Pi OS 12 VK‐162 - BYO-NTP/recipes GitHub Wiki

Instructions for Pi 4 or Pi 5

Connect the VK-162 to a USB port of a Windows computer with u-blox u-center installed. Configure per the recommendations on the gnss page.

Then plug the USB plug into your NTP server.

The VK-162 presents itself to the system via the cdc_acm driver, so look for that:

dmesg | grep cdc_acm | grep tty

[    4.708559] cdc_acm 1-1.1:1.0: ttyACM0: USB ACM device

And there is the GPS unit, at ttyACM0. If it presents at another location, like ttyACM1, adjust the following commands accordingly.

• symlink /dev/ttyACM0 to /dev/gps0
• configure the USB serial port for low latency

apt install -y setserial
/bin/setserial /dev/ttyACM0 low_latency
cat > /etc/udev/rules.d/10-gps.rules <<EOL
KERNEL=="ttyACM0", SYMLINK+="gps0", GROUP="dialout", MODE="0660"
KERNEL=="ttyACM0", RUN+="/bin/setserial /dev/ttyACM0 low_latency"
EOL

udevadm control --reload-rules
udevadm trigger

Exports a refclock config and then installs (if needed) and configures the NTP daemon.

export NTP_REFCLOCKS=$(cat <<EO_CHRONY
refclock SHM 0 refid NMEA offset 0.05
EO_CHRONY
)
curl -sS https://byo-ntp.github.io/tools/chrony/install.sh | sh

export NTP_REFCLOCKS=$(cat <<EO_NTPSEC
refclock nmea minpoll 3 maxpoll 4 time2 0.052 mode 8 baud 115200
EO_NTPSEC
)
curl -sS https://byo-ntp.github.io/tools/ntpsec/install.sh | sh

The gpsd driver would improve accuracy here, but it's not built into the apt package.

export NTP_REFCLOCKS=$(cat <<EO_NTP
server 127.127.20.0 minpoll 3 maxpoll 4 mode 88
fudge 127.127.20.0 refid NMEA time2 0.052 minjitter 0.1
EO_NTP
)
curl -sS https://byo-ntp.github.io/tools/ntp/install.sh | sh

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

• GNSS
• NTP daemons
• Linux CDC ACM

chrony

NTPsec

ntp