Raspberry Pi stratum 0 NTP server + PTP server

If you think having your own stratum 0 NTP server is not cool enough, why not have a PTP server at home?

Well, it looks cool, but the PTP part is currently not working!

TL ; DR

HW

Raspberry Pi CM5 (CM5102016 - 2GB RAM, 16 GB eMMC, Wifi)
- The SYNC input for the PTP is only available on CM4 and CM5 (i.e. not available on the RPi 4 and 5).
- N.B. Wifi is not necessary, but this will become my router in the near future
Mainboard: SupTronics X1501
- Dual ethernet, did I already tell this board will become my router?
GPS: Waveshare MAX-M8Q GNSS HAT for Raspberry Pi
- Because it has a PPS output
- Can be replaced by the NEO-M8T HAT, which is especially designed for timing applications, but is 3.5x more expensive.
Battery: ML1220 to store settings on the NEO-M8T HAT
Case: SupTronics X15-C1
Passive cooler: SC1752
PSU: USB-C (27W recommended by SupTronics)

I may have ordered the hardware too fast, the CM5 needs kernel > 6.12 info from here, and OpenWRT ships with kernel 6.6…

So, the PTP functionality will be tested using ubuntu 25.10 sever

SW - OS and basic settings

OpenWRT 24.10.5 setup.

It may be possible to use rpiboot to flash the eMMC as a USB mass device, but since I can’t find any documentation on the mainboard manufacturer’s site, I used a USB drive to flash the OpenWRT image on /dev/mmcblk0. And since rpi-eeprom-config does not work on OpenWRT, I used Raspberry Pi OS Lite on the USB drive.

Write the Raspberry Pi OS Lite image on the USB drive, and boot on it. If you don’t have an official power supply, you may need usb_max_current_enable=1 in your config.txt.

Configure BOOT_ORDER (see the doc).

The factory settings is 0xf2461 (SD (eMMC) -> NVMe -> USB -> Network). Since the eMMC is soldered (not removable like a SD card), the there is no way to boot on something else, once it is configured.

So let’s configure BOOT_ORDER to USB -> NVMe -> SD.

  # Configure BOOT_ORDER to USB -> NVMe -> SD and disable other factory settings
  cat <<EOF >boot.conf
  [all]
  BOOT_UART=0
  POWER_OFF_ON_HALT=0

  # USB -> NVMe -> SD
  BOOT_ORDER=0xf164
  EOF

  sudo rpi-eeprom-config --apply boot.conf

  sudo reboot # Rebooting in the same OS is necessary to write the eeprom

Now install OpenWRT on the eMMC

I find the squashfs more stable than the ext4 one, and will cause less wear on the flash. Feel free to use another image.

 # download OpenWRT
 wget https://downloads.openwrt.org/releases/24.10.5/targets/bcm27xx/bcm2712/openwrt-24.10.5-bcm27xx-bcm2712-rpi-5-squashfs-factory.img.gz

 # verify the dowload
 echo "a3356a692ccc4e22896b9fb57a001d949f7c967d924c534732272fa1745bb00d  openwrt-24.10.5-bcm27xx-bcm2712-rpi-5-squashfs-factory.img.gz" | shasum -c -

 # flash it
 zcat openwrt-24.10.5-bcm27xx-bcm2712-rpi-5-squashfs-factory.img.gz | sudo dd bs=4M of=/dev/mmcblk0


 # edit eMMC/boot/config.txt and eMMC/boot/cmdline.txt
 mkdir /tmp/boot
 sudo mount /dev/mmcblk0p1 /tmp/boot/ -o noatime

 # config.txt setup
 cat <<EOF | sudo tee -a /tmp/boot/config.txt
 [all]
 dtparam=pciex1                # for X1501 ssd
 dtoverlay=pps-gpio,gpiopin=18 # PPS on GPIO 18
 dtparam=uart0=on              # enable /dev/ttyAMA0 for the GPS
 dtparam=watchdog=off          # disable watchdog
 usb_max_current_enable=1
 EOF

 # The GNSS will need the serial port, so don't put a console on it
 sudo sed -i 's/ .*115200//' /tmp/boot/cmdline.txt
 sudo umount /tmp/boot

Remove the USB drive and reboot OpenWRT on the eMMC

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

Since this machine is not a router :

