Raspberry Pi 4 Xenomai 3 Patch

These steps will help you through the installation of xenomai on the Raspberry Pi 4. The kernel that is used is the 4.19.86 linux kernel.
Patches from Tantham-h are used to help the installation and make the USB work through the PCIE-bus that is added in the Raspberry Pi 4.

Requirements:

• Raspberry Pi 4
• 16gb Micro-SD card + reader
• Computer with Ubuntu
• Wifi/LAN connection

Create a new raspbian image on the micro-SDcard with the Pi imager. Use the file on the link below.
2020-02-13-raspbian-buster.zip

A. Directory initialization

1. Start by pulling the linux repository on the host computer.

host@ubuntu:~$ git clone -b rpi-4.19.y https://github.com/raspberrypi/linux.git linux-rpi-4.19.86-xeno3

2. Create a linked folder for easy access.

host@ubuntu:~$ ln -s linux-rpi-4.19.86-xeno3 linux

3. Download the xenomai tar.bz2 and extract it. Also create a linked folder for the xenomai installation.

host@ubuntu:~$ wget https://xenomai.org/downloads/xenomai/stable/xenomai-3.1.tar.bz2
host@ubuntu:~$ tar -xjvf xenomai-3.1.tar.bz2
host@ubuntu:~$ ln -s xenomai-3.1 xenomai

Modify 'xenomai/scripts/prepare-kernel.sh' file
Replace 'ln -sf' by 'cp' so that it will copy all neccessary xenomai files to linux source

4. Download the patches into xeno3-patches

host@ubuntu:~$ mkdir xeno3-patches && cd xeno3-patches
host@ubuntu:~/xeno3-patches$ wget https://github.com/shkwon98/rpi4-xenomai3/blob/main/ipipe-core-4.19.82-arm-6-mod-4.49.86.patch
host@ubuntu:~/xeno3-patches$ wget https://github.com/shkwon98/rpi4-xenomai3/blob/main/pre-rpi4-4.19.86-xenomai3-simplerobot.patch
host@ubuntu:~/xeno3-patches$ cd ..

B. Patching linux with xenomai

1. Patch linux with the pre-patch from Tantham-h (If the patch returns with error, just ignore)

host@ubuntu:~$ cd linux
host@ubuntu:~/linux$ patch -p1 <../xeno3-patches/pre-rpi4-4.19.86-xenomai3-simplerobot.patch

2. Patch linux with xenomai

host@ubuntu:~/linux$ ../xenomai/scripts/prepare-kernel.sh --linux=./ --arch=arm --ipipe=../xeno3-patches/ipipe-core-4.19.82-arm-6-mod-4.49.86.patch

C. Building linux

1. Preparation on host PC

host@ubuntu:~$ sudo apt-get install gcc-arm-linux-gnueabihf
host@ubuntu:~$ sudo apt-get install --no-install-recommends ncurses-dev bc

2. Get the default config of the BCM2711 into the linux directory

host@ubuntu:~/linux$ make -j4 O=build ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bcm2711_defconfig

3. Set the menuconfig to the right settings

host@ubuntu:~/linux$ make -j4 O=build ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig

4. Edit the following variables:

Kernel features —> Timer frequency 1000Hz
General setup —> (-v7l-xeno3) Local version - append to kernel release
CPU powermanagement –> CPU Frequency scaling –> [] CPU Frequency scaling
MemoryManagament options —> [] Allow for memory compaction
Kernel hacking —> [] KDGB: kernel debugger
Xenomai/cobalt —> Drivers —> Real-time GPIO drivers —> [*] GPIO controller
Xenomai/cobalt —> Drivers —> Real-time IPC drivers –> [*] RTIPC protocol familty

5. Build the linux kernel (This can take some time, so get coffee or tea...)

host@ubuntu:~/linux$ make -j4 O=build ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bzImage modules dtbs

D. Installing the linux kernel on the Micro-SD card

1. Create a shortcut to the identifier for the PI4 ARM version of the kernel

host@ubuntu:~/linux$ KERNEL=kernel7l

2. In terminal, locate the fresh installed SD card and see which mounts points are created

host@ubuntu:~/linux$ lsblk

Now we assume that sdb1 being the FAT (boot) partition, and sdb2 being the ext4 filesystem (root) partition.

