This README describes necessary steps to build and install RT_PREEMPT Linux kernel for the Raspberry Pi4 board. RT Kernel is a part of the ROS2 real-time system setup. Raspberry Pi4 is a reference board used by the ROS 2 real-time community for the development. RT Kernel is configured as described in Kernel configuration section. Kernel is built automatically by the Github action, and the artifacts are located under the build stable. Please follow installation instructions to deploy a new kernel to the RPI4 board.
Ubuntu raspi kernel is modified to produce an RT Linux kernel. Ubuntu is a ROS 2 Tier 1 platform and Ubuntu kernel was selected to align to it. It is possible to build the raspi kernel for both Ubuntu LTS releases 20.04 and 22.04.
RT Kernel is configured using configuration parameters from the file. In the case you need to build your own kernel read the description below.
Go to the Action tab, find the Build stable, go inside the latest workflow run, download, and unzip artifacts called RPI4 RT Kernel deb packages. This archive contains three debian packages. Follow instructions to deploy them on the RPI4.
Go to the Developer settings and generate a token to access the repo via Github API. Use this token in conjunction with your Github name to retrieve build artifacts.
$ token=<my_token>
# rertieve all artifacts
$ curl -i -u <my github name>:$token -H "Accept: application/vnd.github.v3+json" https://api.github.com/repos/ros-realtime/linux-real-time-kernel-builder/actions/artifacts | grep archive_download_url
"archive_download_url": "https://api.github.com/repos/ros-realtime/linux-real-time-kernel-builder/actions/artifacts/91829081/zip",
"archive_download_url": "https://api.github.com/repos/ros-realtime/linux-real-time-kernel-builder/actions/artifacts/91534731/zip",
# download the latest one
$ curl -u <my github name>:$token -L -H "Accept: application/vnd.github.v3+json" https://api.github.com/repos/ros-realtime/linux-real-time-kernel-builder/actions/artifacts/91829081/zip --output rpi4_rt_kernel.zip
$ unzip rpi4_rt_kernel.zipUbuntu 20.04 x86_64 based Dockerfile is developed to cross-compile a new kernel.
Docker container comes with cross-compilation tools installed, and a ready-to-build RT Linux kernel:
- ARMv8 cross-compilation tools
- Linux source build dependencies
- Linux source
buildinfo, from where kernel config is copied - Ubuntu
raspiLinux source installed under~/linux_build - RT kernel patch downloaded and applied - the nearest to the recent
raspiUbuntu kernel
It finds the latest raspi linux-image and the closest to it RT patch. If the build arguments specified it will build a corresponding kernel version instead.
For the local build:
git clone https://github.com/ros-realtime/linux-real-time-kernel-builder
cd linux-real-time-kernel-builderdocker build [--no-cache] [--build-arg UBUNTU_VERSION=<ubuntu name>] [--build-arg KERNEL_VERSION=<kernel version>] [--build-arg UNAME_R=<raspi release>] [--build-arg RT_PATCH=<RT patch>] [--build-arg LTTNG_VERSION=<LTTNG version>] -t rtwg-image .where:
<ubuntu name>isjammyorfocal, default isjammy<kernel version>is5.15.0or5.4.0, default is5.15.0<raspi release>is in a form of5.15.0-1023-raspi, see Ubuntu raspi Linux kernels<RT patch>is in a form of5.15.76-rt53, see RT patches<LTTNG version>is2.13, default is2.13
docker run -t -i rtwg-image bashThere is a separate kernel configuration fragment.config-fragment introduced to apply ROS2 real-time specific kernel settings. Below is an example:
$ cat .config-fragment
CONFIG_PREEMPT_RT=y
CONFIG_NO_HZ_FULL=y
CONFIG_HZ_1000=y
# CONFIG_AUFS_FS is not setIf you need to reconfigure it, run
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfigAlternatively, you can modify .config-fragment and then merge your changes in the .config by running
cd $HOME/linux_build/linux-raspi
ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- ./scripts/kconfig/merge_config.sh .config $HOME/linux_build/.config-fragmentcd $HOME/linux_build/linux-raspi
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- LOCALVERSION=-raspi -j `nproc` bindeb-pkgYou need 16GB free disk space to build it, it takes a while, and the results are located:
raspi:~/linux_build/linux-raspi $ ls -la ../*.deb
-rw-r--r-- 1 user user 8123580 Jan 16 16:34 ../linux-headers-5.15.74-rt53-raspi_5.15.74-rt53-raspi-1_arm64.deb
-rw-r--r-- 1 user user 58802024 Jan 16 16:34 ../linux-image-5.15.74-rt53-raspi_5.15.74-rt53-raspi-1_arm64.deb
-rw-r--r-- 1 user user 1185420 Jan 16 16:34 ../linux-libc-dev_5.15.74-rt53-raspi-1_arm64.debFollow these links to download and install Ubuntu 22.04 on your Raspberry Pi4
- Install Ubuntu on a Raspberry Pi
- Download Ubuntu Raspberry Pi server image
- Create an Ubuntu image for a Raspberry Pi on Ubuntu
# initial username and password
ubuntu/ubuntuAfter that you need to connect to the Internet and update your system
$ sudo apt-get update && apt-get upgradeOptionally you can install a desktop version
$ sudo apt-get update && apt-get upgrade && apt-get install ubuntu-desktopAssumed you have already copied all *.deb kernel packages to your $HOME directory
cd $HOME
sudo dpkg -i linux-image-*.deb
sudo rebootAfter reboot you should see a new RT kernel installed and real-time enabled
ubuntu@ubuntu:~$ uname -a
Linux ubuntu 5.15.74-rt53-raspi #1 SMP PREEMPT_RT Mon Jan 16 14:10:16 UTC 2023 aarch64 aarch64 aarch64 GNU/Linux
ubuntu@ubuntu:~$ cat /sys/kernel/realtime
1To build x86_64 Linux kernel, see Building Realtime rt_preempt kernel for ROS 2
LTTng stands for Linux Trace Toolkit: next generation and is an open source toolkit that enables low-level kernel tracing which can be extremely useful when calculating callback times, memory usage and many other key characteristics.
As this repository is within the ros-realtime organization it can be assumed that most users will install ROS 2 on the end system - which then they can use ros2_tracing to trace various things. Since ros2_tracing uses LTTng as its tracer, and since the lttng-modules package is not easily available for the raspberry-pi RT linux kernel we build it into the kernel here as a work around.