/etc/init.d/firewall disable
/etc/init.d/odhcpd disable
/etc/init.d/dnsmasq disable
reboot

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-ptp
uci set system.@system[0].timezone='CET-1CEST,M3.5.0,M10.5.0/3'
uci set system.@system[0].zonename='Europe/Zurich'
uci commit
echo pim-ptp > /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
/etc/init.d/ntpd disable
/etc/init.d/ntpd stop
opkg install chrony kmod-pps-gpio gpsd gpsd-clients \
nano rsync umdns coreutils-who zabbix-agentd python3-light kmod-usb-net-rtl8152
/etc/init.d/chronyd enable

SW - GPSD, chrony and PPS

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 chronyd for using country specific servers in /etc/config/chrony:

config pool
        option hostname '0.ch.pool.ntp.org'
        option iburst 'yes'
config systemclock 'systemclock'
...

Add the GNSS and PPS sources at the end of : /etc/chrony/chrony.conf
```
...
refclock SHM 0 refid GNSS precision 1e-1 offset 0.044 poll 0 filter 8
refclock PPS /dev/pps0 refid PPS lock GNSS poll 2 trust
```
0.044 didn’t fall out of the sky, this is the “Offset field” from the GPS given by chronyc sourcestats (with offset set at 0.00 in chrony.conf) . This time is the time necessary for the GPS data to be transmitted and decoded.

(Re-) Start chronyd

# Restarting network after chrony configuration will get the NTP servers
# from the DHCP server
/etc/init.d/network restart
/etc/init.d/chronyd restart

Check GPS and PPS functionality :

chronyc sources

MS Name/IP address         Stratum Poll Reach LastRx Last sample               
===============================================================================
#- GNSS                         0   2   377     6    +43ms[  +43ms] +/-  100ms
#* PPS                          0   1   377     2   -343ns[ -716ns] +/- 2600ns
^- redacted1.example.com        1   6   377    22  -3130us[-3128us] +/-   10ms
^- redacted2.example.com        1   6   377    22  -3188us[-3187us] +/- 7391us
^- redacted3.example.com        2   6   377    21  -5598us[-5597us] +/-   18ms
^- redacted4.example.com        2   6   377    20  -3383us[-3382us] +/-   36ms
^- router.lan                   2   6   377    15  -3231us[-3231us] +/-   41ms
^- pim-ntp.lan                  1   6   377    14    -12us[  -12us] +/-  290us
^? pim-ptp.lan                  0   8   377     -     +0ns[   +0ns] +/-    0ns

Configure NTP pool DNS and DHCP on a OpenWRT router

Setup all your NTP servers in a DNS pool (/etc/config/dhc)

...
config domain
    option name 'ntp'
    option ip 'XXX.XXX.XXX.XXX' # address of the router with a NTP server

config domain
    option name 'ntp'
    option ip 'XXX.XXX.XXX.YYY' # address of the ntp server (from our older post)

config domain
    option name 'ntp'
    option ip 'XXX.XXX.XXX.YYY' # address of the ntp+ptp server (from this post)
...

Setup the DHCP to announce NTP servers:

uci add_list dhcp.lan.dhcp_option='42,XXX.XXX.XXX.XXX,XXX.XXX.XXX.YYY,XXX.XXX.XXX.ZZZ'
uci commit

Restart dnsmasq
```
/etc/init.d/dnsmasq restart
```

(Optional) Optimisation for timing

The backup battery on the Waveshare MAX-M8Q GNSS HAT is mandatory. Whitout it, the module will lose it’s configuration every power loss. The symptom will be NO FIX, since the module will go back to 9600 bauds.

set jumpers on A
connect to your favorite Linux host using the USB cable

start gpsd on the usb port

 ubxtool -s 9600 -S 115200
 ubxtool -p MODEL,2
 ubxtool -p CFG-PMS,0
 ubxtool -p SAVE
 ubxtool -p COLDBOOT # validate the settings are OK

re-set jumpers on B
configure 11500 bauds using -s 115200 in /etc/init.d/gpsd: ```bash … [ “$enabled” = “0” ] && return 1

procd_open_instance procd_set_param command “$PROG” -N -n -s 115200 [ “$listen_globally” -ne 0 ] && procd_append_param command -G procd_append_param command -S “$port”

