1.3. Linux Kernel
I use a 2.6.26.5 (see my .config). In fact, I upgrade the kernel each time a new release is out. I will assume you are confident in building/installing a Linux kernel. With 2.6.x it is generally no more than doing:
$ make menuconfig
$ make
$ su
# make modules_install
# make install
# vi /boot/grub/menu.lst
But to build a Linux Audio Kernel there is some more work to do.
1.3.1. Realtime Preemption patch
Realtime Preemption Ingo Molnar's Linux kernel patch which tries to improve realtime performance of the Linux kernel.
 | With my configuration and the last Linux kernel (2.6.26.5) I work without needing this patch. |
Always download the last release here. Then apply it:
$ cd /usr/src/ $ wget http://people.redhat.com/mingo/realtime-preempt/patch-2.6.26.5-rt9 $ rm linux $ mv linux-2.6.26.5 linux-2.6.26.5-rt9 $ ln -s linux-2.6.26.5-rt9 linux $ cd linux/ $ patch -p1 < ../patch-2.6.26.5-rt9
Patch should apply without fatal problems. Messages like Hunk #3 succeeded at 652 (offset 1 line). are ok. Search for outputs like Failed. The most common failure is on the Makefile file. Just edit it by hand and add -rt9 at the end of the EXTRAVERSION variable.
1.3.2. Configuration
 | Do not forget to adapt those samples to your own configuration (especially for the "PCI devices" section). |
The most important items for a vanilla Linux kernel (not patched with Ingo's RT patch) are:
Processor type and features --->
Preemption Model (Preemptible Kernel (Low-Latency Desktop)) --->
[*] Preempt The Big Kernel Lock
Timer frequency (1000 HZ) --->
Device Drivers --->
Character devices --->
<M> Enhanced Real Time Clock Support
<M> Generic /dev/rtc emulation
[*] Extended RTC operation
<M> Real Time Clock --->
[*] /sys/class/rtc/rtcN (sysfs)
[*] /proc/driver/rtc (procfs for rtc0)
[*] /dev/rtcN (character devices)
<M> PC-style 'CMOS'
Sound --->
<M> Sound card support
Advanced Linux Sound Architecture --->
<M> Advanced Linux Sound Architecture
<M> Sequencer support
<M> Sequencer dummy client
<M> OSS Mixer API
<M> OSS PCM (digital audio) API
<M> RTC Timer support
[*] Use RTC as default sequencer timer
Generic devices --->
<M> Virtual MIDI soundcard
PCI devices --->
<M> RME Hammerfall DSP Audio
Security options --->
[*] Enable different security models
<M> Default Linux Capabilities
For a kernel patched with Ingo's RT patch the differences are:
General setup --->
[*] Enable concurrent radix tree operations
[*] Enabled optimistic locking
Processor type and features --->
[*] Enable priority boosting of RCU read-side critical sections
Also for RT patch you must uncheck the folloging options:
Processor type and features --->
[ ] Enable tracing for RCU - currently stats in debugfs
Device Drivers --->
Character devices --->
[ ] Real Time Clock Histogram Support
< > Parallel Port Based Latency Measurement Device
Kernel hacking --->
[ ] Wakeup latency timing
[ ] Non-preemptible critical section latency timing
[ ] Interrupts-off critical section latency timing
1.3.3. Installation
Install modules and kernel and edit the /etc/modules file to add the following content, depending on your hardware:
rtc
snd-rtctimer
snd-hdsp
snd-hwdep
snd-page-alloc
snd-pcm
snd-rawmidi
snd-seq
snd-seq_device
snd-seq_midi
snd-seq_midi_event
snd-timer
Most of these modules depend on others that will be automatically loaded.
Most of time you would also raise the value of the max-user-freq kernel value. To do so you can either:
Use sysctl by editing /etc/sysctl.conf and adding the following line:
dev.rtc.max-user-freq=1024Once the file is updated, reload the configuration by running sysctl -p as root user.Directly write the value into /proc/sys/dev/rtc/max-user-freq at boot time:
echo 1024 > /proc/sys/dev/rtc/max-user-freq
Now just reboot on your new kernel.