Frequently Asked Questions about the CERN Open Hardware Licence
Frequently Asked Questions about CERN OHL v2
Special section for COVID-19 developers
We are going to include this section here temporarily to help people who are developing hardware for fighting COVID-19. After the crisis, we will dispatch these questions to the relevant sections:
Q: Why should I use a licence?
A: If you put your files out there, be it on github, ohwr.org, gitlab.com or anywhere else, copyright law applies by default. Unless you explicitly give permission to, people will not have the right to copy them, modify them, publish the modifications, make hardware based on the design files, commercialise it, etc. You give this permission through a licence. There are ready-made licences you can use for this purpose.
Q: Why should I use the CERN Open Hardware Licence v2?
A: Because it is the newest Open Hardware Licence, it incorporates the latest thinking of many experts on what makes an Open Hardware licence good and it acknowledges, through the use of three variants, the different sharing schemes you might want to use in your project. See this other FAQ entry for other reasons, in particular if you are considering or already used a non-hardware licence.
Q: How do I license my material in practice?
A: After you have decided which variant of the licence you would like to use, go to the licence page and see the user guide corresponding to that variant.
Q: My project includes hardware and software. How do I make sure the whole product is distributed together and stays open source?
A: A quick clarification first: we use the word "firmware" sometimes for software which is permanently stored in a ROM or flash memory in a product. All our discussion about software applies fully to firmware because firmware is software. We do not use the word "firmware" when we discuss the design of Field-Programmable Gate Arrays (FPGA) or Application-Specific Integrated Circuits (ASICs) using Hardware Description Languages (HDL). For those cases, we use the word "gateware".
The CERN OHL v2 was designed to fill a gap in the licensing scene. It allows hardware designers to efficiently share hardware designs. It also works very well with gateware. Those are the natural domains for CERN OHL use. In addition, we made sure during its drafting that it could also be used for software. Having said that, there are already very good licences for Free and Open Source Software (FOSS), so chances are your software base is already using one of those, or you prefer to use a well-established software licence for any other reason.
If you are trying to pick a good FOSS licence for the software part of your project, here are our recommendations:
GPL3-or-later if you want a strongly-reciprocal software licence.
LGPL3-or-later or MPL2 if you want a weakly-reciprocal software licence.
Now, if you have gone through the discussion material on CERN OHL v2, you may have come across the concept of "Available Components" and you may be wondering if software is a component of your hardware design. The answer is "no, it isn't". Software is not a component of the hardware design, the same way that the orange juice you pour into a bottle is not a component of the bottle design. So all the discussion about "Available Components" does not apply here. The software and hardware parts of a project have independent licensing regimes.
So, how can you, as a licensor, make sure that software and hardware design files travel together, under open-source licences, as people modify them and ship products based on the them? There are two things you can do:
License your software under a strongly-reciprocal licence such as GPL3, which ensures that improvements are fed back to the community when products are distributed. You can also use a weakly-reciprocal licence such as LGPL3 if you want to allow people to combine your software with proprietary (non-open-source) developments. It would, of course, be helpful if the source code of the software part of your product were provided in the Source Location of the hardware design, or through a link available in it.
In addition, you may, to give recipients additional comfort, have your product certified under the Open Source Hardware Association (OSHWA) certification program, which stipulates that the hardware part of a project should be licensed under an Open Hardware licence and the software part should be licensed under a Free and Open Source Software licence. Others will still be able to take your hardware, use proprietary software in it instead of the software you provided, and ship the result as a product, but they will not be able to use the version of the OSHWA certification logo that incorporates your certification ID.
Q: We are designing a ventilator within our company. We plan to include our company logo in a PCB silk screen. What happens to the logo if other people build and distribute the ventilator? What if they build and distribute a version of the ventilator for which they modified the design files?
A: If you publish a design including a silk screen for the PCB, then you may want to consider excluding your logo if you don’t want it reproduced, or, if you do, but only on a non-modified version of the circuit board, then you can include two versions of the silk screen, one with your logo, and one without (of course, remember that even if someone makes a non-modified PCB, they may do so badly, and in a way which reflects badly on you). The version without the logo is the version you should provide under the CERN-OHL together with the rest of the design files.
