Raspberry Pi 5 PCIe HAT with I225 NIC and GNSS Support

The Raspberry Pi 5 PCIe HAT is designed to bring precision timing and advanced network functionality to the Raspberry Pi 5 platform. Leveraging the PCIe interface via an FPC connection, this HAT expands the Pi’s capabilities by integrating a high-performance I225 2.5G Ethernet NIC, precise timing inputs and outputs via SMA connectors, and a GNSS module slot for global time synchronization. It’s a powerful tool for building small form-factor PTP (Precision Time Protocol) clients or even grandmasters, ideal for time-sensitive networking applications.

Included in box

A. TimeHAT

B. 40 pin spacer

C. 16-pin FPC PCIe cable

Key Features:

I225 2.5G Ethernet NIC

The HAT features an Intel I225 NIC connected to the Raspberry Pi 5 over the PCIe interface, delivering fast, reliable 2.5G Ethernet connectivity. This makes it suitable for applications requiring high-speed networking combined with precise timing.

2.5G Ethernet: Take full advantage of the I225’s support for faster Ethernet speeds, perfect for data-intensive and time-critical applications.

Precision Timing via SMA Ports

The HAT includes two SMA connectors for timing signal input and output:

SMA Input (SDP1 on I225): Allows the HAT to receive a 1PPS (one pulse per second) signal, which can be used as a reference to discipline the NIC’s internal clock.

SMA Output (SDP0 on I225): Provides a 1PPS output signal from the NIC, which can be used to measure precise time intervals or synchronize external equipment.

Spare U.FL (SDP3 on I225): A raw unbuffered connection from SDP3 on the I225 goes to a spare U.FL, can be used as input or output.

These timing features enable the HAT to act as either a PTP client or a PTP grandmaster, providing precise time synchronization for your network.

OCP M.2 GNSS Slot (2242 Form Factor)

The HAT includes an M.2 slot designed for OCP-compliant GNSS modules, allowing you to add GNSS functionality to your Raspberry Pi setup:

UART Connection: The GNSS module communicates with the Pi via the standard Pi HAT header.

1PPS from GNSS to SDP2 on I225: The 1PPS signal from the GNSS module connects directly to the NIC, allowing the NIC to discipline itself to GPS time. This feature is essential for building a reliable grandmaster clock, providing accurate time sourced directly from satellites.

Optional TCXO and DCTCXO Upgrade

For enhanced timing stability, the HAT supports an upgrade to a high-precision Temperature-Compensated Crystal Oscillator (TCXO). For even more advanced use cases, a Digitally Controlled TCXO (DCTCXO) can be installed, allowing software control over the clock frequency:

Improved Holdover Performance: The TCXO ensures that the NIC’s timing remains stable even during GNSS signal loss.

Digital Tuning: The DCTCXO upgrade allows for digital adjustments to the NIC’s PTP clock, making it easier to maintain precision over time.

Applications

This HAT is designed for a variety of precision timing and networking applications:

PTP Client or Grandmaster: Use the HAT to synchronize your network devices with sub-microsecond accuracy.

GNSS Disciplined Clock: Leverage the GNSS module to create a highly accurate, satellite-synchronized clock.

1PPS Signal Measurement: Measure and verify 1PPS signals for precise timekeeping in your system.

Edge Networking: Deploy the HAT in edge computing environments where precise timing is crucial.

Why This HAT is Special

The Raspberry Pi 5 PCIe HAT combines high-speed networking with advanced timing features in a compact, easy-to-deploy form factor. It allows makers, hobbyists, and professionals to build small yet powerful PTP solutions using the versatile Raspberry Pi 5 ecosystem. The HAT's ability to act as both a PTP client and a grandmaster, combined with GNSS support and optional TCXO upgrades, makes it a unique offering in the world of precision timing hardware.

What This Enables

Home Labs: Create a PTP grandmaster for your home lab with ease.

IoT Gateways: Build precise IoT gateways that require synchronized time across devices.

Research and Development: Ideal for experimenting with PTP, GNSS, and timing protocols in various network configurations.

Whether you’re building a precise timekeeping device or exploring the world of networked time protocols, the Raspberry Pi 5 PCIe HAT is your gateway to advanced timing applications. Designed to integrate seamlessly with the Raspberry Pi 5, this HAT empowers you to bring professional-grade timing and networking to your projects.

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Usage steps

Pre-setup steps

A. Install linuxptp

sudo apt install linuxptp

B. Download testptp

cd ~ ; mkdir testptp; cd testptp

wget https://raw.githubusercontent.com/torvalds/linux/refs/heads/master/tools/testing/selftests/ptp/testptp.c

wget https://raw.githubusercontent.com/torvalds/linux/refs/heads/master/include/uapi/linux/ptp_clock.h

sudo cp ptp_clock.h /usr/include/linux/ptp_clock.h

C. Compile testptp

gcc -Wall -lrt testptp.c -o testptp

D. Install testptp

sudo cp testptp /usr/bin/

E. Verify testptp works

sudo testptp -d /dev/ptp0 -l

Should see

pi@raspberrypi:~/testptp $ sudo testptp -d /dev/ptp0 -l

name SDP0 index 0 func 0 chan 0

name SDP1 index 1 func 0 chan 0

name SDP2 index 2 func 0 chan 0

name SDP3 index 3 func 0 chan 0

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Configure 1PPS Output

1. Setup SDP0 (SMA1, closest to HAT header) as periodic output

sudo testptp -d /dev/ptp0 -L0,2

sudo testptp -d /dev/ptp0 -p 1000000000

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Read 1PPS SMA Input

A. Setup SDP1 (SMA2 , furthest from HAT header) as timestamp input

sudo testptp -d /dev/ptp0 -L1,1

B. Read timestamps, use -1 to read forever and ctrl+C to stop, using 5 here as demo. Note: I225 driver passes both edges to Linux, so both rising and falling edges will be listed. A fix for this is listed below, requires patching and building kernel

sudo testptp -d /dev/ptp0 -e 5

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Discipline to 1PPS SMA Input

