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Frequently Asked Questions 4 Licensing 4.1 What license is used for opencores? Each author uses their preferred license. Generally licenses are either GNU or BSD in nature. A BSD style license essentially states that no warranty is given, the core may be distributed in source or binary form and the authors copyright must be acknowledged. The GNU Public License (GPL) adds the important condition that all modifications must be distributed under the GPL. When you release something under the GPL, no-one can take away your right to later access a modified version of it. Conversely, if you use a GPLed item, you MUST distribute all information about it and NOT prevent others from redistributing or modifying it. Stating it as an oversimplification: you cannot keep secrets unless you want your butt sued. Each core will come with a license (usually in a file called 'COPYING'). To understand your obligations, you should read the text the of the license that comes with any core you use. For more information about licenses, see the GNU project (http://www.gnu.org) and the OpenSource Initiative (http://www.opensource.org). To simplify life for users, developers are strongly encouraged to use an unmodified GPL or LGPL (Lesser GPL) license or the modified BSD license. The 'modified' BSD license is the original BSD license with the 'advertising clause' removed. Documentation authors are encouraged to use the GPL or FDL (Free Documentation License).