You may then want to consider a separate licence for use of the logo. You can grant this on a case-by-case basis, or have a general policy. This is a common approach in the world of Open Source, especially so far as certification is concerned: for example, the Open Source Hardware Association only permits the use of their logo on certified hardware. You may like to consider your own certification programme, by which you license the use of the term “<your company> Certified” to those manufacturers complying with your certification programme. Each of the CERN-OHL variants contains a section prohibiting licensees from using the name of CERN or the Licensor to suggest any implication of endorsement or involvement with the project, but if you include your logo in a silk screen print which you license under CERN-OHL, you will confuse licensees by providing a potential conflict with this section.
Note also that in many jurisdictions, failing to provide appropriate quality control over anyone who is permitted to use your name or logo may have adverse legal consequences. If you do want to license the use of the your logo to others, please do not try to do so under the CERN-OHL, and do take appropriate legal advice.
CERN OHL v2 general questions
Q: What does CERN OHL try to achieve?
A: The CERN Open Hardware Licence aims at providing a solid legal basis
for the sharing of hardware designs. In this release, we intend to give
Licensors different options for the sharing mechanism: strongly
reciprocal, weakly reciprocal and permissive.
Q: What are all these suffixes?
In the software domain, there are three generally acknowledged licensing
regimes for free and open source software: permissive, weak copyleft and
strong copyleft. There are tastes and use cases for each option, and the
same happens in hardware. We use the word "reciprocal" instead of
"copyleft" because the underlying rights in our case are not restricted
to copyright. So, when you use the licence, you need to add a Notice to
your designs with one of the three following suffixes: S, W or P:
CERN-OHL-S is a strongly reciprocal licence. For example, if you
release HDL files under CERN-OHL-S and then somebody uses those
files in their FPGA, when they distribute the bitstream (either
putting it online or shipping a product with it) they need to make
the rest of the HDL design available under CERN-OHL-S as well.
CERN-OHL-W is a weakly reciprocal licence. For the example above, if
you release your part of the design under CERN-OHL-W, somebody who
distributes a bitstream which includes your part does not need to
distribute the rest of the design files as well.
CERN-OHL-P is a permissive licence. It allows people to take your
code, relicense it and use it without any obligation to distribute
the sources when they ship a product.
Q: What is the scope of CERN OHL?
A: The licence is meant to cover Open Source Hardware (OSHW) designs. It
has no concern with proprietary developments. When we drafted it, we
also made sure it can be used for free and open source software, even if
that is not its main aim.
Q: What are the rights the licence rests upon?
A: The licence texts make no assumptions about the rights that will be
invoked to sustain them. These may include but are not limited to
copyright, patents, design rights and database rights.
Q: Why is CERN doing this?
A: One of the most important parts of CERN's mandate is knowledge
dissemination. OSHW is a natural way to disseminate hardware designs
done at CERN to the rest of society. It is also important that a licence
such as CERN OHL is stewarded by an institution whose mandate and values
can guarantee its stability over
Q: Why not use existing licences such as GPL and any in the family of Creative Commons licences?
A: The CERN OHL was drafted with hardware in mind. The fact that the
licensed materials are going to take part in the process of creating
hardware has various implications. For example, the presence of patents
is more pervasive in the hardware world than in software or in works of
art. The CERN OHL appropriately has a patent licensing section, which is
lacking for example in CC licences. What does this mean in practice? If I release a design for which I hold patents under, say, CC-BY-SA, and you take it and use it, e.g. to build hardware and commercialise it, I can sue you for patent infringement. The CERN OHL v2 contains a patent licence, i.e. a promise of the licensor to all potential licensees that they can use the design without fear of being sued for patent infringement in that design by the licensor. The CERN OHL v2 also contains a patent retaliation clause: licensees who sue the licensor for patent infringement automatically lose their rights under the licence.
The realities of hardware design in
terms of design tools are also very different from those of software. It
is for example very common to design Application Specific Integrated
Circuits (ASICs) using proprietary tools with proprietary libraries
which are an integral part of the final design. Something similar
happens with the design of Field Programmable Gate Arrays (FPGAs). PCB design is also often done using proprietary tools. These
realities need to be taken into account in the drafting of the licence
if we don't want a strongly reciprocal licence which can only apply in
an extremely reduced number of cases.
Finally, it is important for a
licence to contain text that practitioners can easily relate to. The
CERN OHL strives to use clear terms and definitions that have easily
recognisable and intuitive meanings for hardware designers.
