Welcome to the Free HDL License project wiki! I expect most discussion and development to take place here. Please edit and comment freely, but only if you agree to your changes and additions being governed by the project's license, currently described in the README file.
HDL designs are conceptually like software source code: They're a human-readable format for expressing functionality, which is mechanically converted into a format which more directly implements that function. If the design is being used with reconfigurable hardware (e.g. an FPGA), the synthesized bitfile is loaded an run much like ordinary software in a stored-program computer. While they might embody some technique protected by patent law, the designs themselves are protected by copyright.
There are enough differences, though, that I'm not sure how well the common existing free software licenses (or other software licenses) map to HDL designs. Words like "compile," "link," "library," "object code," and "header file" don't translate exactly. In general, HDL designs can be used to make either reconfigurable logic device bitfiles or permanently-fixed hardware. When the end product is an ASIC, the software thought model (and licenses) may not apply as well.
The goal of this project is to identify clarifications or improvements which would be helpful for licensing Free Software in HDL forms.
A chunk of HDL code seems to have (at least) the following possible destinies:
The HDL and CPU programming processes are decent analogues, but it's not perfect. This may not matter if you want to treat all derivative works identically. It probably does matter, though, for LGPL-like licenses where it matters how the derived work uses your work.
Many (maybe most?) significant FPGA designs involve some proprietary cores from the FPGA vendor. It's not immediately clear when and to what extent such cores are appropriate for a "free" design:
Disclaimer! I believe the following to be correct, but it's only my lay interpretation.
Software licenses (free or otherwise) are based almost entirely on copyright law. Almost any conceivable use of an electronic file is considered copying, at least under U.S. law, meaning that a would-be user needs to (a) have a license and (b) comply with its terms in order to be legal. While this is still true for the HDL files describing a design, the acts of manufacturing a device based on the design, or using such a device, are not subject to copyright. Open hardware licenses attempt to work around this by either licensing patent rights (when they exist) or by attaching future obligations on developed hardware to the copyright license of a hardware design. I don't claim to understand the subtleties here, but the high-level point is that a copyright license may not give the licensor the same leverage as it does for software.
Here are a couple of work-in-progress licenses: