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Comment by sneak | Hacker News Reader

Technical question: why do people need ARM licenses? Surely you don't need anything from them to design a chip from scratch that implements the same instruction set, as Cyrix and AMD famously did to the ia32.

Are the licensees using parts of the actual chip design? Are their own designs too far down the "derivative work" rabbit hole due to not being cleanroomed that they have no hope of ever not licensing?

What are the specifics?

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The ISA isn't very useful IMO, outside of the compiler framework.

The crux of modern chip design is the tradeoff in MHz, peculiarities of Tomasulo's Algorithm (out of order buffers, tuning sizes and number of pipelines, etc. etc.).

Lets take an example: should you have 200 64-bit words in the reorder buffer, or should you have 800 (Apple M2). What's the tradeoffs? How much slower does accessing the reorder buffer get when you need to go from 8-bits to 10-bits to address the various locations?

How many multiplication units should you have? I know Intel has 3 of them per core, is that enough? Or do you go IBM Power route and go for like 20 pipelines wide?

Etc. etc. etc.

ARM Neoverse N2 makes a lot of these decisions, packages them up into an easy moniker ("General Purpose"), and also has customizations towards V-cores (higher performance but bigger) vs E-cores (lower-performance but smaller and more power-efficient).

You then make decisions based off of the core as a whole, rather than designing a core. Ex: do you use 128kB of L1 cache? Or 64kB? Do you do L1 / L2 / L3 cache like Intel? Or do you do L1 / L2 cache like Apple?

You still need to make these "uncore" decisions, including the important MESI (core-to-core communications: Modified data vs Exclusive data vs Shared data vs Invalid data). Even _IF_ you buy an off-the-shelf core like Neoverse N2, you're no where close to finishing an actual chip yet cause the darn thing can't even talk to RAM yet.

ARM uses a mix patents, copyright and trade secret protections for their ISA. The give you the RTL/vhdl/verilog for the core when you license it and they forbid you from changing the core in the license agreement to use it.

You can clean room implement the trade secret part, but the patents would be an issue and ARM could still sue and drag things out.

You also could never legally call it ARM because it's trademarked. This makes it harder for semiconductor vendors to sell chips.

See the Qualcomm lawsuit shitshow which is now causing Qualcomm to invest big in RISCV.

Chip IP is usually encrypted verilog. Your EDA tools compile it in a secure enclave, basically. You have no real options to modify it.

Well, encrypted OASIS these days for something like a higher perf CPU core, but close enough for the point you were making.

Yeah, for hard layouts that the vendor has already done, that is true. Either way, it's transferred encrypted and protected so you can't screw with it.

You also don't need anything from your architect to design a building from scratch. But unless you're an architect yourself, it's going to be prohibitively difficult, or even impossible. So people hire architects.

> Surely you don't need anything from them to design a chip from scratch that implements the same instruction set, as Cyrix and AMD famously did to the ia32.

Cyrix and AMD had licenses to do so, ultimately deriving from a time when Intel needed second sources of their CPUs in order to win defense contracts.

Cyrix and AMD licensed tech from Intel back then.

Interesting, I didn't know that. Why would Intel do that?

What is the legal interpretation of IP law that says you need permission to design a chip that implements an ISA?

Intel licensed x86 to provide a credible second source, which they needed for some of their early business deals.

For AMD the primary driver was IBM.

In order to get the contract for the IBM PC, Intel had to agree to have a second-source manufacturer for their CPUs. Intel already had a relationship with AMD so it made sense to use them.

Patents, lots of patents. A lot of them are expired. By now you could make an 80486 and I guess also a Pentium clone without worrying about patents. But there can also be patents on how you make something performant on modern silicon, so it's not only about the ISA.

Originally Cyrix did not license from Intel. Intel sued for patent infringement and lost badly enough they had to give Cyrix a few million to settle their counter claims.

Cyrix has also sued Intel over their Pentium chips. In the end the results of all the lawsuits are cross-licensing deals.

Only a few licensees are capable of designing their own core from scratch. Most customers are licensing some form of reference design.

> Surely you don't need anything from them to design a chip from scratch that implements the same instruction set, as Cyrix and AMD famously did to the ia32.

Cyrix and AMD got (cross-)licenses from Intel:

* https://www.sec.gov/Archives/edgar/data/2488/000119312509236...

* https://www.kitguru.net/components/cpu/anton-shilov/amd-clar...

This has been true since the very beginning:

> Early 1980s--IBM chooses Intel's so-called x86 chip architecture and the DOS software operating system built by Microsoft. To avoid overdependence on Intel as its sole source of chips, IBM demands that Intel finds it a second supplier.

* https://www.cnet.com/tech/tech-industry/intel-and-amd-a-long...

* https://jolt.law.harvard.edu/digest/intel-and-the-x86-archit...

The reverse engineering happened with Compaq doing the BIOS:

* https://www.allaboutcircuits.com/news/how-compaqs-clone-comp...

This was a major plot point in AMC's (very good) show Halt and Catch Fire:

* https://www.internethistorypodcast.com/2014/05/the-incredibl...

* https://arstechnica.com/gaming/2014/05/review-halt-and-catch...

* https://en.wikipedia.org/wiki/Halt_and_Catch_Fire_(TV_series...

Making and more importantly verifying a high performance CPU is extremely hard. AMD has taken a lifetime to get where it is.

People don't want to design chips from scratch. ARM gives you a lot of working stuff to bootstrap a product.

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