Q: Will you seek OSI and FSF approval/endorsement?
A: Yes, we want the CERN OHL to be as respectful of the four freedoms
and the Open Source Definition as established free and open source
software licences. The process of getting endorsement or approval from
these respected institutions will surely make the licence
Q: Is this licence a contract? If it is, what is the consideration in this contract?
A: Yes, the CERN OHL is a contract. Bare licences don't exist in civil
law countries. Both Licensors and Licensees have obligations under the
CERN OHL which count as consideration.
Q: Who has the right to enforce this licence?
A: In free and open source software licences, it is the rights holders
(typically copyright holders) who are able to enforce the licence
against infringers. People who receive the code, unless they are also
contributors, cannot (for example, if you receive GPL code and want
access to the source code, you have to find a rights holder in the code,
and get them to complain about the non-conformance). You are not able to
do that yourself. The CERN OHL adopts the same rationale. However, a
relatively simple licence text change would potentially allow recipients
of Products and Covered Source to enforce against whoever they received
them from. Our concerns are that this would potentially open any
contributors up to potential liability from downstream recipients, and
thus limit licence adoption, but it is an issue which should be
understood and discussed before a final decision is made for this
Q: I am a user of CERN OHL version 1.2. What are the main changes introduced by this new version?
A: Version 2 of the CERN OHL improves on version 1.2 in various respects:
The new version comes in three variants: strongly reciprocal, weakly reciprocal and permissive. Reciprocal licences stipulate that changes to a design must be fed back to the community, for everybody to benefit from them. Permissive licences do not impose this condition. In this way, CERN OHL v2 caters for the different collaborative models currently used in Open Source Hardware projects.
In the reciprocal variants, it is very important to clarify the scope of reciprocal obligations. By introducing the concepts of "Available Component" and "External Material", plus the already-existing concept of "Product", the new version makes a special effort to clarify what sources should be shared in both the -S and -W variants.
CERN OHL version 1.2 included a patent licence, i.e. a promise by the licensor that (s)he will not sue a licensee for patent infringement as regards the design licensed under CERN OHL. Version 2 adds a reciprocal clause for this patent licence: if a licensee sues a licensor for patent infringement, (s)he loses all the rights granted by the licence.
In licence 1.2 we did not make a special effort to cater for Hardware Description Language (HDL) development as used in Field Programmable Gate Array (FPGA) and Application-Specific Integrated Circuit (ASIC) design. As we became convinced that there was no appropriate reciprocal licensing regime for HDL, we made sure that CERN-OHL-S and CERN-OHL-W can provide a good solution for FPGA and ASIC designers with a reciprocal mindset.
Version 2 makes a special effort to maximise the chances that the recipient of a physical product will get access to the design files for that product. It does this by granting the licensor the possibility of embedding a URL or another reference in the object itself, and establishing that downstream licensees should respect that notice and update it as applicable if the design is changed.
The new version provides a grace period of 30 days for licensees which infringe in terms. If they come into compliance within 30 days after receiving a notification from the licensor, their rights are reinstated. This is meant to help with cases in which a licensee infringes the terms of the licence inadvertently.
Q: I am using one of variants of CERN OHL v2. What is the licence of the licence text itself?
A: The licence is copyright (c) CERN 2020, and the text of the licence is licensed as a whole under a Creative Commons Attribution-NoDerivatives 4.0 International Licence, (CC BY-ND 4.0), available at https://creativecommons.org/licenses/by-nd/4.0/
As a special exception to that licence, CERN expressly permits faithful translations of the entire licence into any language, and subsequent public display and distribution, provided that the resulting translation (which may include an attribution to the translator) is released under CC BY-ND 4.0 attributing CERN as the copyright holder, and providing a link to the original licence text at https://ohwr.org/cern_ohl_s_v2.txt (for the S variant), https://ohwr.org/cern_ohl_w_v2.txt (for the W variant) or https://ohwr.org/cern_ohl_p_v2.txt (for the P variant). This paragraph (translated appropriately) must be included when copying or translating the licence. If you carry out such a translation, you must make it clear (by at least including this paragraph) that the translation is unofficial and that the original text of the licence in the English language as released by CERN is definitive. You may also extract parts of the licence text (both in the original and in faithful translation) and copy, publicly display and distribute them for the purposes of education, training, providing legal advice, reviewing and critiquing the licence provided that you attribute CERN as above and also provided that such extracted parts do not form part of any document intended to have legal effect.
