shkwon98/rpi4-preemptrt

To build real-time kernel 4.19.86 with preempt-rt for Raspberry Pi 4.

Raspberry Pi 4 Preempt-RT Patch

These steps will help you through the installation of preempt-rt on the Raspberry Pi 4. The kernel that is used is the 4.19.86 linux kernel.

• It contains additional support as an option to use W5500 Ethernet network driver for users who need extra ethernet port on raspberry pi.
• You can find out much more simplified method using pre-built kernel on the link

Requirements:

• Raspberry Pi 4
• 16gb Micro-SD card + reader
• Computer with Ubuntu
• (Option) WIZnet W5500 Ethernet chip with SPI interface

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. Create directories on the host computer

host@ubuntu:~$ mkdir rpi-kernel
host@ubuntu:~$ cd rpi-kernel
host@ubuntu:~/rpi-kernel$ mkdir rt-kernel

2. Start by pulling the linux repository

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

B. Building linux

1. Environment variable setting

host@ubuntu:~/rpi-kernel$ export ARCH=arm
host@ubuntu:~/rpi-kernel$ export CROSS_COMPILE=~/rpi-kernel/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-
host@ubuntu:~/rpi-kernel$ export INSTALL_MOD_PATH=~/rpi-kernel/rt-kernel
host@ubuntu:~/rpi-kernel$ export INSTALL_DTBS_PATH=~/rpi-kernel/rt-kernel

2. Setting for Raspberry pi 4

host@ubuntu:~/rpi-kernel$ export KERNEL=kernel7l
host@ubuntu:~/rpi-kernel$ cd linux/
host@ubuntu:~/rpi-kernel/linux$ make bcm2711_defconfig

3. Configurate Kernel Compile options

host@ubuntu:~/rpi-kernel/linux$ sudo apt-get install libncurses-dev libssl-dev flex bison
host@ubuntu:~/rpi-kernel/linux$ make menuconfig

4. Edit the following variables:

[Kernel hacking] → [Debug preemptible kernel] Off
(Option) [Device Drivers] → [Network device support] → [Ethernet driver support] → [WIZnet W5100 Ethernet support], [WIZnetW5100/W5200/W5500 Ethernet support for SPI mode] On

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

host@ubuntu:~/rpi-kernel/linux$ make -j4 zImage modules dtbs
host@ubuntu:~/rpi-kernel/linux$ make –j4 modules_install dtbs_install

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

1. Create .img Kernel file

host@ubuntu:~/rpi-kernel/linux$ mkdir $INSTALL_MOD_PATH/boot
host@ubuntu:~/rpi-kernel/linux$ ./scripts/mkknlimg ./arch/arm/boot/zImage $INSTALL_MOD_PATH/boot/$KERNEL.img

2. Replace the Kernel to Raspberry Pi

host@ubuntu:~/rpi-kernel/linux$ cd $INSTALL_MOD_PATH
host@ubuntu:~/rpi-kernel/rt-kernel$ tar czf ../rt-kernel.tgz *
host@ubuntu:~/rpi-kernel/rt-kernel$ cd ..
host@ubuntu:~/rpi-kernel$ scp rt-kernel.tgz pi@<raspberry pi IP address>:/tmp

D. Installing the preempt-rt on the Raspberry pi

1. Inside the raspberry pi, unpack the .tgz and copy it

pi@raspberrypi:~$ cd /tmp
pi@raspberrypi:/tmp$ tar xzf rt-kernel.tgz
pi@raspberrypi:/tmp$ cd boot
pi@raspberrypi:/tmp/boot$ sudo cp -rd * /boot/
pi@raspberrypi:/tmp/boot$ cd ../lib
pi@raspberrypi:/tmp/lib$ sudo cp -rd * /lib/
pi@raspberrypi:/tmp/lib$ cd ../overlays
pi@raspberrypi:/tmp/overlays$ sudo cp -d * /boot/overlays
pi@raspberrypi:/tmp/overlays$ cd ..
pi@raspberrypi:/tmp$ sudo cp -d bcm* /boot/

2. Edit the boot configutarion

pi@raspberrypi:/tmp$ sudo nano /boot/config.txt

Add in the beginning:

kernel=kernel7l.img

(Option) Type in the last line:

dtoverlay=w5500

3. Reboot and check the patched kernel

pi@raspberrypi:/tmp$ sudo reboot
pi@raspberrypi:~$ uname -r

BENCHMARK:

• cyclictest benchmark

rpi4-preemptrt's Issues

Issue after Build the linux kernel

After doing

make -j4 zImage 
make -j4 modules 
make -j4 dtbs 

I get error at this step do you have idea what could be the issue
make -j4 modules_install

I have attached the error snapshot