Real-Time Kernel for RaspberryPi 2

This post will describe how to compile a RT-kernel for RaspberryPi 2.

I'm using UBUNTU 14.04 LTS 64bit for compiling Raspbian Jessie.

After a long time, I needed a RT kernel for a new project with the new RaspberryPi2. Realizing My old post has broken links, I struggled again with the task. This time, after a successful attempt, I'm determined to put it all here step by step.

following:

https://github.com/emlid/linux-rt-rpi

https://www.raspberrypi.org/documentation/linux/kernel/building.md and https://www.raspberrypi.org/documentation/linux/kernel/configuring.md and http://wiki.linuxcnc.org/cgi-bin/wiki.pl?RaspbianXenomaiBuild#Post_install

##### Tested on UBUNTU 14.04 LTS with Rasbian Jessie 4.1

# install needed packages for compiling the kernel

sudo apt-get install libncurses5-dev libncursesw5-dev

#Download Raspberry Pi tools:

git clone https://github.com/raspberrypi/tools.git

# Download source files and patches

git clone -b rpi-4.1.y --depth 1 git://github.com/raspberrypi/linux.git linux-rpi-4.1.y

# Download RT patch 

wget https://www.kernel.org/pub/linux/kernel/projects/rt/4.1/patch-4.1.15-rt17.patch.xz

xz -d patch-4.1.15-rt17.patch.xz

# patch the kernel. This step might produce errors

# if rt-patch and the kernel don't match

cd linux-rpi-4.1.y

cat ../patch-4.1.15-rt17.patch | patch -p1

#Export the following variables to specify cross-compilation options:

export ARCH=arm 

#to compile on a x64-machine you need to export:

export CROSS_COMPILE=~/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-

#create a config file for Raspberry Pi 2:

make CROSS_COMPILE=${CROSS_COMPILE} ARCH=arm bcm2709_defconfig

# make changes to the config

make CROSS_COMPILE=${CROSS_COMPILE} ARCH=arm menuconfig

enable Preemption model -> Fully preemptible Kernel (RT)

change timer freq to 1000Hz

enable device tree (all options)

#Compile the kernel:

make CROSS_COMPILE=${CROSS_COMPILE} ARCH=arm -j5

#Install modules, will result in "lib" folder with modules and firmware:

mkdir kernel-rt

INSTALL_MOD_PATH=kernel-rt make CROSS_COMPILE=${CROSS_COMPILE} ARCH=arm modules_install

## Install the kernel to non-RT image:

Copy arch/arm/boot/Image to /boot/kernel7.img on SD card.

Copy arch/arm/boot/dts/bcm2709-rpi-2-b.dtb to /boot/bcm2709-rpi-2-b.dtb on SD card

# add to /boot/config.txt

echo “device_tree=bcm2709-rpi-2-b.dtb” >> /boot/config.txt

Copy (merge if necessary) kernel-rt/lib to / on SD card.

## Testing RT-Image

Insert SD card and connect RPI to power, keyboard and screen. 

Login with user pi and password raspberry

#Installing cyclictest utility on Raspberry Pi:

git clone http://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git 

cd rt-tests

make all

cp ./cyclictest /usr/bin/

cd ~

sudo cyclictest -l100000 -m -n -a0 -t1 -p99 -i400 -h400 -q

# WITH NO RT RESULT:

# Total: 000100000

# Min Latencies: 00015

# Avg Latencies: 00021

# Max Latencies: 00118

# Histogram Overflows: 00000

# Histogram Overflow at cycle number:

# Thread 0:

# WITH RT RESULT:

# Total: 000100000

# Min Latencies: 00013

# Avg Latencies: 00020

# Max Latencies: 00066

# Histogram Overflows: 00000

# Histogram Overflow at cycle number:

# Thread 0: