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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

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,

pool           iburst maxsources 4
pool iburst maxsources 1
pool iburst maxsources 1
pool iburst maxsources 2
driftfile /var/lib/chrony/drift
# 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:
chronyc sources -v result:
sudo ppstest /dev/pps1 result:

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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