FreeBSD 14 USB VK‐162 - BYO-NTP/recipes GitHub Wiki

date server os gnss daemon 🎯 🗣️
2025-05 Raspberry Pi 4
Raspberry Pi 5
Chuwi Larkbox X		 FreeBSD
14		 Stratux VK-162
u-blox 7		 chrony
NTPsec
ntp		 3 ms
3 ms
7 ms		 discuss
discuss
discuss

1. Install OS

Install instructions for Pi 4, Pi 5, Chuwi Larkbox

2. Program the VK-162

Connect the USB plug to a Windows computer that has u-blox u-center installed. Configure per the recommendations on the gnss page.

3. Configure USB

When a USB device is plugged in, FreeBSD emits a couple lines of text to the console and dmesg:

dmesg | grep -i gps
ugen1.6: <u-blox AG - www.u-blox.com u-blox 7 - GPS/GNSS Receiver> at usbus1
umodem0: <u-blox AG - www.u-blox.com u-blox 7 - GPS/GNSS Receiver, class 2/0, rev 1.10/1.00, addr 5> on usbus1

That output tells us the device was attached with the umodem driver so we can read the docs for umodem and determine that the USB device was attached at /dev/cuaU*.

ls /dev/cuaU*

And there we find cuaU0!

/dev/cuaU0      /dev/cuaU0.init /dev/cuaU0.lock

The NTP daemons look to /dev/gps0 by default, so link gps0 to the serial port using devfs:

test -L /dev/gps0 && rm /dev/gps0
grep -q gps0 /etc/devfs.conf && sed -i '' -e 's/^link.*gps0$//g' /etc/devfs.conf
echo 'link    cuaU0 gps0' >> /etc/devfs.conf
service devfs restart

4. Install a NTP daemon

Each section heading is a link with many more details about installing, configuring, and verifying that particular NTP daemon.

chrony

export NTP_REFCLOCKS=$(cat <<EO_CHRONY
refclock SHM 0 refid NMEA offset 0.054 precision 0.04 poll 4 trust
EO_CHRONY
)
curl -sS https://byo-ntp.github.io/tools/chrony/install.sh | sh

Note: on the pi4, I needed offset -0.009

NTPsec

When used with USB connected GNSS, the gpsd driver typically increases precision by a decimal place, so it's the default here:

export NTP_REFCLOCKS=$(cat <<EO_NTPSEC
refclock gpsd minpoll 1 maxpoll 3 time2 0.05 mode 2 prefer
#refclock nmea minpoll 3 maxpoll 4 time2 0.05 baud 115200 mode 8 prefer
EO_NTPSEC
)
curl -sS https://byo-ntp.github.io/tools/ntpsec/install.sh | sh

ntp

export NTP_REFCLOCKS=$(cat <<EO_NTP_NMEA
server 127.127.20.0 minpoll 3 maxpoll 4 mode 88 prefer
fudge 127.127.20.0 refid NMEA time2 0.048 minjitter 0.05
EO_NTP_NMEA
)
curl -sS https://byo-ntp.github.io/tools/ntp/install.sh | sh

Alternatively, using ntp's GPSD-NG driver with gpsd:

export NTP_REFCLOCKS=$(cat <<EO_NTP_GPSD
server 127.127.46.0 minpoll 3 maxpoll 4 mode 0 prefer
fudge 127.127.46.0 refid NMEA time2 0.05 minjitter 0.05
EO_NTP_GPSD
)
curl -sS https://byo-ntp.github.io/tools/ntp/install.sh | sh
gpsd_devices="/dev/cuaU0"
service gpsd restart
service ntpd restart

Observe

  • watch the status in near real time (requires installing gnu-watch):
    • printf '\e[8;9;80t'; ssh -t pi5 gnu-watch -n2 chronyc sources
    • printf '\e[8;9;80t'; ssh -t pi5 gnu-watch -n2 ntpq -c peer
  • Measure the offset
  • Gather statistics with telegraf + influxdb + grafana or similar.

References

Performance

chrony

NTPsec

ntp

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