cross_compile

Cross-Compilation

Since the processing power of the Raspberry Pi Zero module is insufficient for a "quick" compilation, we made tools to help you compile ROS2 on your PC for the Raspberry Pi Zero. Therefore, this tutorial will give you instructions on how to use the tools to cross-compile ROS2 for Raspberry Pi Zero (could be also extended to other Raspberry Pi versions).

Prerequisites

Please make sure everything is ready for you to proceed:

• Raspberry Pi OS ready on your Raspberry Pi (tutorial).
• SSH access to Raspberry Pi (tutorial).
• Docker on your PC (tutorial).
• Optional SSH server on your PC (sudo apt install openssh-server).

Raspberry Pi Preparation

ROS2 requires the following packages to be installed on your Raspberry Pi:

sudo apt update

# Compilation dependencies
sudo apt install \
    liblog4cxx-dev \
    python3-dev

# Runtime dependencies
sudo apt install \
    python3-numpy \
    python3-netifaces \
    python3-yaml

# Optional tools
sudo apt install sshfs

ROS2 Cross-Compilation on Your PC

Now we can start a process of ROS2 cross-compilation. The supplied Docker image is equipped with most of the tools you need, so start it with:

./start_docker.sh

This command will build and run the Docker container, and allocate a pseudo-TTY. It means that you can use it as an another operating system. From now on, you will be able to do most of the tasks from the Docker container.

If you use Linux, please make sure you did the post-installation steps.

Rootfs Preparation

As your Raspberry Pi is equipped with ROS2 dependencies you have to synchronize the rootfs. This will allow the cross-compiler to use header files and libraries from your Raspberry Pi. There are two ways to get the rootfs inside your Docker.

The first way, you can synchronize the content of the rootfs:

rsync -rLR --safe-links pi@[raspberry_pi_ip]:/{lib,usr,opt/vc/lib} /home/develop/rootfs

Initially, rsync will take more time to perform synchronization, but the cross-compilation process will be faster after (as the cross-compiler doesn't have to transfer a file from Raspberry Pi every time).

The second way, you can use sshfs tool to mount the rootfs:

sshfs -o follow_symlinks,allow_other -o cache_timeout=115200 pi@[raspberry_pi_ip]:/ /home/develop/rootfs

Compilation Commands

In the Docker, we prepared a few commands with the cross-* prefix to bootstrap your development. For example, you can use cross-initialize to download the ROS2 source code or cross-colcon-build to build it. These commands are simple bash functions located in .bashrc. You can see how the commands are implemented by typing e.g. type cross-initialize and change them according to your needs. Therefore, in the Docker container type:

cross-initialize

to download the ROS2 source code. By default, it will initialize the ROS2 Foxy distribution, but if you want to change it you can use ROS_DISTRO environment variable, e.g. for ROS2 Dashing:

export ROS_DISTRO=dashing

To compile the ROS2 source code execute:

cross-colcon-build --packages-up-to ros2topic

Flag --packages-up-to ros2topic will compile ros2topic and all it's recursive dependencies. Also, note that it can happen that you need to run the command twice to compile fastrtps package.

Using the Cross-Compiled ROS2 on your Raspberry Pi

To use the cross-compiled ROS2 on your Raspberry Pi you have to copy ./ros2_ws/install to the Raspberry Pi:

scp -r install pi@[raspberry_pi_ip]:/home/pi/ros2

Once the install directory is copied you can use source /home/pi/ros2/local_setup.bash to set-up ROS2 on the Raspberry Pi.

Alternatively, you can mount it by running the following commands on the Raspberry Pi:

mkdir ros2
sshfs [pc_username]@[pc_address]:[path_to_this_folder]/ros2_ws/install ros2
source ros2/local_setup.bash

But in that case, make sure that your PC has SSH server installed and configured:

sudo apt install openssh-server
sudo systemctl start sshd

Cross-Compiling Custom ROS2 Packages

With these tools, you can compile custom ROS2 packages as well. It is enough to put the source code of the package to ./ros2_ws/src and run cross-colcon-build inside the Docker. For example, to compile the epuck_ros2 package execute the following commands:

git clone --recurse-submodules https://github.com/cyberbotics/epuck_ros2.git src/epuck_ros2
cross-colcon-build --packages-up-to epuck_ros2_driver

You can use the --packages-select epuck_ros2_driver flag to compile the epuck_ros2_driver package only.

Missing Dependencies

Sometimes, your package will depend on ROS2 packages that are not a part of the ROS2 base. In that case, you can use cross-generator to download it. For example, in case of the epuck_ros2 package, the camera_info_manager dependency is missing, so you can download it with:

cross-generator camera_info_manager