Re: [oc] hardware compatibility and patent infringement

[Victor the Cleaner <jonathan@canuck.com>]

> As some people in Opencores are developing cores compatibles with
> designs protected by patents and copyrights I thought it was a good idea
> to ask about "hardware compatibility and patent infringement" in this
> mailing list.

I'm not way up on the current state of things, but these answers 
should provide some useful guidance.
 
> 1. In general, What's the way to design a hardware processor (device)
> compatible with the instruction set (specifications) of another
> processor (device) without infringement of patents?

Read the patent and determine what the claims are.  There can be no
"rule of thumb" that's guaranteed to keep you out of trouble every time.
It's all case-by-case.
 
> 2. If someone implements a processor compatible with the instruction set
> of another processor but without copying anything else from that
> original processor apart from the original instruction set, will that be
> patent infringement?

If you infringe on the claims contained within someone else's patent,
it doesn't matter whether you developed independently.  And as far as
working from the instruction set goes, watch for copyright as well.
Some manufacturers copyrighted their mnemonics in an effort to control
knock-offs.

I think there's a lot to be said for common sense, though.  A patent
holder is probably not going to come after you hammer & tongs if the
subject of the alleged infringment is a patent that, though still 
valid and enforceable, is no longer of primary commercial interest to
the holder.  And if you develop independently, you've exhibited good
faith, which is a major factor.

In any event, nobody brings down a suit without first alerting you to
the fact that you've infringed their rights and giving you a reasonable
opportunity to mend your ways.

Jonathan