Questions about hardware licensing
Q: Copyright does not cover hardware. How do you implement strongly reciprocal licensing in CERN-OHL-S?
A: Roughly speaking, the hardware equivalent of a binary object in the
free and open-source software world would be a tangible object made
thanks to design files licensed under an OSHW licence. So implementing a
reciprocal licence involves solving the challenge of ensuring that the
recipient of a piece of hardware gets access to the original design
files. This is tricky because copyright law (which is the mechanism used
by most software licences to impose obligations on licensees) does not
apply to hardware production and distribution. In drafting CERN-OHL-S,
we have made a special effort to achieve this effect by relying solely
on existing and applicable rights, and we believe the licence will
fulfil this part of its purpose in a large number of cases. Read on to
learn how CERN-OHL-S provides two mechanisms for a recipient of
hardware to get hold of design documents:
The licence explicitly asks a Licensee to provide an easy way to
access the design Source to recipients of products when (s)he makes
and distributes products based on CERN-OHL-S licensed designs.
For cases in which a tangible piece of hardware changes hands many
times before reaching the final recipient, it is impossible to
enforce the obligations above without making the licence text much
more complicated and incurring in many extra contractual relations.
The original designer though, can make it much more likely for the
recipient to get access to the design files by including a URL or
similar in the design, in a place where it will result in a visible
imprinted label in the final object. The CERN-OHL-S requests that
downstream Licensees respect that Notice and modify it accordingly
if they modify the design files. It also requires that they make the
Complete Source for the Product available to the recipient of any
Product. The easiest way to do this, and the one which we encourage,
is to make the Complete Source available from a Source Location
(which is typically a public repository). However, it is also
possible (although more cumbersome), to distribute Source and a
Product privately, so long as the recipient is provided with a copy
of the Complete Source.
Methods to enforce the licence will depend on each case. For example,
most of the hardware designs are likely to be stored and distributed in
the form of design files, i.e. digitally, and doing just about anything
with them is going to involve copying, at a minimum, which will require
a licence, and therefore allows the licence to impinge. Once the
licensee exercises any rights under the licence, the whole licence text
applies, including obligations at production and distribution time. This
is just one example involving copyright, but as we said in an answer to
another question, there may be more rights the licence rests upon in
each case. It is important for a licensor to understand how the licence
is intended to work and what can and cannot be achieved for a particular
design in a particular context. No licence gives licensors 100%
reassurance of what will happen in court one day, and the CERN OHL is
not an exception in that
Q: Are there types of hardware that may not lend themselves to the CERN-OHL licences?
A: Copyright protection can apply unevenly to hardware. As a result, the CERN-OHL licences focus on Source and Covered Source. These types of documentation for hardware are much more clearly protected by copyright.
One result of this focus is that the obligations created by the CERN-OHL licences are strongest when someone modifying or building upon the licensed hardware would normally do so by modifying the Source. For example, someone modifying a PCB is likely to start with the source file for the original PCB licensed under the CERN-OHL instead of trying to recreate the file from scratch by examining the PCB itself.
Other types of physical objects are not as reliant on Source for modifications. For example, someone modifying a crowbar might choose to recreate documentation instead of starting with the originally licensed documentation.
While these types of directly modified hardware are edge cases, their limited relationship with their underlying documentation make it less likely that their licensing requirements can be easily enforced. If you are working with these types of hardware it may be better to focus on the CERN-OHL-P licence. That licence removes any ambiguity around the hardware’s rights without attempting to impose unenforceable obligations on downstream users.
Q: What can I do to ensure that people who receive a piece of hardware I designed get access to the design files?
A: You would have to use the -W or -S variants, and include in your distribution a Notice saying you want Products to display the Source Location for your design files and how that should be done for the particular bit of hardware your design files represent. Section 4 in the -W and -S texts gives permission to Make and Convey Products, and specifies that your Notice should be honoured:
If specified in a Notice, the Product must visibly and securely display the Source
Location on it or its packaging in the manner specified in that Notice.
