Raspberry pi stratum 0 NTP server

HW

Raspberry Pi 3
SD card (200MB will do, yes, 200MB!)
Waveshare MAX-M8Q GNSS HAT for Raspberry Pi
Raspberry Pi official case for 3B+

SW

Download OpenWRT 24.10.5 openwrt-24.10.5-bcm27xx-bcm2710-rpi-3-squashfs-factory.img.gz, flash it on the SD card.

I find the squashfs more stable than the ext4 one, and it will cause less wear on the SD card.

Modify the /boot/config.txt (config.txt in the boot partition):

...
[all]
# Place your custom settings here.
dtoverlay=pps-gpio,gpiopin=18
...

Disable the serial console (we need the serial port for the GPS) in /boot/cmdline.txt
```
console=tty1 root=PARTUUID=c8dca970-02 rootfstype=squashfs,ext4 rootwait
```
Assemble all the HW, and boot. The raspberry will have the 192.168.1.1 address, but I prefer it to DHCP.
```
uci set network.lan.proto=dhcp
uci commit
/etc/init.d/network restart
```

Setup a root password

root@OpenWrt:~# passwd
Changing password for root
New password:
Bad password: too weak
Retype password:
passwd: password for root changed by root

Setup authorized_keys and disable root password login

Configure hostname

uci set system.@system[0].hostname=pim-ntp
uci commit
echo pim-ntp > /proc/sys/kernel/hostname

Install the tools

opkg update
uci set system.ntp.enable='0'
uci commit
/etc/init.d/sysntpd disable
/etc/init.d/sysntpd stop
opkg install ntpd ntp-utils ntpd kmod-pps-gpio gpsd gpsd-clients \
rsync nano coreutils-who zabbix-agentd python3-light
/etc/init.d/ntpd enable

Configure gpsd

uci set gpsd.core.device='/dev/ttyAMA0'
uci set gpsd.core.enabled='1'
uci commit
/etc/init.d/gpsd enable
/etc/init.d/gpsd start

Check GPS connectivity : cgps -s -u m should show Status 3D FIX

Configure ntp for using country specific servers:

uci delete system.ntp.server
uci add_list system.ntp.server='0.ch.pool.ntp.org'
uci add_list system.ntp.server='1.ch.pool.ntp.org'
uci add_list system.ntp.server='2.ch.pool.ntp.org'
uci add_list system.ntp.server='3.ch.pool.ntp.org'

Configure ntpd : /etc/ntpd.d/gps.conf

# GPS Serial data reference
server 127.127.28.0 minpoll 4 maxpoll 4
fudge 127.127.28.0 time1 0.0 refid GPS
# GPS PPS reference
server 127.127.28.1 minpoll 4 maxpoll 4 prefer
fudge 127.127.28.1 refid PPS

(Re-) Start ntpd
```
/etc/init.d/ntpd restart
```

Check GPS and PPS functionality :

root@pim-ntp:~# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
+SHM(0)          .GPS.            0 l   13   16  377    0.000   +0.117   0.537
*SHM(1)          .PPS.            0 l   12   16  377    0.000  +143.77   0.081
 ch1.ntp.ynnk.de 210.65.119.71    2 u    4   64    1   14.490  +148.66   1.090
-ntp03.maillink. .PPS.            1 u   27   64    1   18.667  +146.12   4.040
+time.hb9gun.ch  .DTS.            1 u   35   64    1   16.882  +148.64   1.001
 i7.isp.theswiss .PPS.            1 u    5   64    1   16.474  +205.98   0.983

A small animation : watch ntpq -p (opkg install procps-ng-watch)

~~~

Question, remark, bug? Don't hesitate to contact me or report a bug.