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Comment by kryptiskt | Hacker News Reader

Deciding on an ISA like RV32I only sets constraints on your architecture, it doesn't give you any of it for free. So I think it's entirely valid to say that it's a custom architecture if they didn't use any pre-existing CPU design.

Basically, they had the API interface and implemented everything behind it. I think saying that "it's an RV32I core" vastly underrates the design work that goes into actually implementing an RV32I core from scratch.

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Making a particularly good core is hard. Making a core to the minimum risc-v spec is what you do in a single college course. It's what the ISA was designed for.

The *architecture* is RV32I_Zmmul which is unambiguously neither new nor custom.

What you describe (the specific implementation details of a core) is *microarchitecture*. In this case clearly a lot of work was done and it is cool, but the *architecture* is indeed RV32I and not custom

I was not undermining anything. I was helping others find the info I sought and took a while to find. This is why i left my comment. Everyone has their own interests. As an example, my thoughts were "whoa... a new architecture... did they write a new compiler or rewrite doom in assembly?" and for that "it is rv32i" would have been a quick answer.

It's a custom implementation of an existing architecture

It's common to call the instruction set just "architecture", or ISA (instruction set architecture) to be more precise. The implementation is commonly called "microarchitecture".

RV32I doesn't define any architecture, it's just an ISA i.e. a software contract that happens to be implementable in hardware. The CPU could run on outer space goop and still be RV32I.

"RV32I doesn't define any architecture, it's just an ISA."

My friend...

You are right, 'A' stands for Architecture. _Instruction Set_ Architecture that is. Not CPU architecture. I should have been more clear:

> RV32I doesn't define the hardware architecture

FTFM - satisfied?

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