If you are not the original designer, you can also take the design and modify it (therefore becoming a Licensee), adding a Notice for the display of the Source Location before distributing the resulting modified design (therefore becoming a Licensor).
Q: My PCB is made of ICs, which are made of plastic, metal and a chip, which is itself made of silicon. How far do I need to go in terms of providing the source designs for all this?
A: The ICs in your design qualify as "Available Components" in
CERN-OHL-S and CERN-OHL-W (the two cases where this question makes
sense). Therefore, as a Licensee, you can reference them (as when you
draw a symbol for them in a schematic) without any need to distribute
their associated sources. In this case the IC may be a custom design
also licensed under CERN OHL, but that is an independent decision of its
Q: What are "Available Components"?
A: "Available Components" in CERN OHL play a similar role to "System Libraries" in GPL/LGPL. These are components that we assume people generally have access to. As such, people can recreate a Product by using CERN OHL licensed designs and getting these Available Components separately. A resistor is a typical example of an Available Component. In reciprocal licences such as CERN-OHL-W and CERN-OHL-S, it is important to clearly define the scope of the reciprocal obligations. The concept of Available Component is key in that regard. If you take a CERN OHL licensed design and modify the value of a resistor, you don't need to release the resistor design itself. This is because Available Components are excluded from the reciprocal obligation of releasing the sources. This makes the reciprocal licences more practical to work with, since many of these Available Components are proprietary and access to their design sources, and the right to distribute them, is very limited in most cases.
Incidentally, the definition of "Available Component" is one of the few places where CERN-OHL-W and CERN-OHL-S differ. Under CERN-OHL-S, only physical parts (e.g. a resistor or an ASIC) qualify as Available Components. CERN-OHL-W allows both physical and non-physical parts (e.g. an HDL core) to qualify as an Available Component. So e.g. an FPGA design licensed under CERN-OHL-W can have proprietary cores in it, provided they are Available (e.g. they can be purchased by anybody).
Questions about software
Q: A CERN OHL licensed PCB contains a processor running code. What are the implications on the code of using CERN OHL for the hardware?
A: The CERN OHL licence of the PCB does not extend to the code running in that
processor. The processor falls under the definition of "Available
Component" in CERN-OHL-S and CERN-OHL-W (the two cases where there could
be a potential issue). So does the flash (or other) memory chip that may
host the code prior to power-up. The CERN OHL as applied to the PCB has no concern with the
contents of that flash. You could of course choose to license that code
under a Free and Open Source licence, e.g. GPL, or even under the CERN OHL itself, but that is independent of your choice of licensing for the board as a hardware design.
Q: Are non-open binary software blobs allowed to run in hardware licensed under CERN OHL?
A: This is another way of asking the question above. Yes, they are allowed.
Questions about FPGA and ASIC design
Q: An FPGA design is licensed under CERN-OHL-S or CERN-OHL-W. What are the implications regarding proprietary primitives and macros used in the design?
A: Proprietary blocks readily available in the design tools fall under
the definition of "Available Components" and it is therefore not
required to ship them when you distribute the design sources or products
based on those
Q: An ASIC design is licensed under CERN-OHL-S or CERN-OHL-W. What are the implications regarding proprietary primitives and macros used in the design?
Because of the way primitive libraries (e.g. the so-called
PDKs and standard
cell libraries) are
distributed in the ASIC design world, things are actually quite
different from the FPGA case. Wording in CERN-OHL-S does not exclude
these primitive libraries from the distribution obligations. Not
excluding them makes the resulting licence applicable in only an
extremely reduced number of cases now and in the short-term future:
those where the PDKs and standard cells are released as Open Source
Hardware. Those who would like a reciprocal licence which works with
proprietary PDKs and standard cells should use CERN-OHL-W and not
Q: Is an FPGA bitstream a Product according to the definition of Product in CERN OHL?
A: Yes, a bitstream results from the processing of source files and is
therefore a Product, provided that those sources are licensed under the
Q: I would like to combine CERN-OHL-W and CERN-OHL-S licensed cores in the same FPGA design. Is it possible? What will be the resulting licensing scheme for the top level?
