Comment by dmitrygr

14 hours ago

For anyone else curious: custom FPGA-based CPU code but not a custom architecture. This is an RV32I core. The article takes along time to give up this fact.

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dmitrygr

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kryptiskt  13 hours ago

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.

  • Dylan16807  12 hours ago

    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.

  • voidUpdate  13 hours ago

    It's a custom implementation of an existing architecture

    • ahartmetz  11 hours ago

      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".

    • speed_spread  9 hours ago

      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.

      2 replies →

  • dmitrygr  12 hours ago

    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.

zuzululu  14 hours ago

thanks for saving me the time but it is pretty cool to see i'd love to learn more about fpga my goal is to run very old rare consoles