrote: > [CAUTION: Non-UBC Email]Hi, > > I am using a microcontroller to generate PPS and NMEA string to time sync an Nvidia Jetson > computer using gpsd and chrony for the GPS-denied environment. PPS and NMEA are verified > as good. > > When I started time synchronization process, chrony always like: > #* PPS 0 0 1 0 -894ms[ -894ms] +/- 1000ns > > I tried a lot of times, chrony always considers PPS time is ahead around 890 ms. But I > checked the NMEA time data is right. When the computer is synchronized, system time is > ahead of NMEA time. Before the time synchronization, both of them are verified the same. > > After the 1 hour test, time is synchronized, but with this const offset. > > Could you tell me how to debug this? Thanks for your help. > > Best regards, > > -------------------------------------------------Lin Zhao > > Research Assistant @ Graduate School of Oceanography > Ph.D. Student @ Department of Ocean Engineering > University of Rhode Island > > Room 2, Horn Lab > 215 South Ferry Road > Narragansett RI 02882 > Phone: 401-771-4661 > E-mail: [email protected] > Personal: [email protected] > Lab: https://soslab.wordpress.com/ > >