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Access GNSS UART

A. Enable UART, but not serial console for Raspberry Pi. Use raspi-config, 3. Interface Options -> I6 Serial port.

sudo raspi-config

Login shell -> No Serial port hardware -> Yes Finish

reboot

B. Once rebooted, you'll need to link GNSS UART to a ttySX name for tools to use it

sudo ln -s /dev/ttyAMA0 /dev/ttyS10

C. Simple serial check using tio, use ctrl+t q to quit

tio -b 38400 /dev/ttyS10

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Use gpsd / cgps to see GPS status

A. Install gpsd and cgps

sudo apt-get install gpsd gpsd-clients

B. Configure gpsd to point to /dev/ttyAMA0 , the GNSS UART

sudo vim /etc/default/gpsd

C. Add /dev/ttyAMA0 to GPSD_OPTIONS, and set baud rate

GPSD_OPTIONS="/dev/ttyAMA0 -s 38400"

D. Enable gpsd on startup

sudo systemctl enable gpsd

E. Start gpsd now

sudo systemctl start gpsd

F. Use cgps to see the GPS status, use ctrl+c to exit

sudo cgps

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Use pygpsclient to see GPS status (requires monitor)

A. Install pygpsclient, https://github.com/semuconsulting/PyGPSClient?tab=readme-ov-file#installation

python3 -m pip install --upgrade pygpsclient

B. Once installed, run it with pygpsclient in terminal

pygpsclient

C. Select /dev/ttyS10 as serial port, set baud rate as 38400, then click USB/UART button.

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Discipline to 1PPS from GNSS module

a. To have this work properly, you'll need to install the PPS in fix below

A. Install GPS and make sure it's locked properly. You should also see a blinking LED on the M.2 module if 1PPS is being generated.

B. Enable PPS input on GNSS -> I226 SDP2 pin

sudo testptp -d /dev/ptp0 -L 2,1

C. Set NIC PHC based on system time to get Time-Of-Day

sudo phc_ctl eth1 "set;" adj 37

D. Use ts2phc to discipline NIC from 1PPS

sudo ts2phc -c /dev/ptp0 -s generic --ts2phc.pin_index 2 -m -l 7

E. TODO: Figure out how to get NMEA stream direct from GPS to work with ts2phc or into NIC PHC

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Fix 1PPS input to only use rising edge (Advanced)

A. Build the kernel, https://www.raspberrypi.com/documentation/computers/linux_kernel.html , commands below as of 1-10-2025

cd ~ ; mkdir kernel; cd kernel

sudo apt install git

git clone --depth=1 https://github.com/raspberrypi/linux

sudo apt install bc bison flex libssl-dev make

cd linux ; KERNEL=kernel_2712 ; make bcm2712_defconfig;

make -j6 Image.gz modules dtbs

sudo make -j6 modules_install

sudo cp /boot/firmware/$KERNEL.img /boot/firmware/$KERNEL-backup.img

sudo cp arch/arm64/boot/Image.gz /boot/firmware/$KERNEL.img

sudo cp arch/arm64/boot/dts/broadcom/*.dtb /boot/firmware/

sudo cp arch/arm64/boot/dts/overlays/*.dtb* /boot/firmware/overlays/

sudo cp arch/arm64/boot/dts/overlays/README /boot/firmware/overlays/

B. Reboot and make sure kernel is installed from your build, as the steps list

C. Apply patch from TAP github. Run below commands to apply the patch and rebuild

cd ~ ; cd kernel ; cd linux

wget https://raw.githubusercontent.com/opencomputeproject/Time-Appliance-Project/refs/heads/master/Incubation/Software/I225_ppsin_fix/i225_pps_rising_edge_only_1-31-2025.patch

patch -p1 < i225_pps_rising_edge_only_1-31-2025.patch

KERNEL=kernel_2712 ; make bcm2712_defconfig;

make -j6 Image.gz modules dtbs

sudo make -j6 modules_install

sudo cp /boot/firmware/$KERNEL.img /boot/firmware/$KERNEL-backup.img

sudo cp arch/arm64/boot/Image.gz /boot/firmware/$KERNEL.img

sudo cp arch/arm64/boot/dts/broadcom/*.dtb /boot/firmware/

sudo cp arch/arm64/boot/dts/overlays/*.dtb* /boot/firmware/overlays/

sudo cp arch/arm64/boot/dts/overlays/README /boot/firmware/overlays/

D. reboot and now testptp / ts2phc / any use of 1pps input on I225 will only use rising edge