Holybro Pixhawk RPI CM4 Baseboard
Last updated
Last updated
The Holybro Pixhawk RPi CM4 Baseboard is a single-board solution that pre-integrates a (swappable) Pixhawk flight controller with the Raspberry Pi CM4 companion computer ("RPi"). The baseboard has a compact form factor with all the connections needed for development.
The flight controller module is internally connected to RPi CM4 through TELEM2, but may alternatively be connected using Ethernet with the provided external cable.
This baseboard is plug-in compatible with Holybro Pixhawk 5X, Holybro Pixhawk 6X, and any other Pixhawk controller that follows the Pixhawk Autopilot Bus Standard guidelines for mechanical compatibility across vendors.
:::note The board follows the Pixhawk Connector Standard and Pixhawk Autopilot Bus Standard (including the guidelines for "mechanical compatibility across vendors"). :::
Holybro Pixhawk RPi CM4 Baseboard (www.holybro.com)
The baseboard can be purchased with or without an RPi CM4 and/or flight controller:
The Raspberry Pi CM4 (CM4008032) supplied by Holybro has the following specification:
RAM: 8GB
eMMC: 32GB
Wireless: No
The recommended minimum specification for the RPi CM4 is:
RAM: 4GB (or 8GB)
eMMC: 16GB
Wireless: Yes
:::note The Holybro Documentation has more detailed (and possibly more "up to date") port and connection information. :::
The diagram below shows all the connectors and ports on the baseboard.
The flight controller TELEM2 port is internally connected to RPi CM4 as shown:
GPIO14
TXD
GPIO15
RXD
GPIO16
CTS
GPIO17
RTS
:::note The connection must be also be configured in both RPi and PX4 (unless Ethernet is used instead). :::
A plug-compatible flight controller such as Holybro Pixhawk 5X and Holybro Pixhawk 6X can simply be pushed into the module slot.
Flight controllers that have a different form factor will need additional wiring.
This section shows how to install/attach a Raspberry Pi CM4 to the baseboard.
To install the Raspberry Pi CM4 companion computer:
Disconnect the FAN wiring.
Remove these 4 screws on the back side of the baseboard.
Remove the baseboard case, install the CM4, and use the 4 screws to attach it (as shown):
Reattach the cover.
The PM03D power module is supplied with the board.
The RPi CM4 and flight controller must be powered separately:
The flight controller is powered via the CLIK-Mate cable to POWER1 or POWER2 port
The RPi CM4 is powered by the USB C (CM4 Slave) connection. You can also use your own power supply to power the RPi CM4 baseboard.
The image below shows the wiring in greater detail.
This section explains how you install your preferred Linux distro, such as "Raspberry Pi OS 64bit" onto the RPi EMCC.
Notes:
If you are using PX4, you will need to use PX4 version 1.13.1 or newer for PX4 to recognize this baseboard.
The fan does not indicate if the RPi CM4 is powered/running or not.
The power module plugged into Power1/2 does not power the RPi part. You can use the additional USB-C Cable from the PM03D power module to the CM4 Slave USB-C port.
The Micro-HDMI port is an output port.
RPi CM4 boards that do not have Wifi device will not connect automatically. In this case you will need to plug it into a router or plug a compatible Wifi dongle into the CM4 Host ports.
To flash a RPi image onto EMMC.
Switch Dip-Switch to RPI.
Connect computer to USB-C CM4 Slave port used to power & flash the RPi.
Get usbboot, build it and run it.
You can now install your preferred Linux distro using The rpi-imager. Make sure you add WiFi and SSH settings (hidden behind the gear/advanced symbol).
Once done, unplugging USB-C CM4 Slave (this will unmount the volumes, and power off the CM4).
Switch Dip-Switch back to EMMC.
Power on CM4 by providing power to USB-C CM4 Slave port.
To check if it’s booting/working you can either:
Check there is HDMI output
Connect via SSH (if set up in rpi-imager, and WiFi is available).
:::note If you are using Ethernet to connect the FC and RPi, this setup is not needed. :::
The Pixhawk FC module is internally connected to the RPi CM4 using TELEM2 (/dev/ttyS4). The FC and RPi CM4 must both be configured to communicate over this port.
The FC should be set up to connect to the TELEM2 port correctly by default. If not, you can configure the port using the parameters as shown.
To enable this MAVLink instance on the FC:
Connect a computer running QGroundControl via USB Type C port on the baseboard labeled FC
MAV_1_CONFIG = 102
MAV_1_MODE = 2
SER_TEL2_BAUD = 921600
Reboot the FC.
On the RPi side:
Connect to the RPi (using WiFi, a router, or a Wifi Dongle).
Enable the RPi serial port by running RPi-config
Go to 3 Interface Options, then I6 Serial Port. Then choose:
login shell accessible over serial → No
serial port hardware enabled → Yes
Finish, and reboot. (This will add enable_uart=1 to /boot/config.txt, and remove console=serial0,115200 from /boot/cmdline.txt
Now MAVLink traffic should be available on /dev/serial0 at a baudrate of 921600.
Make sure the CM4 is connected to the internet, e.g. using a wifi, or ethernet.
Install MAVSDK Python:
Copy an example from the MAVSDK-Python examples.
Change the system_address="udp://:14540" to system_address="serial:///dev/serial0:921600"
Try out the example. Permission for the serial port should already be available through the dialout group.
The flight controller module is internally connected to RPi CM4 from TELEM2 (Serial).
You can also set up a local Ethernet connection between them using the supplied cable. Ethernet connectivity provides a fast, reliable, and flexible communication alternative to using USB or other serial connections.
:::note For more general information see: PX4 Ethernet Setup. :::
To set up a local ethernet connection between CM4 and the flight computer, the two ethernet ports need to be connected using the provided 8 pin to 4 pin connector.
The pinout of the cable is:
A
B
B
A
C
D
D
C
| N/A
| N/A
| N/A
| N/A
Since there is no DHCP server active in this configuration, the IP addresses have to be set manually:
First, connect to the CM4 via SSH by connecting to the CM4’s WiFi (or use a Wifi dongle). Once the ethernet cables are plugged in, the eth0 network interface seems to switch from DOWN to UP.
You can check the status using:
You can also try to enable it manually:
It then seems to automatically set a link-local address, for this example it looks like this:
This means the CM4’s ethernet IP is 169.254.21.183.
Now connect to the NuttX shell (using a console, or the MAVLink shell), and check the status of the link:
For this example, it is DOWN at first.
To set it to UP:
Now check the config again:
However, it doesn’t have an IP yet. Set one that is similar to the one on the RPi CM4:
Then check it:
Now the devices should be able to ping each other.
Note that this configuration is ephemeral and will be lost after a reboot, so we’ll need to find a way to configure it statically.
First from the CM4:
Then from the flight controller in NuttShell:
For this, we need to set the MAVLink instance to send traffic to the CM4's IP address:
For an initial test we can do:
This will send MAVLink traffic on UDP to port 14540 (the MAVSDK/MAVROS port) to that IP which means MAVSDK can just listen to any UDP arriving at that default port.
To run a MAVSDK example, install mavsdk via pip, and try out an example from MAVSDK-Python/examples.
For instance:
Get The Pixhawk Raspberry Pi CM4 Baseboard By Holybro Talking With PX4 (px4.io blog):
Tutorial showing how to connect Pixhawk 6X + Raspberry Pi on CM4 baseboard via wired Ethernet.