  ...
  ```

ptp (using ubuntu server 25.10)

the PTP server does not work at this time

The complete install will be documented once the required drivers reach OpenWRT.

In brief:

install ubuntu server 25.10
add the config.txt lines into /boot/firmware/config.txt
remove the serial console from /boot/firmware/current/cmdline.txt.
reboot

install and configure gpsd (in /etc/default/gpsd)

 # Devices gpsd should collect to at boot time.
 # They need to be read/writeable, either by user gpsd or the group dialout.
 DEVICES="/dev/ttyAMA0"

 # Other options you want to pass to gpsd
 GPSD_OPTIONS="-n -s 115200"

 # Automatically hot add/remove USB GPS devices via gpsdctl
 USBAUTO="true"

install and configure chrony

sudo rm /etc/chrony/sources.d/ubuntu-ntp-pools.sources
echo "pool 0.ch.pool.ntp.org iburst" | sudo tee /etc/chrony/sources.d/pim.sources
echo "pool ntp.lan iburst" | sudo tee -a /etc/chrony/sources.d/pim.sources
echo "refclock SHM 0 refid GNSS precision 1e-1 offset 0.044 poll 0 filter 8" | sudo tee /etc/chrony/conf.d/pim.conf
echo "refclock PPS /dev/pps0 refid PPS lock GNSS poll 2 trust" | sudo tee -a /etc/chrony/conf.d/pim.conf
sudo systemctl restart chrony

connect GNSS module PPS pin (GPIO8 or dedicated output) to Ethernet_SYNC_OUT (J2 pin 6)

configure Ethernet_SYNC_OUT as a PPS input

 # Configure the pin as input, 1 means input, 0 is the ptp channel 0 (from ethtool -T eth0 | grep 'Hardware timestamp provider index:')
 echo 1 0 | sudo tee /sys/class/ptp/ptp0/pins/SYNC_OUT

 # Enable timestamping (0 is the ptp channel number and 1 is enable
 echo 0 1 | sudo tee /sys/class/ptp/ptp0/extts_enable

 # should display 1 timestamp per second
 # disconnect the cable and the timestamps will stop

 while true; do cat /sys/class/ptp/ptp0/fifo ; done

configure ptp timemaster

 sudo apt install linuxptp
 sudo systemctl disable timemaster.service

Sync PTP hardware clock to PPS

 # we don't use nmea for time of day (gpsd uses the gps data), so sync
 # PTP with the system clock. TAI is 37 seonds ahead of TAI
 sudo phc_ctl eth0 "set;" adj 37 # fixme get it from leap-seconds.list
 # ubuntu is not up to date
 sudo wget -P /etc/linuxptp https://data.iana.org/time-zones/tzdb-2026a/leap-seconds.list
 cat <<EOF | sudo tee -a /etc/linuxptp/ts2phc.conf
 [global]
 leapfile /etc/linuxptp/leap-seconds.list
 step_threshold 0.1
 ts2phc.tod_source generic
 logging_level 7

 [eth0]
 ts2phc.pin_index 0
 EOF

 ts2phc -f /etc/linuxptp/ts2phc.conf -m -q -l 7

Sync chrony with the the PTP hardware clock

 echo "refclock SHM 0 refid GNSS precision 1e-1 offset 0.044 poll 0 filter 8" | sudo tee /etc/chrony/conf.d/pim.conf
 echo "refclock PPS /dev/pps0 refid PPS lock GNSS poll 2" | sudo tee -a /etc/chrony/conf.d/pim.conf
 echo "refclock SHM 2 refid PPSp tai lock GNSS poll 2" | sudo tee -a /etc/chrony/conf.d/pim.conf
 sudo systemctl restart chrony

 # -M2 -> write to SHM 2
 # offset is zero, since it is configured as TAI in chrony
 phc2sys -s eth0 -E ntpshm -O 0 -M 2

ptp master work in progress

At this time ptp4l --serverOnly 1 -i eth0 -l 7 --tx_timestamp_timeout 500 fails with this error:

timed out while polling for tx timestamp
increasing tx_timestamp_timeout or increasing kworker priority may correct this issue, but a driver bug likely causes it
port 1 (eth0): send sync failed
port 1 (eth0): MASTER to FAULTY on FAULT_DETECTED (FT_UNSPECIFIED)

~~~

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