A: Yes, both can be combined, and the licence for the top level will be CERN-OHL-S in order to comply with clauses 3.2 and 3.3.d in the CERN-OHL-S licence under which some of the components are licensed. Furthermore, section 7.3 in CERN-OHL-W says
You may treat Covered Source licensed under CERN-OHL-W as licensed under CERN-OHL-S if and only if all Available Components referenced in the Covered Source comply with the corresponding definition of Available Component for CERN-OHL-S.
so the top level must be CERN-OHL-S in order to comply with both licences.
Questions about patents
Q: I find the section on patents a bit confusing. Can you explain to me in plain words what you are trying to achieve?
The idea is the following: when I give you a set of design files
licensed under CERN OHL, I am promising you that I will not sue you for
infringing any of my patents when you use that design for all purposes
CERN OHL allows (studying, modifying, making hardware, selling it...).
This is meant to reassure you as a Licensee and therefore favour
adoption of designs licensed under the CERN OHL. Conversely, if you sue
me for patent infringement in that particular design, you will lose all
the rights I granted you in the licence. This two-way section on patents
is intended to provide for a reassuring environment when it comes to
sharing hardware designs.
Questions about practical use of the licence
Q: How should I handle Notices?
In general, it is good to keep notices in the design files as simple as
possible. For example, in your circuit schematics you can have in each
page a little square with a notice inside saying "Copyright XYZ, 2018
Licensed under CERN-OHL-S version 2". In the layout, you could have a similar box
in one of the documentation layers. Then, for more involved notices, you
can use a NOTICE text file in the top directory of the project. One
example of such more involved notices would be one where you specify
that you would like the final product to display the Source Location
(e.g. a URL) on it or its
Questions about Termination
Q: What happens to the rights of the Licensees of a Licensor if the rights of the Licensor under this licence are terminated?
A: It's his/her rights as Licensee that terminate. (S)he is still a
Licensor, and therefore the rights of downstream Licensees are not
Questions about distribution
Q: Does private distribution of sources or products trigger any obligations in CERN-OHL-S and CERN-OHL-W?
A: If you distribute a product privately, and the sources for that
product are licensed under CERN-OHL-S or CERN-OHL-W, then you need to
make the sources available to the recipient of that product. No need to
distribute them more widely. The recipient of those sources of course
has the right to make them available to the public (unless you are
using the research and development permission in Section 5 of -S and -W: see the next FAQ below).
Q: I want to engage another engineering company to help me with research and development. Can I do that without that company getting the full set of rights to use and distribute my designs under CERN-OHL?
A: Yes. There are two ways you can provide the designs (Covered Source) to the engineering company: either under section 3 (which is the way you would provide the designs to any third party), or under section 5. Section 5 is an additional permission which allows you to convey the Covered Source to an R&D company under restricted terms (which prevent the engineering company from conveying to any third party, or from using the designs for its own purposes). This means that the engineering company won't acquire the rights any other recipient would normally acquire under the CERN-OHL-S or -W. This lets a company perform research and development for you without the results potentially being made available to anyone else, unless you want them to (without section 5, if you tried to prevent the engineering company either from making their own use of the designs, or from conveying them to any third party, this would be a breach of subsection 2.3, as restrictions on licensees). If you do not comply with the provisions of section 5, then the conveyance will be deemed to be under section 3 and the engineering company will receive the right to use, modify and re-distribute the designs themselves, as if they were any other recipient of those designs.
Questions on licence compatibility
Q: Is CERN-OHL-S compatible with GPL?
A: No. To explain why, let's take the case of an FPGA design. If any block is GPL in that design, all other blocks have to be released under GPL. Same for CERN-OHL-S: one core as CERN-OHL-S would force a distribution of all other cores, along with the top-level design, under that licence. So it's easy to see how a GPL core and a CERN-OHL-S core in the same design would create a problem. This is a well-known issue in the software world, and the reason why people try to avoid the proliferation of different, incompatible, strong copyleft licences.
So, we could add a clause to CERN-OHL-S which says that any design licensed under CERN-OHL-S can be relicensed under GPL by the licensee. This would allow the combination of GPL and CERN-OHL-S in the same design. We decided not to do that for various reasons, in particular:
We think that GPL is not an optimal licence for the case of hardware. For example, in the case described above, after carefully reading the GPL3 text, one could very well argue that any primitive/macro libraries from the FPGA vendor (Xilinx, Altera/Intel...) should be distributed too, which is explicitly forbidden in the licensing of those libraries.
