eCos User Guide
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# Chapter 3. eCos Licence Overview

As of May 2002, eCos is released under a modified version of the well known GNU General Public License (GPL), now making it an official GPL-compatible Free Software License. An exception clause has been added to the eCos license which limits the circumstances in which the license applies to other code when used in conjunction with eCos. The exception clause is as follows:

     As a special exception, if other files instantiate templates or use macros
     or inline functions from this file, or you compile this file and link it
     with other works to produce a work based on this file, this file does not
     by itself cause the resulting work to be covered by the GNU General Public
     License. However the source code for this file must still be made
     available in accordance with section (3) of the GNU General Public
     License.

     This exception does not invalidate any other reasons why a work based on
     this file might be covered by the GNU General Public License.

The goal of the license is to serve the eCos user community as a whole. It allows all eCos users to develop products without paying anybody anything, no matter how many developers are working on the product or how many units will be shipped. The license also guarantees that the eCos source code will always be freely available. This applies not only to the core eCos code itself but also to any changes that anybody makes to the core. In particular, it should prevent any company or individual contributing code to the system and then later claiming that all eCos users are now guilty of copyright or patent infringements and have to pay royalties. It should also prevent any company from making some small improvements, calling the result a completely new system, and releasing this under a new and less generous license.

The license does not require users to release the source code of any applications that are developed with eCos. However, if anybody makes any changes to code covered by the eCos license, or writes new files derived in any way from eCos code, then we believe that the entire user community should have the opportunity to benefit from this. The license stipulates that these changes must be made available in source code form to all recipients of binaries based on the modified code, either by including the sources along with the binaries you deliver (or with any device containing such binaries) or with a written offer to supply the source code to the general public for three years. It is perhaps most practical for eCos developers to make the source code available online and inform those who are receiving binaries containing eCos code, and probably also the eCos maintainers, about the location of the code. See the full text of the GPL for the most authoritative definition of the obligations.

Although it is not strictly necessary to contribute the modified code back to the eCos open source project, we are always pleased to receive code contributions and hope that developers will also be keen to give back in return for what they received from the eCos project completely free of charge. The eCos maintainers are responsible for deciding whether such contributions should be applied to the public repository. In addition, a copyright assignment is required for any significant changes to the core eCos packages.

The result is a royalty-free system with minimal obligations on the part of application developers. This has resulted in the rapid uptake of eCos. At the same time, eCos is fully open source with all the benefits that implies in terms of quality and innovation. We believe that this is a winning combination.

# Questions and answers

The following queries provide some clarification as to the implications of the eCos license. They do not consititute part of the legal meaning of the license.

Q. What is the effect of the eCos license?

A. In the simplest terms, when you distribute anything containing eCos code, you must make the source code to eCos available under the terms of the GPL.

Q. What if I make changes to eCos, or write new code based on eCos code?

A. Then you must make those changes available as well.

Q. Do I have to distribute the source code to my application? Isn't the GPL "viral"?

A. You do not have to distribute any code under the terms of the GPL other than eCos code or code derived from eCos. For example, if you write a HAL port based on copying an existing eCos HAL in any way, you must make the source code available with the binary. However you would not need to make available any other code, such as the code of a wholly separate application linked with eCos.

Q. I would rather stick with the RHEPL code, but I updated my anonymous CVS checkout.

A. You can check out the final version of anonymous CVS before the license change using the CVS tag `last-rhepl`. See the anonymous CVS access page for details.

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