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use gpsd and chrony time sync with fake gps


From: Lin Zhao
Subject: use gpsd and chrony time sync with fake gps
Date: Wed, 10 Nov 2021 21:56:15 -0500


Hi,
Thanks for providing this mail-list. I am using microcontroller as a fake GPS in our project for time sync in gps-denied environment.

The microcontroller generates PPS and NMEA messages to Nvidia Jetson computer running Ubuntu 18.04. The PPS is stable as tested in Oscilloscope. The NMEA message is copied from a real gps record.

I followed the tutorial in Feeding chrony from GPSD,

/etc/chrony/chrony.conf:
pool ntp.ubuntu.com           iburst maxsources 4
pool 0.ubuntu.pool.ntp.org iburst maxsources 1
pool 1.ubuntu.pool.ntp.org iburst maxsources 1
pool 2.ubuntu.pool.ntp.org iburst maxsources 2
driftfile /var/lib/chrony/drift
allow
# set larger delay to allow the NMEA source to overlap with
# the other sources and avoid the falseticker status
refclock SOCK /var/run/chrony.ttyTHS0.sock refid GPS precision 1e-1 offset 0.9999
refclock SOCK /var/run/chrony.pps1.sock refid PPS precision 1e-7  
Start commands:
sudo killall -9 gpsd chronyd
sudo chronyd -f /etc/chrony/chrony.conf
sleep 2
stty -F /dev/ttyTHS0 speed 9600
sudo gpsd /dev/ttyTHS0 -F /var/run/gpsd.sock

cgps -s result:
cgps.png
chronyc sources -v result:
chronyc.png
sudo ppstest /dev/pps1 result:
ppstest.png

Everything looks good, gpsd can parse the NMEA right, PPS is showing good. But chrony is not working. 

Any suggestions will be great, thank you so much!

Best regards,

-------------------------------------------------
Lin Zhao


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