30 June 2025 UPDATE: The fix outlined here seemed to work, but I noticed that some things were not right yesterday. I dug in deeper and I seem to have it working now. It appears that gpsd may have been the problem from the start. Below is a Copilot session that seemed to zero in on gpsd and the need to build a newer version.
Copilot session to fix GPS: PDF (430 KB)
After applying the changes, I tested three times and each time the correct location was identified, yes that was an issue, and the GPS had a fix in a reasonable time.
- Uptime 11 Minutes to fix (reboot)
- Uptime 9 Minutes to fix (reboot)
- Uptime 21 Minutes to fix (shutdown, power removed, sat for a few minutes and restarted)
The rest of this post is here for information only. I plan to write another post once I test on another SD Card.
I purchased a WWZMDiB VK-172 USB GPS Dongle Receiver from Amazon to use with my Raspberry Pi Photobooth but ran into some issues with it. The Raspberry Pi recognized the GPS module straight away but I noticed the GPS was not getting a location fix even when it was outside with a clear view of the sky. I had read that some people had a similar issue or it would take nearly an hour or longer to get a fix on the location. Obviously this is not acceptable. My experience with u-blox products is that their products are very good, so this was not normal. Something else must have been amiss.
For context, I had already installed and configured gpsd on the Pi, using tools like cgps and xgps for monitoring. The cgps application appeared that everything was working, but it was not getting a fix.
To verify that the GPS could obtain a location fix and how long it would take, I connected the GPS to my Windows PC and installed the u-blox u-center software. On the Windows PC, I was able to get a location fix quickly. This helped me to target the configuration on the Raspberry Pi.
Back on the Raspberry Pi, I looked at several things but suspected that the GPS unit was not configured properly. With the help of Copilot, I attempted to resolve the issue. What I uncovered is the GPS was not configured to send the proper NMEA messages.
I was able to properly configure the GPS to send NMEA messages but the GPS unit would not retain the configuration as it has no battery. I was able to write a script to run as a service and run on startup. All seemed to work well, but I needed to leave it and come back the next day. When I tested it again, things were no longer working as expected. Upon further investigation, it was noted that unplugging the USB GPS dongle and plugging it back in got everything working as expected.
I was able to land on a solution that mimicked the unplugging and plugging the dongle in. This final configuration seems to allow the dongle to work properly on the Raspberry Pi. I have not verified, but other Raspberry Pi versions may or may not have this issue.
Below is the list of steps necessary to get the GPS module to work properly with gpsd on the Raspberry Pi.
My setup
- Raspberry Pi 3
- Raspbian bookworm
- All updates applied as of 28 June 2025
Steps
- Update the Raspberry Pi OS and install packages by running the following code.
- sudo apt update -y && sudo apt upgrade -y
- Install gpsd and related packages
- sudo apt -y install gpsd gpsd-tools gpsd-clients
- Install Python GPS client library
- sudo apt install python3-gps
- Configure gpsd
- sudo nano /etc/default/gpsd
- Edit the file to include the following content
DEVICES="/dev/ttyACM0" USBAUTO="true" GPSD_OPTIONS="-n"
- Enable and start gpsd service
- sudo systemctl enable gpsd
- sudo systemctl start gpsd
- Reboot to ensure all changes take effect
- sudo reboot now
- Create the following script at /home/pi/setup-gps.sh to configure the USB GPS dongle on startup.
