Installing a RealTime Kernel based on xenomai

1. Log in into your Raspberry PI.
2. Download the Raspberry PI Linux Kernel 3.2.21 via git
   git clone --branche=rpi-3.2.21 --depth 1 git://github.com/bootc/linux.git
3. Download xenomai 2.6.1
   wget http://download.gna.org/xenomai/stable/xenomai-2.6.1.tar.bz2
4. Download and apply the raspberry PI Xenomai Patch
   http://www.cim.mcgill.ca/~ian/rpi-linux-3.2.21-xenomai-2.6.1.patch
5. Copy your current Linux Configuration into your Linux-Kernel-Source-Tree
   zcat /proc/config.gz > /path/to/kerneltree/.config
6. Comment out some stuff in your Kernel.config, which are good for reducing the latency
   # CONFIG_NO_HZ
   # CONFIG_CC_STACKPROTECTOR
   # XENO_OPT_STATS
   Select via make menuconfig:
   Go to: "Kernel Features -> Preemption Model" and set "Preemptible Kernel (Low-Latency Desktop)"
7. Patch the kernel with the rpi-linux-3.2.21-xenomai-2.6.1.patch
   patch -p1 ...
8. Apply the xenomai 2.6.1 Patch
   $xenomai_root/scripts/prepare-kernel.sh --arch=arm \
   --adeos=$xenomai_root/ksrc/arch/arm/patches/ipipe-core-3.2.21-arm-1.patch \
   --linux=$linux_tree
9. Compile the kernel and the kernel modules (higher priorities with nice could make the compiler process faster)
   nice -n -10 make && nice -n -10 make modules
10. Copy the Kernel Image into /boot

Sources:
http://www.raspberrypi.org/phpBB3/viewtopic.php?t=12368&p=154691
http://elinux.org/RPi_Kernel_Compilation