3. Create mount points for both these partitions and mount the sd card to them.

host@ubuntu:~/linux$ mkdir mnt
host@ubuntu:~/linux$ mkdir mnt/fat32
host@ubuntu:~/linux$ mkdir mnt/ext4
host@ubuntu:~/linux$ sudo mount /dev/sdb1 mnt/fat32
host@ubuntu:~/linux$ sudo mount /dev/sdb2 mnt/ext4

4. Install the modules of the build linux system and install them on the root partition.

host@ubuntu:~/linux$ sudo env PATH=$PATH make O=build ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- INSTALL_MOD_PATH=mnt/ext4 modules_install

5. Install the kernel image, bts packets and the overlays into the boot partition.
   Also the original kernel image is saved, in the case that the kernel does not boot.

host@ubuntu:~/linux$ sudo cp mnt/fat32/$KERNEL.img mnt/fat32/$KERNEL-backup.img
host@ubuntu:~/linux$ sudo cp build/arch/arm/boot/zImage mnt/fat32/$KERNEL.img
host@ubuntu:~/linux$ sudo cp build/arch/arm/boot/dts/*.dtb mnt/fat32/
host@ubuntu:~/linux$ sudo cp build/arch/arm/boot/dts/overlays/*.dtb* mnt/fat32/overlays/

6. Edit the neccessary boot configs and cmdline such that the pi can boot, also add the ssh access file

host@ubuntu:~/linux$ touch mnt/fat32/ssh
host@ubuntu:~/linux$ sudo nano mnt/fat32/cmdline.txt

Add at the end of the first line:

dwc_otg.fiq_enable=0 dwc_otg.fiq_fsm_enable=0 dwc_otg.nak_holdoff=0 isolcpus=0,1 xenomai.supported_cpus=0x3

host@ubuntu:~/linux$ sudo nano mnt/fat32/config.txt

Add in the beginning:

total_mem=3072

7. Unmount the SD card and insert it into the Raspberry pi and power it up with the ethernet cable attached to the host computer.

host@ubuntu:~/linux$sudo umount mnt/fat32
host@ubuntu:~/linux$sudo umount mnt/ext4

8. Boot the raspberry pi and ssh into it, check the linux kernel.

pi@raspberrypi:~$ uname -r

E. Installing the xenomai libraries on the Raspberry pi

1. Build the xenomai libraries on the host PC.

host@ubuntu:~$ cd xenomai
host@ubuntu:~/xenomai$ ./scripts/bootstrap
host@ubuntu:~/xenomai$ ./configure --host=arm-linux-gnueabihf --enable-smp --with-core=cobalt
host@ubuntu:~/xenomai$ make
host@ubuntu:~/xenomai$ sudo make install
host@ubuntu:~/xenomai$ tar -cjvf rpi4-xeno3-deploy.tar.bz2 /usr/xenomai

2. Copy the constructed tar.bz2 file to your raspberry pi.

host@ubuntu:~/xenomai$ scp rpi4-xeno3-deploy.tar.bz2 pi@<raspberry pi IP address>

3. Switch to the raspberry pi (SSH into the raspberry pi)

host@ubuntu:~/xenomai$ ssh pi@<raspberry pi IP address>:/home/pi

4. Inside the raspberry pi, unpack the tar.bz2 and copy it to /usr

pi@raspberrypi:~$ sudo tar -xjvf rpi4-xeno3-deploy.tar.bz2 -C /

5. Create a config file and add the xenomai libraries to it.

pi@raspberrypi:~$ sudo nano /etc/ld.so.conf.d/xenomai.conf

Add to this file:

#xenomai lib path
/usr/local/lib
/usr/xenomai/lib

6. Load the config and reboot.

pi@raspberrypi:~$ sudo ldconfig
pi@raspberrypi:~$ sudo reboot

7. Run some tests and you are done!

pi@raspberrypi:~$ sudo /usr/xenomai/bin/xeno-test
pi@raspberrypi:~$ sudo /usr/xenomai/bin/latency

If latency tool get start and show some result, you are now have realtime kernel for your rpi