OSADL Project: Realtime Linux

Is realtime possible with Linux? Yes, it is. But which Linux derivate should I use? This is the key question to be answered when Linux is going to be used in the automation industry.

The OSADL criteria for realtime Linux are:

• Strong and agile community
• Long term availability
• Ease of use (user space realtime)
• POSIX API for real time (standard API)
• Wide architecture support
• Mainstream support by the Vanilla Kernel

This project supports the evolution of the realtime preempt patch maintained by Ingo Molnar, and Thomas Gleixner. We believe that long term stability can only be achieved when the realtime aspects are as close to the Vanilla Kernel as possible.

This is the current status of Realtime Linux using the Realtime Preempt patches (aka PREEMPT_RT):

Available in mainline Linux
Available when Realtime Preempt patches applied

1) Since kernel 2.6.24 in mainline Linux
2) Since kernel 2.6.25 in mainline Linux
3) Realtime-Preempt patches 2.6.24.7-rt15 or higher required
4) Since kernel 2.6.30 in mainline Linux
5) Not yet adapted to generic interrupt code
6) Since kernel 2.6.33 in mainline Linux
7) Since kernel 2.6.39 in mainline Linux

• The Linux Kernel: Linux Vanilla Kernel
• The Real Time Preempt Patch: RT Preempt Download Page at kernel.org
• Web Git: heads/rt/2.6.33

OSADL gratefully acknowledges that its member Pengutronix is providing precompiled realtime Linux kernels for Debian distributions. Details are available at the related section of Pengutronix's Website. Currently, the architectures

• 486
• 686
• 686-bigmen
• amd64

are supported.

Quick overview

A quick list of the commands needed to download, patch and build an RT-Preempt realtime Linux kernel is given here.

HOWTO

A more detailed description how to equip the Linux kernel with realtime capabilities is given here.

Stability and capabilities of Realtime Linux are continuously monitored on a number of different computer boards and processor families in the OSADL testing labs also known as the "OSADL QA Farm". One of the labs has a direct link to the OSADL Web server; this makes it possible to display the quality assurance data on realtime in real time here!

• Wiki
• RTAI
• Xenomai
• Linux RT Users Mailing List (Majordomo)
• Linux RT Users Mailing List (Archive)
• "A realtime preemption overview" by Paul E. McKenney
• "SMP and Embedded Real Time" by Paul E. McKenney