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It's not clear to me that raw ISAs can be copyrighted or patented. Worst case there is clean room reverse engineering. Emulators are legal.
by btrask 8y ago
It's not clear to me that raw ISAs can be copyrighted or patented. Worst case there is clean room reverse engineering. Emulators are legal.
- earenndil 8y agoAFAIK intel threatened to sue someone who was implementing an x86 emulator on top of an arm chip. I think emulators are legal because they're not in hardware and so not infringing on intel's market space?
- nickik 8y agoIt might not be clear to you but it is very clear to Intel and ARM.
- brandmeyer 8y agoThere are tons of patents out there for the circuits which efficiently implement some instructions. Most of those patents have expired by now, but new ones pop up every once in a while. One recent example would be the circuit which computes steering bits for implementing pext and pdep on a butterfly network. There are also plenty of patents for particular descriptions of instructions. They may be fairly narrow in scope, depending on how close they are to prior art. But they don't have to be particularly wide in scope in order to prevent cloning. It would not surprise me at all if the x86's encoding choice for `reg + reg * scale + displacement` was patented. Emulators can absolutely require licenses. The ARM emulator shipped with Android for x86 is licensed by ARM, for example. While there aren't very many (uh, any at all?) x86 phones, x86 Chromebooks with Android support is a thing.