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Re: [Qemu-devel] Missing ARMv6 instructions?

From: Wolfgang Schildbach
Subject: Re: [Qemu-devel] Missing ARMv6 instructions?
Date: Thu, 30 Mar 2006 11:22:37 +0200

The way I understand this is that anyone who got ARM documentation with 
the license that Paul mentioned, could not contribute patches that 
implement v6 emulation. If, however, someone else (who has not signed such 
a license) were to buy documentation about the ARMv6 architecture that 
comes without a license (for example, the "ARM System Developer's Guide", 
by Sloss, Symes, and Wright, Elsevier 2004), that someone should be able 
to contribute (at least in those aspects of the ARM that are disclosed by 
the book). In that case, ARM should not have any legal hooks except 
copyright, and since at that point you are not using any of their code, 
there is no case. However, I am not a lawyer, so don't take my word for 

As to the threats to ARM's business model, I could see them threatened if 
someone emulated the ARM on hardware of similar performance (without 
licensing ARM IP) -- that would undermine sales of the real ARM cores, 
depending on the price/performance point of the replacement. Software 
emulation of an ARM core on a 4 GHz Pentium is hardly an alternative to 
buying the real thing, though... I also find it hard to believe that 
building a product competitive to an ARM is possible using a description 
of the instruction set alone.

That said, I agree with Paul that lobbying ARM to change their license is 
probably a better route to go. I believe software emulators like qemu are 
really in ARMs best interest since they support ARM development and 
thereby increase the availability of software for ARM cores.

- Wolfgang

Disclaimer: The views stated above are entirely mine, and do not 
necessarily reflect the views of my employer.

Paul wrote on 30.03.2006 00:01:41:

> > I could understand a claim if someone acquired ARM's documentation
> > under an agreement to not produce an emulator. 
> That's exactly where the restriction comes from.
> Theoretically it may be possible to reverse engineer a good proportion 
> ARMv6 from other sources (eg. gcc). However if that were done it would 
> anyone with access to the real ARM documentation (i.e. me and probably 
> else with any professional/commercial interest in ARM emulation) would 
> unable to contribute to qemu.
> > And if there is a possibility of that - in which countries do they
> > have any weight?  Dare I suggest encouraging the development of
> > patches they don't like to countries where they have no legal weight?
> I don't think that's particularly helpful or practical suggestion.
> Better would be to lobby ARM to allow open source emulators. 
> "I'd like to use ARM hardware for <big project>, but qemu doesn't 
> ARMv7 so I'm thinking of using PowerPC instead" is a particularly good 
> argument ;-)
> Paul
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Wolfgang Schildbach, Senior Research Engineer
Coding Technologies GmbH

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