The Raspberry Pi Compute Module 4 (CM4) has taken the maker and developer community by storm with its versatility, compact form factor, and powerful performance. While the CM4 is widely used for everything from industrial automation to IoT projects, one of its often-overlooked but essential capabilities is clock synchronisation.
In applications where precise timekeeping is vital—such as network monitoring, data logging, and real-time systems—accurate clock sync is crucial. This blog will explore how the Raspberry Pi CM4 handles clock synchronisation, why it’s important, and the tools and protocols available to achieve accurate time on your CM4-based projects.
Why Clock Synchronisation Matters
Accurate timekeeping is essential in a variety of applications:
Network Management: In systems where data is exchanged across multiple nodes or servers, synchronised clocks ensure that timestamps are consistent, making it easier to monitor performance, detect errors, and maintain logs.
IoT Devices: In IoT environments, devices must coordinate their activities and communicate with minimal latency. Clock synchronisation ensures that devices remain aligned, especially in scenarios that require real-time interaction.
Data Logging: Whether you're capturing sensor data, monitoring environmental conditions, or keeping logs of system events, accurately timestamping data is vital for consistency and reliability.
Financial Transactions: In industries such as finance, precise time synchronisation helps maintain order in high-frequency trading environments and ensures that transaction records are accurate.
The Raspberry Pi CM4 can be used in all of these scenarios, and more, thanks to its ability to synchronise its clock using network protocols and external hardware.
Built-In Clock Capabilities of the Raspberry Pi CM4
By default, the Raspberry Pi CM4, like other Raspberry Pi models, doesn't have a built-in Real-Time Clock (RTC). This means that after a reboot or power cycle, the system loses track of time until it can synchronise with an external time source.
However, the CM4 supports clock synchronisation using the following methods:
1. Network Time Protocol (NTP)
The most common method of synchronising the CM4’s clock is via Network Time Protocol (NTP). NTP is a widely-used protocol that enables devices to synchronise their clocks over a network, ensuring consistency across systems.
How NTP Works on the Raspberry Pi CM4:
The CM4 connects to an NTP server (such as public NTP servers or a local time server within your network).
The server provides time information based on a reliable time source (like an atomic clock).
The CM4 adjusts its system clock based on the NTP server’s data, ensuring accurate and reliable timekeeping.
Benefits of Using NTP:
Simple to set up: NTP is built into most Linux distributions, including Raspberry Pi OS, making it easy to configure and use.
Sufficient accuracy: For most general applications, NTP provides millisecond-level accuracy, which is suitable for IoT devices, web servers, and many data logging applications.
To set up NTP on the CM4:
Install NTP using the command:
sudo apt-get install ntpEdit the configuration file (/etc/ntp.conf) to include preferred NTP servers.
Restart the service:
sudo systemctl restart ntp2. Real-Time Clock (RTC) Module Integration
For applications that require the Raspberry Pi CM4 to maintain time during power outages or disconnections from a network, you can add an external RTC module. These modules are inexpensive and allow the CM4 to keep track of time even when powered off.
Why Use an RTC Module?
Offline timekeeping: Unlike NTP, an RTC continues to function without internet access, ensuring the Pi keeps accurate time even during reboots or offline operations.
Battery-backed: RTC modules typically have a small battery that keeps the clock running when the CM4 is powered off.
How to Set Up an RTC on the CM4:
Connect an RTC module (e.g., DS3231 or DS1307) to the CM4 via I2C.
Install necessary drivers:
sudo apt-get install i2c-toolsDetect the RTC module by running:
sudo i2cdetect -y 1Configure the RTC to be the system clock source:
Add the following line to /boot/config.txt:
dtoverlay=i2c-rtc,ds3231Disable fake-hwclock:
sudo apt-get -y remove fake-hwclock
sudo update-rc.d -f fake-hwclock removeReboot the system, and the CM4 will now use the RTC to maintain accurate time.
3. Precision Time Protocol (PTP)
For use cases that require extremely precise time synchronisation—down to the microsecond or even nanosecond range—the Precision Time Protocol (PTP) is the ideal solution. While not natively supported on most Raspberry Pi boards without additional hardware, PTP can be implemented with specific external adapters.
Why Use PTP?
High accuracy: PTP can synchronize clocks with an accuracy of up to nanoseconds, making it ideal for applications like high-frequency trading, telecommunications, and industrial automation.
Hardware-assisted synchronisation: PTP works best with hardware that supports timestamping at the network interface level.
Setting up PTP on the CM4 generally involves connecting it to PTP-capable network hardware or using an external PTP Grandmaster Clock to distribute time signals across your network.
Advanced Clock Synchronisation Techniques for the Raspberry Pi CM4
If your application requires higher levels of precision, there are additional methods for fine-tuning the clock synchronisation capabilities of the CM4:
1. GPS Time Synchronisation
The CM4 can also synchronise time via GPS modules, which provide an extremely accurate and independent time source. GPS-based time synchronisation is useful for remote IoT systems where network access may be limited or unavailable.
Setting Up GPS Time Sync:
Connect a GPS module to the CM4 .
Install GPS time-sync software such as Timebeat and configure it to provide time data.
Synchronise the system clock with the GPS signal using Timebeat with GPS as the time source.
2. Timebeat: An NTP Alternative for Precision Sync
While NTP is the standard for network-based time synchronisation, Chrony is a popular alternative offering better performance in environments with unstable network connections. Timebeat can more quickly adjust to clock drift and is especially useful for devices that spend a lot of time offline.
To install Timebeat on the Raspberry Pi CM4:
Run the command:
sudo apt-get install timebeat-*Configure Timebeat in /etc/timebeat/timebeat.yml and specify your NTP servers or GPS source.
Start the service:
sudo systemctl start timebeatTimebeat offers improved synchronisation in dynamic environments and is often a preferred choice for IoT and industrial applications.
Conclusion: Optimising Clock Synchronisation on the Raspberry Pi CM4
The Raspberry Pi CM4’s flexibility and performance make it an excellent choice for projects that require accurate and reliable time synchronisation. Whether you’re using NTP for standard network-based synchronisation, integrating an RTC module for offline operations, or leveraging PTP and GPS for highly precise timekeeping, the CM4 is fully capable of meeting your time sync needs.
For most general applications, NTP offers a simple and effective solution. However, for more complex systems—particularly in industries like telecommunications, industrial automation, or data centers—the use of RTC modules, GPS sync, or PTP can provide the required level of precision.
By understanding and implementing the right clock synchronisation methods, you can ensure that your CM4-based projects remain perfectly in sync, regardless of network conditions or environmental challenges.