When drafting the CERN-OHL-S and CERN-OHL-W, we took special care to guarantee, to the biggest possible extent, that the recipients of hardware get access to its design files. There are special provisions in the licence texts to ensure that, which don't exist in GPL. One example is the ability for a licensor to specify that the URL for a design should be physically engraved in the final product. Allowing people to relicense under GPL would provide an easy means to escape such obligations. The lack of an appropriate reciprocal licensing regime for hardware was one of the key reasons to draft the CERN-OHL to begin with.
The rationale document explains all this with other words:
We thought hard about compatibility with other licences. An earlier
version of the draft contained a mechanism for options, and a specific
option which allowed compatibility with GPLv3. There’s an easy way to
allow compatibility, of course: you can insert a clause which
explicitly allows relicensing, but this necessarily means that one of
the licences will have characteristics which are more forgiving than
the other, and users can just pick whichever licence they want. If the
original licensor wanted to do this in the first place, they could
simply dual-license under CERN-OHL and GPLv3. We also found that the
mechanism we chose was pretty cumbersome, especially since to make it
work, we needed also to add an additional permission to GPLv3. Since
we’re essentially asking people to relicense their GPLv3 components
anyway (albeit within the mechanism), we felt we should be more
explicit about this.
Q: More specifically, I would like to use a GPL2-licensed core in my design. What are the consequences on the licensing of the rest of the files in that design?
A: If you release a product based on that design, for example if you are shipping a product containing an FPGA whose configuration bitstream has been derived from the GPL2-licensed and other sources, then according to the GPL2 terms, you are distributing the "Program" in object code form. This means you need to provide access to all the sources, and these sources must all be licensed under GPL2. This is where incompatibility issues can arise. Permissive licences such as Solderpad and CERN-OHL-P will allow re-interpreting the licensing terms in the licence so that you can treat the files as licensed under GPL2. Reciprocal licences such as CERN-OHL-W and CERN-OHL-S will not allow this re-interpretation. This makes it impossible to use cores licensed under GPL2 (or GPL3 for that matter) in a design which also uses cores licensed under CERN-OHL-W and CERN-OHL-S.
Questions about CERN OHL v1.2
Q:* What are the main differences between v1.2 and v1.1?
A:* Version 1.2 is lighter on the users of the licence. Now
licensees who modified a design no longer have the obligation to notify
the changes to upstream licensors. In addition to that, in order to
guarantee that recipients of CERN OHL-licensed hardware get access to
the design documents of a specific piece of hardware, version 1.2
includes the notion of Documentation Location. Another difference
between the two versions is that Intergovernmental Organizations such as
CERN are not singled out regarding their rights anymore. This means that
they are as any other licensor or licensee.
Q:* What is the motivation for the sentence "However, the Licensor
shall not assert his rights under the foregoing proviso unless or until
a Product is distributed" in paragraph 3.3?
A:* The Licensee receives a right (to modify the Documentation) upon
the fulfillment of a condition (to make the Documentation available).
Without the sentence above, the obligation for publishing would be
enforced as soon as the modification happens, which would make it
impossible to fulfill.
Questions about CERN OHL v1.1
Q:* We like to publish one of our HW design to the open source.
Therefore we are looking for an “open hardware licence” to be used. In
this process we found the CERN OHL v1.1 which could be a good choice.
In the “Guide to the CERN OHL v1.1” is pointed out that one should
include “Licensed under CERN v1.1” on the silkscreen. To this paragraph
I got the following question:
Is this a MUST ? (The prints are already produced and for further
productions we do not have much empty space on the board)
What is the legal consequence if this is missing?
Does a licensee necessarily need to add the notice on the
A:* The Guide is here to provide guidance and assistance as to how to
apply the CERN OHL.
Indeed, space can be an issue. The idea behind this recommendation is to
have it known that the hardware one would come across is licensed under
CERN OHL. However, under CERN OHL v.1.1, the Documentation must
accompany the hardware that is being distributed (article 4.1) and in
the Documentation, the licence notice must appear, and must not be
removed by licensees (article 3.1).
So to summarise, adding the licence notice is not a requirement, but as
licensor, it is one of the best ways to make it known that the hardware
is Open (Source) Hardware since it may well get ‘separated’ from the
Documentation in its life. The licensee does not have to add the notice
on the silkscreen, however if the licensor has put it there, he may not