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Configuring the time server

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For the ADAPT payload software, we use /dev/gps and /dev/spatial as names for the NMEA and Advanced Navigation Spatial hardware names (this avoids issues with ttyUSB0/1/2 etc. numbering). In order to set this up, you'll need to know the device IDs - usually found with the 'lsusb' command. For reference, the USB hardware we used look like this:

067b:2303 Prolific Technology, Inc. PL2303 Serial Port   # <- this is the 9-pin serial to USB converter
0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC  # <- this is the standard Spatial USB cable
Setup the udev rule
sudo nano /etc/udev/rules.d/99-zgps.rules
# copy and paste the info below (after changing the IDs to match your hardware)
SUBSYSTEM=="tty", ATTRS{idVendor}=="067b", ATTRS{idProduct}=="2303", GROUP="dialout",  SYMLINK+="gps"
SUBSYSTEM=="tty", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", GROUP="dialout", SYMLINK+="spatial"
Reload the udev rules to see /dev/gps and /dev/spatial
udevadm control --reload-rules && udevadm trigger

Required steps: configuring gpsd and chronyd

Disable the standard timesync

sudo systemctl stop systemd-timesyncd.service
sudo systemctl disable systemd-timesyncd.service
Disable standard gpsd startup since we may need to run it in debug mode
sudo systemctl stop gpsd
sudo systemctl disable gpsd
sudo systemctl stop gpsd.socket
sudo systemctl disable gpsd.socket
If you do need to run it in debug mode, issue these commands to test it and see output
sudo killall gpsd
sudo gpsd -D 5 -N -n -b /dev/gps /dev/pps0
note: the ADAPT payload software will start gpsd (refer to this for reference)

Configure chrony

sudo systemctl stop chronyd
sudo nano /etc/chrony/chrony.conf
# add/edit lines as shown below
# rtcsync  # note: turn this off to not use system clock
refclock SHM 0 refid GPS precision 1e-1 offset 0.045 noselect
refclock SHM 2 refid PPS precision 1e-7 prefer
Start chrony and review the sources
sudo systemctl start chronyd
chronyc sources
we want the PPS and GPS to show like this:
MS Name/IP address         Stratum Poll Reach LastRx Last sample
#- GPS                           0   4   377    12  +3580us[+3580us] +/- 101ms
#* PPS                           0   4   377    10    -86ns[ -157ns] +/- 181ns
Note: the * next to PPS

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