Hardware Options:

• USB GPS Stick: A simple u-blox 7 USB stick.
• LiNK500 Interface: Use the built-in GPS module by connecting a GPS antenna.

Step 1: “Pinning” the Hardware (udev Rule)

To avoid the “USB port lottery” where your device might jump between /dev/ttyACM0 and /dev/ttyACM1, we create a permanent alias.

1. Identify your device:
   lsusb
   Look for ID 1546:01a7 (standard for u-blox 7).
2. Create the rule file:
   sudo nano /etc/udev/rules.d/99-gps-device.rules
3. Paste this exact line:

   KERNEL=="ttyACM*", ATTRS{idVendor}=="1546", ATTRS{idProduct}=="01a7", SYMLINK+="gps-device"

4. Save and exit (Ctrl+O, Enter, Ctrl+X), then activate:
   sudo udevadm control --reload-rules && sudo udevadm trigger

Check: ls -l /dev/gps-device should now point to your ttyACM device.

Step 2: Installing the Tools

We use gpsd for the data and chrony to manage the clock.

sudo apt update
sudo apt install gpsd gpsd-clients chrony -y

Disable the automatic start to keep the system clean when no stick is plugged in:

sudo systemctl stop gpsd.socket
sudo systemctl disable gpsd.socket

Step 3: Configuring Chrony

1. Open config: sudo nano /etc/chrony/chrony.conf
2. Add these lines to the very end of the file:

   # GPSD shared memory driver for time sync
   refclock SHM 0 poll 2 refid GPS precision 1e-1 offset 0.1 delay 0.2
   
   # Allow immediate time jumps
   makestep 1.0 3

3. Restart chrony: sudo systemctl restart chrony

Step 4: The “Sync Button” Script

1. Create the script: nano ~/gps-sync.sh
2. Paste the following code:

   #!/bin/bash
   echo "--- GPS Time Sync (Handwerker-Style) ---"
   
   # Clean up
   sudo killall gpsd 2>/dev/null
   
   # Check for device
   if [ ! -L /dev/gps-device ]; then
       echo "ERROR: GPS device (/dev/gps-device) not found!"
       exit 1
   fi
   
   # Start GPSD
   echo "Starting GPS service at /dev/gps-device..."
   sudo gpsd /dev/gps-device -F /var/run/gpsd.sock
   
   echo "Waiting for GPS Fix... (Needs clear view of sky)"
   
   # Wait for valid data
   timeout 60 gpspipe -w | grep -m 1 "TPV" > /dev/null
   
   if [ $? -eq 0 ]; then
       echo "GPS Fix OK! Syncing system time..."
       sudo chronyc makestep
       echo "--- SUCCESS: Time is synchronized! ---"
       echo ""
       echo "Current GPS Data (Press 'q' to exit):"
       sleep 2
       cgps -s
   else
       echo "TIMEOUT: No GPS fix after 60 seconds."
   fi

3. Make it executable: chmod +x ~/gps-sync.sh

Step 5: The Menu Entry

To start the sync conveniently from your desktop menu:

1. Create the desktop file: nano ~/.local/share/applications/gps-sync.desktop
2. Paste the following content:

   [Desktop Entry]
   Name=GPS Time Sync
   Comment=Sync system time via GPS
   Exec=lxterminal -e "bash -c '/home/pi/gps-sync.sh; echo; echo Press any key to close...; read -n 1'"
   Icon=preferences-system-time
   Terminal=false
   Type=Application
   Categories=Utility;HamRadio;

   (Note: Verify if your user path is /home/pi/ or adjust accordingly.)

How to use it

• At Home: Chrony uses your Internet connection automatically. No manual action required.
• Off-Grid: Plug in the GPS (or connect antenna to LiNK500), click the icon in the menu, and wait for the “SUCCESS” message. Once your coordinates appear, press ‘q’ and start your Ham Radio software.