Stratum 1 GNSS NTP Server running on a Raspberry Pi 2

These are the parts I have used.

• Raspberry Pi 2
• SparkFun ublox NEO-M9N
  • This Adafruit module is a good alternative
• Adafruit DS3231 RTC
• Some cheap Active GPS Antenna
• uFL to SMA Adapter Pigtail (Example)
• Pin Headers for the GNSS module (Soldering required)
• Some Male-to-Female DuPont Cables

Previously the BeagleBone Black SBC was used, check the beaglebone branch for more information.

1. Install packages:

sudo apt update
sudo apt install pps-tools gpsd chrony nginx php-fpm php-gd

2. Edit /boot/firmware/config.txt

• Uncomment dtparam=i2c_arm=on

• Add the following under [all]:

  # Overclock
  arm_freq=1000
  core_freq=500
  sdram_freq=500
  over_voltage=2
  # Serial, RTC, PPS
  enable_uart=1
  dtoverlay=i2c-rtc,ds3231
  dtoverlay=pps-gpio,gpiopin=18
  nohz=off

3. Edit /boot/firmware/cmdline.txt, remove console=serial0,115200

4. Reboot to apply changes.

5. Setup GPSd

• Edit /etc/default/gpsd. Use file in this repo as reference.

• Edit systemd service to start after chrony: sudo systemctl edit gpsd

  Add:

  [Unit]
  After=chrony.service
  

• Start GPSd:

  sudo systemctl disable --now [email protected]
  sudo systemctl mask [email protected]
  sudo systemctl enable --now gpsd
  systemctl status gpsd

• Check using gpsmon and cgps commands.

6. Setup Chrony

• Edit Chrony config files. Use file in this repo as reference.

• Start Chrony:

  sudo systemctl enable chrony
  sudo systemctl restart chrony gpsd
  systemctl status chrony

• Check using chronyc tracking, chronyc sources -v, and chronyc sourcestats -v commands.

7. (Optional) Setup nginx + php to serve webpage: /etc/nginx/ & /var/www/html.

The following webpages are included in this repo.

Shows current time + offset, similar to time.is (Requires serverDate.js.php).

Quick page that shows the output of the following commands: chronyc sources, chronyc sourcestats, chronyc tracking.

My setup is based off the following guides.

• https://austinsnerdythings.com/2021/04/19/microsecond-accurate-ntp-with-a-raspberry-pi-and-pps-gps/
• https://robrobinette.com/pi_GPS_PPS_Time_Server.htm
• http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html
• https://conorrobinson.ie/raspberry-pi-ntp-server-part-6/