Open Source Automation Development Lab
You are here: Home / Projects / 
2015-04-28 - 16:19

Next OSADL Events:

Breaking News:

2014-11-18 00:00

Linux real-time: New stable release available -

but next one depends on more support from industrial users


2014-04-09 12:00

First LCA certificate issued

Major automation provider passed OSADL License Compliance Audit


2014-01-20 12:00

Good news from OIN

The Linux Defense Department



OSADL Projects

OSADL Project: Realtime Linux

Rationale

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:

  • 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 real-time PREEMPT_RT patches for mainline Linux developed among others by Ingo Molnár and Thomas Gleixner and now maintained by Thomas Gleixner and coworkers. We believe that long-term stability can only be achieved when the real-time aspects are as close to the vanilla kernel as possible.

Some more information on the PREEMPT_RT patches

General road map of the main patch components

Architecture

x86

x86/64

powerpc

arm

mips

68knommu

Feature

Deterministic Scheduler

Preemption Support

PI Mutexes

3

High-Resolution Timer

1

1

1

1

Preemptive Read-Copy Update

2

2

2

2

2

2

IRQ Threads

4

4

4

4

4

3,4,5

Raw Spinlock Annotation

6

6

6

6

6

6

Forced IRQ Threads

7

7

7

7

7

7

R/W Semaphore Cleanup

7

7

7

7

7

7

Full Realtime Preemption Support

3

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

Download locations

Mailing list where releases are announced

Installation hints

Let a script do the job for you

All profiles of the OSADL QA Farm Realtime systems contain a button to trigger an on-line script generator. The resulting script can be saved in a local computer and used to download, patch and configure a Linux kernel source tree that corresponds 1:1 to the kernel in use at the particular QA Farm system. The script generation button is located at the bottom of the profile page, e.g. here for the system in rack #0, slot #0.

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.

Precompiled Debian kernels

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.

Quality assurance

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!

Recommended reading

These two articles by Paul E. McKenney are somewhat outdated (2005 and 2007); in consequence, some details are no longer reflecting the current situation of the PREEMPT_RT patches, but the principle is still the same.