- nano /home/pi/setup-gps.sh
#!/bin/bash
# VK-172 USB GPS dongle was having issues sending messages
# dmesg | tail -n 20
# Showed that the USB Bus was having with dwc_otg_hcd_urb_dequeue
# The following commands mimic unplugging the USB and plugging it back in.
# Look for a serial device with 'u-blox' in the ID string
DEVICE_PATH=$(readlink -f /dev/serial/by-id/*u-blox*)
# Extract the most specific USB path (e.g. 1-1.3)
USB_ID=$(udevadm info -a -n "$DEVICE_PATH" | awk -F'"' '/KERNELS=="1-/ { if ($2 !~ /:/) { print $2; exit } }')
# Log what we found (optional for debugging)
echo "Reinitializing USB device at $USB_ID"
# Rebind to simulate replug
echo "$USB_ID" > /sys/bus/usb/drivers/usb/unbind
sleep 1
echo "$USB_ID" > /sys/bus/usb/drivers/usb/bind
sleep 5 # wait for USB to settle
ubxtool -f /dev/ttyACM0 -P 14 -p CFG-MSG,240,0,1 # GGA
ubxtool -f /dev/ttyACM0 -P 14 -p CFG-MSG,240,4,1 # RMC
ubxtool -f /dev/ttyACM0 -P 14 -p CFG-MSG,240,2,1 # GSA
ubxtool -f /dev/ttyACM0 -P 14 -p CFG-MSG,240,3,1 # GSV
ubxtool -f /dev/ttyACM0 -P 14 -p CFG-PRT,3,0,0,0,0,0,0 # ensure USB outputs NMEA
# The following command seemed to make no difference.
# If enabled systemctl will show errors but that is to be expected
# gpsctl -s -f /dev/ttyACM0
- nano /home/pi/setup-gps.sh
- Make it executable
- chmod +x /home/pi/setup-gps.sh
- Create a systemd Service (e.g., /etc/systemd/system/gps-init.service)
- sudo nano /etc/systemd/system/gps-init.service
[Unit] Description=Configure u-blox GPS at Boot After=multi-user.target Before=gpsd.service Wants=gpsd.service [Service] ExecStart=/home/pi/setup-gps.sh Type=oneshot RemainAfterExit=true [Install] WantedBy=multi-user.target
- sudo nano /etc/systemd/system/gps-init.service
- Enable the Service
- sudo systemctl daemon-reexec
- sudo systemctl enable gps-init.service
- Reboot to ensure all changes take effect
- sudo reboot now
NOTES
Your USB Dongle may be appear as device other than /dev/ttyACM0. Running the command dmesg | grep tty or ls /dev/tty* tip will allow you to verify if your GPS is appearing as /dev/ttyACM0 or another device path.
Some of the commands used to troubleshoot were the following.
- Disabling gpsd so it will not become active between reboots.
- sudo systemctl disable gpsd.socket
- sudo systemctl disable gpsd
- sudo systemctl mask gpsd.socket
- sudo systemctl mask gpsd
- Run one of the following sets of commands
- sudo systemctl stop gpsd.socket
- sudo systemctl stop gpsd
— or — - sudo reboot now
- Reenabling gpsd once done troubleshooting.
- sudo systemctl unmask gpsd.socket
- sudo systemctl unmask gpsd
- sudo systemctl enable gpsd.socket
- sudo systemctl enable gpsd
- Run one of the following sets of commands
- sudo systemctl start gpsd.socket
- sudo systemctl start gpsd
- or
- sudo reboot now
- Checking if the GPS is sending NEMA messages.
First disable gpsd
Run one of the following commands- cat /dev/ttyACM0
- cat < /dev/ttyACM0
- stty -F /dev/ttyACM0 9600
- With either command, you should see GPS NEMA messages being streamed to the output. If the command immediately returns with no output, then the GPS is not sending messages, which is a problem.
