[sitkack]

smaller instruction set, Arm has grown, reference manual is over 6k pages

smaller easier to read specs

easier to get new features ratified, org is a steward, isn't seeking rents

easy to add custom instructions

lots of OSH implementations to choose from

large 3rd party ecosystem, IP, compilers, OS, etc.

[cestith]

To be fair, even with a closed ecosystem for the cores themselves there is a large third party ecosystem in compilers, OSes, support hardware, and documentation around ARM these days. It's interesting how quickly all of that popped up around RISC-V the past few years though. ARM has had decades getting where they are with the ecosystem around their cores.

[sitkack]

It did take decades to get here only because it took millions of years of humanity to get here. We are in a much different space right now, RISC-V benefits from all those years and decades and will naturally reach and surpass parity with all other chips, not just Arm.

RISC-V is basically a different encoding to achieve the same computation as being done on Arm. From far enough out and that isn't very far they are identical. Putting a RISC-V front end on an Arm chip is not difficult. Refactoring Arm tooling to support RISC-V is just engineering work. Every program fixed to run on Arm's memory model, now runs on RISC-V as well. RISC-V is a catamaran zipping around on Arm's moat.

We see the same thing with languages and frameworks. Innovation is accelerating.

[cestith]

There's a big difference in support for RISC-V and for, say, POWER (which has new processors in the line), Sparc, or Loongson (which is a new family of processors with roots in MIPS) which are all based around open architectures. You can restate the idea of Turing equivalence all you want, but that alone does not explain why one processor captures a bunch of human effort around it while others do not.

Part of that I think is Patterson and Hennessy writing one of the most standard books in the field and then turning it into its own ISA, which has in fact taken decades of their effort.

LLVM is a great tool, yes. There's a bigger body of research now than in 1985 or so, of course. But we had pcode before we had LLVM IR, and we had compile-to-C for a lot of languages in between. If you really think the only difference is some Kurzweilian inevitable march toward technological perfection over time and it has nothing to do with the tools being open and of high quality then I don't know what to tell you to dissuade you from that faith.

[rrss]

Smaller instruction set and shorter reference manual aren’t necessarily good attributes. The risc-v reference manual is short because in part because it is has terse-to-vague descriptions of things (not great for a specification) and because the ARM ARM specifies a bunch of things which are omitted from the RISC-V architecture spec, which either implementors will have to design themselves or the RISC-V org will eventually add in a revision or extension spec (e.g. Zicbom, Zicboz, Zicbop)