A Raspberry Pi stratum 1 time server.
Takes in GPS (or potentially other stratum 0 time sources), spits out NTP, PTP, etc.
To run a decent time server (with high accuracy), you need a few things:
- A computer running Linux (all the nice tooling for network time is availabe here)
- A high quality time source (GPS is most commonly used these days)
- A network adapter capable of hardware timestamping (Intel and ASIX make some good NICs for time-related applications)
There are many options for each of the above items—for example, many use Adafruit's Ultimate GPS HAT or its USB equivalent for GPS acquisition, and for PTP, you can use a Compute Module 4 or 5's built-in NIC (with PPS in or out), or add on a compatible NIC on the Pi 5 with something like the uPCIty Lite.
My own hardware configuration—which is the basis for the code in this repository, consists of:
- Computer: Raspberry Pi 5 model B
- Time source: u-blox ZED-F9T-00B-01 (installed on TimeHAT V4)
- NIC: Intel i226-LM (installed on TimeHAT V4)
A precise GPS signal for nanosecond-accurate time requires a decent antenna with as clear a view of the sky as possible. Some GPS receivers are better than others, but even USB receivers will do better than NTP!
I use a small active GPS antenna for testing, but for permanent installation it is best to mount a higher-quality GPS antenna outside, clear of obstructions.
Make sure you have Ansible installed. Copy the following example files and customize them according to your setup:
example.hosts.initohosts.iniexample.config.ymltoconfig.yml
Because I can't quite get cmdline.txt changes automated the way I like, manually edit /boot/firmware/cmdline.txt and remove the portion console=serial0,115200, so GPS can use the serial port.
Now run the Ansible playbook:
ansible-playbook main.yml
This playbook will configure:
- GPSd: interface with the u-blox GPS and provide GPS data to other applications
- Chrony: NTP server, which also sync GPS time (with Internet NTP server backup) to the system clock
- Linux PTP: synchronize the system clock to the NIC PHC (Physical Hardware Clock), and set up the Pi as a PTP grandmaster clock
Intel i226 Notes: Currently I can't get the i226 to work with DHCP at all, so I have to manually set an IP address using
nmtui. It also doesn't work at 2.5 Gbps currently, and it can't be overridden via Linux, so I make sure to plug it into a 1 Gbps port on my network.
Some handy commands:
# GPS-related debugging
sudo systemctl status gpsd # check gpsd status
gpsmon -n # monitors gpsd output
cgps -s # also monitors gps output
# PTP timestamping debugging
ethtool -T eth0 # or eth1, lists hardware clock info
# Chrony debugging
chronyc sources -v # shows sources with documentation of fields
chronyc -n tracking # shows detailed timing data
# Check on NTP service from another computer
ntpdate -q [ip of grandmaster]
# Check on PTP clocks and offsets (assuming ptp4l is running)
wget https://tsn.readthedocs.io/_downloads/f329e8dec804247b1dbb5835bd949e6f/check_clocks.c
gcc -o check_clocks check_clocks.c
sudo ./check_clocks -d eth0 # or eth1 (the interface you're using for PTP)
Much of the work that went into this project was documented in this thread on the TimeHat v2.
For PTP, you need to install and configure PTP for Linux on slave/client machines, and synchronize them to the master/server node as well.
An example configuration for a slave/client node is set up in ptp-client-node.yml, and further examples may be provided in the future.
GPLv3 or Later
Jeff Geerling, with assistance from Ahmad Byagowi and Oleg Obleukhov from Meta.
