Real-time Free Software solutions are moving forward with the first release of ADEOS[1], a hardware abstraction layer allowing a real-time kernel and a general purpose kernel to co-exist. RTAI[2] will eventually use ADEOS services, thus offering a real-time kernel based on a principle clearly different from the 5,995,745 US Patent[3].

ADEOS implements a combination of principles[4] published in the early nineties. A core idea was described in the SPACE 1991[5] proposal and consists of a tiny layer that dispatches the hardware resources between multiple concurrent operating systems. ADEOS is a nanokernel that can service a real-time kernel with the highest priority and a general purpose kernel with the lowest priority. Some Free Software real-time solutions favored a different approach where the real-time kernel runs the general purpose operating system, as described in claims 1 and 7 of the 5,995,745 US Patent (1996).

Philippe Gerum implemented ADEOS and released it under the GNU GPL in June 3, 2002[1]. "My primary motivation was to be able to keep contributing Free Software using a patent free technology. My work was directly inspired by Karim Yaghmour's[6] paper published in February 2001[4]. It grounded the implementation onto an original and solid theoretical background" says Philippe Gerum.

Often a piece of Free Software, into which many people have invested years of work, can be turned into non-free software by a patent for one simple but essential calculation rule. Our example shows that the developers need not always give up. Sometimes, by trying very hard, an alternative calculation rule that does the work and is not completely useless can be found. Developers should not shy the efforts that this takes, because even if the patent owner offers a license on friendly terms, usually the project will be restricted in some way or other and the intentions of the developers to create real Free Software will be betrayed.

Feeling certain that ADEOS freedom cannot be jeopardized in the future, Paolo Mantegazza, coordinator of the Italy based RTAI[2] project, has decided to integrate it. "Software patents are illegal in Europe and must remain so because they hinder innovation and overcharge small business and people. US and Japan do not share our good fortune and RTAI will be happy to provide them with a patent free solution" says Paolo Mantegazza.

Like any software, RTAI is threatened by software patents and there is virtually no way to figure out which one is going to strike next. Continuous efforts to keep software free of patents bring these problems to the attention of the public. It is hoped that other countries will follow the example of Europe by ruling out software patents entirely.

[1] http://www.freesoftware.fsf.org/adeos/
[2] http://www.aero.polimi.it/~rtai/
[3] http://patft.uspto.gov/netacgi/
nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/
srchnum.htm&r=1&f=G&l=50&s1=%275,995,745%27.WKU.&OS=PN/
5,995,745&RS=PN/5,995,745
[4] http://www.opersys.com/ftp/pub/Adeos/adeos.ps
[5] http://citeseer.nj.nec.com/probert91space.html
[6] http://www.opersys.com/

About Philippe Gerum: Philippe is the main author and maintainer of the Xenomai (http://freesoftware.fsf.org/projects/xenomai/) and CarbonKernel (http://freesoftware.fsf.org/projects/carbonkernel/) Free Software projects, respectively aimed at real-time operating systems emulation and simulation. He can be reached at rpm@xenomai.org.

About RTAI: RTAI is a Free Software project (http://www.aero.polimi.it/~rtai/) coordinated by Paolo Mantegazza from the DIAPM (Dipartimento di Ingegneria Aerospaziale - Politecnico di Milano), providing a comprehensive real-time application interface in the GNU/Linux environment. He can be reached at mantegazza@aero.polimi.it.