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Patching Kernel with RTAI

What is RTAI?

RTAI - the RealTime Application Interface for Linux - which lets you write applications with strict timing constraints for your favourite operating system.

First download the linux kernel source from www.kernel.org. I used the linux-2.6.24.tar.bz2 as this was tested on Ubuntu 8.04 which already comes with 2.6.24. DONOT use the kernel source from the ubuntu repository. Download RTAI 3.6.2 – rtai-3.6.2.tar.bz2 from www.rtai.org and put both files in /usr/src/

unpack this files

cd /usr/src/
sudo tar xfv linux-2.6.24.tar.bz2
sudo tar xfv rtai-3.6.2.tar.bz2

Rename linux source directory to a to identify it as a patched linux kernel

mv linux-2.6.24 linux-build-2.6.24-rtai-3.6.2

assuming that you are logged in as root, or use sudo before the command.

Create symbolic links

ln -snf linux-build-2.6.24-rtai-3.6.2 linux
ln -snf rtai-3.6.2 rtai

installed all the packages required for compiling the kernel

apt-get install build-essential kernel-package ncurses-dev

Now its time to patch the kernel source the RTAI patch

cd /usr/src/linux
patch -p1 -b < /usr/src/rtai/base/arch/x86/patches/hal-linux-2.6.24-x86-2.0-07.patch

you can also find patches for other kernels in /rtai-3.6.2/base/arch/i386/patches/

now ------------
cp /boot/config-`uname -r` ./.config
make oldconfig # then press Enter to all the prompts

• Now is time to configure the new kernel:
make menuconfig

In the menu there are many parameters you can change if you know what you are doing.
The changes needed by RTAI are:
– Enable loadable module support > Module versioning support = no
- Processor type and features > Interrupt pipeline = yes
– Processor type and features > Subarchitecture Type = PC-compatible
– Power management options > Power Management support = no
– Power management options > CPU Frequency scaling > CPU Frequency scaling= no

– General setup > Local version - append to kernel release = -rtai-3.6.2

Optionally you can make a backup for the new configuration file:
cd /usr/src/linux ; .config /boot/config-2.6.24-rtai-3.6.2

make-kpkg clean
make-kpkg --initrd kernel_image kernel_headers
cd /usr/src/
dpkg -i linux-image-2.6.24-rtai-3.6.2_2.6.24-rtai-3.6.2-10.00.Custom_i386.deb
dpkg -i linux-headers-2.6.24-rtai-3.6.2_2.6.24-rtai-3.6.2-10.00.Custom_i386.deb

Due to a bug, the next two commands need to be executed:
cd /usr/src/linux-headers-2.6.24-rtai-3.6.2/arch/x86/
cp /usr/src/linux-headers-2.6.24-19/arch/x86/Makefile_32* ./

Now its time to reboot and choose the new RTAI patched kernel in Grub

RTAI Installation

cd /usr/src/rtai
mkdir build
cd build

make -f ../makefile menuconfig
make install
cp -a /dev/rtai_shm /lib/udev/devices/
cp -a /dev/rtf[0-9] /lib/udev/devices/
echo /usr/realtime/lib/ > /etc/ld.so.conf.d/rtai.conf
ldconfig

Final Testing

If everything goes well , RTAI is properly installed. To be sure execute the latency test:
cd /usr/realtime/testsuite/kern/latency/
./run

Press Ctrl-C to stop.

Thats It.