You can patent something like "any possible hardware circuit that implements [the functionality of some weird yet mandatory ARM instruction]". The patent doesn't cover emulators because they're not hardware.

Way back in the day there were some MIPS patents that only covered a few instructions so people would build not-quite-MIPS clone CPUs without paying any royalties.

thanks for the hint. i found https://www.probell.com/lexra/

sheesh, patent https://patents.google.com/patent/US4814976A/en is a real "gem"

but its probably a good example: faulty patent (later invalidated) to do something obvious

MIPS sues a company that doesn't even implement the odd instructions because it traps them, allowing a possibility of emulation.

there's literally no case here

just to sue them into oblivion and squish them with superior cash resources. and then to get squished by ARM because they weren't paying attention.

it's like a dark fairy tale. i hate corporate lawyers.

Thanks for highlighting Lexra, my first startup. After becoming a patent agent and strategist 15 years later, these are my takeaways.

1. Little companies don't sue big companies. No need. Startups exist because they have something new and move faster. 2. Big companies don't sue little companies. Too little money, it would look anticompetitive to the gov't, and most startups fail, anyway. 3. Medium companies sue little companies when they start taking away prime customers.

ARM sued Picoturbo and they settled. Lexra chose to fight MIPS. Lexra and MIPS hurt each other. That gave ARM the opportunity to dominate the industry.

On an unrelated topic, readers looking for concise basic info on patenting that your attorney might not mention might enjoy. https://www.probell.com/patents

That is what was done with the THUMB instructions. IIRC

Are there remaining patents relative to arm architecture that haven't expired already?

For ARM7TDMI probably no, but for the A, R and M cores, for sure there is. That is the name of the game.