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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Dylan16807 9 hours ago | parent | next [-]

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.

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voidUpdate 10 hours ago | parent | prev | next [-]

It's a custom implementation of an existing architecture

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ahartmetz 8 hours ago | parent | next [-]

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".

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speed_spread 7 hours ago | parent | prev [-]

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.

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Brian_K_White 3 hours ago | parent [-]

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

My friend...

	▲	speed_spread an hour ago \| parent [-]
		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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dmitrygr 10 hours ago | parent | prev [-]

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.