- View USB Devices
- lsusb
- Sample output
pi@PhotoBooth1:~/TouchSelfie $ lsusb Bus 001 Device 007: ID 1546:01a7 U-Blox AG [u-blox 7] Bus 001 Device 004: ID 090c:1000 Silicon Motion, Inc. - Taiwan (formerly Feiya Technology Corp.) Flash Drive Bus 001 Device 005: ID 2010:7638 USBKey Chip USBKey Module Bus 001 Device 006: ID 0424:7800 Microchip Technology, Inc. (formerly SMSC) Bus 001 Device 003: ID 0424:2514 Microchip Technology, Inc. (formerly SMSC) USB 2.0 Hub Bus 001 Device 002: ID 0424:2514 Microchip Technology, Inc. (formerly SMSC) USB 2.0 Hub Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub pi@PhotoBooth1:~/TouchSelfie $
- Sample output
- lsusb
- View the last 20 debug messages
- dmesg | tail -n 20
- Sample output
This is a capture after the fix was applied.pi@PhotoBooth1:~/TouchSelfie $ dmesg | tail -n 20
[ 25.607372] HCSPLT @0xFFFFFFC080F905C4 : 0x8001C183
[ 25.607382] HCINT @0xFFFFFFC080F905C8 : 0x00000000
[ 25.607393] HCINTMSK @0xFFFFFFC080F905CC : 0x00000000
[ 25.607403] HCTSIZ @0xFFFFFFC080F905D0 : 0x00080008
[ 25.607414] HCDMA @0xFFFFFFC080F905D4 : 0xC6718080
[ 25.607424] Host Channel 7 Specific Registers
[ 25.607432] HCCHAR @0xFFFFFFC080F905E0 : 0x01409808
[ 25.607443] HCSPLT @0xFFFFFFC080F905E4 : 0x8001C183
[ 25.607453] HCINT @0xFFFFFFC080F905E8 : 0x00000000
[ 25.607463] HCINTMSK @0xFFFFFFC080F905EC : 0x00000000
[ 25.607473] HCTSIZ @0xFFFFFFC080F905F0 : 0x00080008
[ 25.607483] HCDMA @0xFFFFFFC080F905F4 : 0xC6718080
[ 25.607598] WARN::dwc_otg_handle_mode_mismatch_intr:67: Mode Mismatch Interrupt: currently in Host mode
[ 26.641294] cdc_acm 1-1.3:1.0: ttyACM0: USB ACM device
[ 57.963631] pps_ldisc: PPS line discipline registered
[ 117.664194] WARN::dwc_otg_hcd_handle_hc_fsm:2441: Unexpected IRQ state on FSM transaction:dev_addr=7 ep=2 fsm=7, hcint=0x00000022
pi@PhotoBooth1:~/TouchSelfie $ - If there are several WARN messages such as below, then you may be having the same issue with the USB dongle not working unless it is unplugged and reinserted.
The output below is before the issue was resolved and includes unplugging and plugging in the USB GPS dongle.pi@PhotoBooth1:~ $ dmesg | tail -n 20
[ 39.437463] WARN::dwc_otg_hcd_urb_dequeue:639: Timed out waiting for FSM NP transfer to complete on 6
[ 39.437954] WARN::dwc_otg_hcd_urb_dequeue:639: Timed out waiting for FSM NP transfer to complete on 5
[ 39.438512] WARN::dwc_otg_hcd_urb_dequeue:639: Timed out waiting for FSM NP transfer to complete on 0
[ 39.439038] WARN::dwc_otg_hcd_urb_dequeue:639: Timed out waiting for FSM NP transfer to complete on 3
[ 111.617441] WARN::dwc_otg_hcd_urb_dequeue:639: Timed out waiting for FSM NP transfer to complete on 5
[ 111.617895] WARN::dwc_otg_hcd_urb_dequeue:639: Timed out waiting for FSM NP transfer to complete on 6
[ 111.618337] WARN::dwc_otg_hcd_urb_dequeue:639: Timed out waiting for FSM NP transfer to complete on 1
[ 138.125231] usb 1-1.3: USB disconnect, device number 6
[ 142.162832] usb 1-1.3: new full-speed USB device number 7 using dwc_otg
[ 142.253315] usb 1-1.3: New USB device found, idVendor=1546, idProduct=01a7, bcdDevice= 1.00
[ 142.253362] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 142.253379] usb 1-1.3: Product: u-blox 7 - GPS/GNSS Receiver
[ 142.253393] usb 1-1.3: Manufacturer: u-blox AG - www.u-blox.com
[ 142.255827] cdc_acm 1-1.3:1.0: ttyACM0: USB ACM device
pi@PhotoBooth1:~ $ - Check the status of the gps-init service we created.
