RTAI and the RT-Linux patent
The following statement by Eben Moglen, General Counsel of the Free Software Foundation clearifies the legal situation of RTAI users with regard to the infamous RT-Linux Patent.
Date: Sat, 20 Oct 2001 11:27:14 -0400 (EDT) From: Eben Moglen To: email@example.com Subject: Re: Won't help with what? Thanks for your note. As I have said, we have by no means ignored these issues. We believe on the basis of our own careful review of facts and law, and after appropriate consultation, that there is no cause for concern on either ground. The new patent license allows the teaching of the patent to be practiced without any additional obligations in any program released under GPL. If RTAI is released under GPL, as it can and should be, it is fully protected against any infringement claim by the license we negotiated. Any modified RTLinux system must be GPL'd, because RTLinux is GPL, and thus any RTL system that is distributed in a GPL-compliant manner is also covered by the new license. End of that aspect of the problem. The applications problem also does not exist. Patents, because they grant very long-term and "strong" monopolies, are very precise documents. A patent's "scope," or the extent of its power to exclude others from its teachings, is rigidly limited by its "claims," which are one portion of the document that is negotiated between the inventor and the issuing Patent Office. Anything which is not part of the patent's claims is not covered by the patent, and can be done by anyone anywhere anytime, without regard to the patent. Victor Yodaiken's patent has eleven claims. Each of those claims covers behavior of (1) a real-time OS kernel, (2) a general purpose OS kernel being run as the idle-task of the RT OS, and (3) a software emulator of hardware interrupt control, which allows the RT OS to prioritize and present interrupts to the general purpose OS only when the RT OS has met real-time interrupt requirements. These eleven claims, like all claims in all patents, are written as broadly as possible, so as to bring as much behavior as possible within the scope of the patent. But none of the teachings of the patent, as specified in its claims, is practiced by any applications program running under any OS kernel. No application in a running RTLinux or RTAI system does any of the things the patent claims. No applications program is therefore potentially infringing, and no applications program is covered, or needs to be covered, by the license. If an applications program running in a GNU/Linux system as modified by RTLinux or RTAI is constructed so that it does not violate GPL--which is not the same thing as being licensed under GPL or being free software at all--its distribution terms are utterly irrelevant. I reviewed this issue carefully, as part of my own legal work negotiating the settlement, and I have taken additional advice from patent counsel on this and other aspects of the situation. We would not have completed our arrangements if we had not been fully satisfied on this point. But reality and perception differ. Perhaps Victor has attempted to create the perception that he has more power over others' arrangements than he has. This would not be the first time in the history of business, politics, war or even marriage that such behavior occurred. We are seeking one or two clarifications in statements appearing on FSM Labs' website, which we think might inadvertently contribute to misunderstanding on these points. FSF may also choose in future to make some official statement on these matters. This message summarizes our view of the legal situation, and you may redistribute it, verbatim, freely. Best regards. -- Eben Moglen voice: 212-854-8382 Professor of Law fax: 212-854-7946 moglen@ Columbia Law School, 435 West 116th Street, NYC 10027 columbia.edu General Counsel, Free Software Foundation