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From https://en.wikipedia.org/wiki/Network_Time_Protocol, "Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks." Practically, it allows you to have current time/date on your APF even if your don't have an RTC (you will need an Internet connection or a GPS ;-)).

Get current Time from Internet

# ntpd -nqp

Time synchronisation from GPS

Buildroot Debian
  • You will need the "real" NTP daemon, not the Busybox one.
root@opos6ul:~# apt-get install ntp
  • Edit/Replace config file (/etc/ntp.conf) with:
# Allow only time queries, at a limited rate, sending KoD when in excess.
# Allow all local queries (IPv4, IPv6)
restrict default nomodify nopeer noquery limited kod
restrict [::1]

server mode 17 minpoll 4 maxpoll 4 prefer
fudge flag3 1 flag2 0 flag1 1 time1 0.0

  • means: "use /dev/gps0 and parse it as NMEA to get time" (See [1]).
  • mode 17 is for 9600 bauds GPS providing GPRMC frames
  • To create /dev/gpsX (here GPS is connected to UART2):
# ln -sf /dev/ttymxc1 /dev/gps0
  • You can add the previous in ntpd start script (/etc/init.d/ntp):
--- /etc/init.d/ntp
+++ /etc/init.d/ntp
@@ -59,6 +59,7 @@
                        exit 1
+               ln -sf /dev/ttymxc1 /dev/gps0
                start-stop-daemon --start --quiet --oknodo --pidfile $PIDFILE ---startas $DAEMON -- -p $PIDFILE $NTPD_OPTS
  • To launch ntpd (if not automatically launched at startup):
# /usr/sbin/ntpd -g -c /etc/ntp.conf