- sudo systemctl status gps-init.service
- Sample output
The error, “Failed to start gps-init.service – Configure u-blox GPS at Boot.” may be ignored as it is expected when the line “gpsctl -s -f /dev/ttyACM0” is not commented out in /home/pi/setup-gps.sh.pi@PhotoBooth1:~/TouchSelfie $ sudo systemctl status gps-init.service
× gps-init.service - Configure u-blox GPS at Boot
Loaded: loaded (/etc/systemd/system/gps-init.service; enabled; preset: enabled)
Active: failed (Result: exit-code) since Sun 2025-06-29 14:21:24 EDT; 39min ago
Process: 904 ExecStart=/home/pi/setup-gps.sh (code=exited, status=1/FAILURE)
Main PID: 904 (code=exited, status=1/FAILURE)
CPU: 15.794s
Jun 29 14:21:14 PhotoBooth1 setup-gps.sh[1378]: inProtoMask (UBX NMEA RTCM2)
Jun 29 14:21:14 PhotoBooth1 setup-gps.sh[1378]: outProtoMask (UBX NMEA)
Jun 29 14:21:14 PhotoBooth1 setup-gps.sh[1378]: UBX-ACK-ACK:
Jun 29 14:21:14 PhotoBooth1 setup-gps.sh[1378]: ACK to Class x06 (CFG) ID x00 (PRT)
Jun 29 14:21:24 PhotoBooth1 setup-gps.sh[1383]: gpsctl:ERROR: timed out after 8 seconds
Jun 29 14:21:24 PhotoBooth1 setup-gps.sh[1383]: gpsctl:ERROR: no DEVICES response received.
Jun 29 14:21:24 PhotoBooth1 systemd[1]: gps-init.service: Main process exited, code=exited, status=1/FAILURE
Jun 29 14:21:24 PhotoBooth1 systemd[1]: gps-init.service: Failed with result 'exit-code'.
Jun 29 14:21:24 PhotoBooth1 systemd[1]: Failed to start gps-init.service - Configure u-blox GPS at Boot.
Jun 29 14:21:24 PhotoBooth1 systemd[1]: gps-init.service: Consumed 15.794s CPU time.
pi@PhotoBooth1:~/TouchSelfie $
- Sample output
- dmesg | tail -n 20
- Once cgps is showing that gpsd is working properly, telnet may be used to view the messages being sent by gpsd.
- If telnet is not installed, install telnet with the following command.
- sudo apt install telnet
- telnet localhost 2947
- Sample output
pi@PhotoBooth1:~/TouchSelfie $ telnet localhost 2947 Trying ::1... Connected to localhost. Escape character is '^]'. {"class":"VERSION","release":"3.22","rev":"3.22","proto_major":3,"proto_minor":14} - Issue the following command to view polling output.
- ?POLL;
- Issue the following command to see JSON output.
- ?WATCH={“enable”:true,”json”:true}
- Press <Ctrl>+] then type “quit” to exit the telnet session.
- Sample output
- If telnet is not installed, install telnet with the following command.
- CAUTION: I did notice one time that the location reported by gpsd was off by 1,000 miles to the NW. Not certain what happened but I could not replicate it. I had let cgps run for about 10 minutes to see if gpsd would update with the correct location, but it did not.
- Some other useful commands to see what is happening with USB and GPS on boot.
- journalctl | grep -i gps
- journalctl | grep -i usb
- Additional commands to monitor GPS output while gpsd is running.
- gpspipe -r
- gpsmon
