I wanted to share some notes on patching the Linux Libre kernel with realtime capabilities. The Linux-Libre project pulls out all the un-free bits from standard Linux. Contrary to popular belief, Linux has many non-free parts, small binary or obfuscated pieces of code for various hardware. I have a Lenovo T61 laptop. I removed the Intel wireless pci express card and put in a Atheros AR5008 wifi card using ath9k completely free wireless driver. Now my system (as far as I can tell:-) is completely free.
I make music and the realtime patch makes the latency of my system and soundcard very low. This is a unique advantage that the gnu/linux operating system gives its users. I highly recommend a realtime patch for anyone working with audio and video on gnu/linux.
Start by getting the rt patch http://www.kernel.org/pub/linux/kernel/projects/rt/ for the kernel version you want to compile.
Then get the corresponding Linux-Libre version http://www.linux-libre.fsfla.org/pub/linux-libre/releases/
tar xfvj linux-188.8.131.52-libre1.tar.bz2 cd linux-184.108.40.206 bzcat ../patch-220.127.116.11-rt23.bz2 | patch -p1
Now Linux is patched with realtime
now its time for
from the RT How to:
* enable CONFIG_PREEMPT_RT
* activated the High-Resolution-Timer Option (Attention, the amount of supported platforms by the HR timer is still very limited. Right now the option is only supported on x86 systems, PowerPC and ARM Support are however in queue.)
* disabled all Power Management Options like ACPI or APM (not all ACPI functions are “bad”, but you will have to check very carefully to find out which function will affect your real time system. Thus it’s better to simply disable them all if you don’t need them. APM, however, is a no-go.) NOTE: Since rt patch 2.6.18-rt6 you will probably have to activate ACPI option to activate high resolution timer. Since the TSC timer on PC platforms, as used in the previous versions, are now marked as unsuitable for hrt mode due to many lacks of functionalities and reliabilties, you will need i.E. pm_timer as provided by ACPI to use as clock source. To activate the pm_timer, you can just activate the ACPI_SUPPORT in menuconfig and deactivate all other sub modules like “fan”, “processor” or “button”. If you have an old pc, which lacks ACPI support, you migh have problems using the high resolution timer.
I personally have not removed my power management options, as I use a laptop and want these features. I don’t notice any problems but have not tried it without them to know what I’m missing.
then compile the kernel, the debian way
fakeroot make-kpkg kernel_image
sudo dpkg -i linux-image-18.104.22.168-libre1-lapkah_22.214.171.124-libre1-lapkah-10.00.Custom_i386.deb
~ May your kernel build and your modules have your back ~