Hacker News Reader

Comment by rowanG077 | Hacker News Reader

The Readme doesn't answer it but I struggle to see why you want a c implementation of an ISA.

Not sure if this was intended, but coming to this as someone vaguely aware of RISC-V, it's looking like a fantastic form of documentation for the ISA, that both describes and gives a way to play with it, but in an intuitive, even fun manner.

Obviously this works best for someone who already knows C - but, given it's C89 mitigates against this aspect somewhat.

A reference implementation would be in Verilog or VHDL.

So you can compile and run it on any platform with a C compiler

That is just something you can do with C code. That is not a goal in itself. Why would you want to run a C ISA instead of just using a standard simulator? Why not use verilator + any of the open source RISC-V cores?

Because those are slower, more complex, and more difficult to understand?

I doubt verilator is much slower. The speed of it is insane. They are indeed more complex and difficult to understand. But I fail to see how that is a criterium. I would very much rather include an industry standard library in comparison to something homegrown.

> They are indeed more complex and difficult to understand. But I fail to see how that is a criterium.

It's... not? Like, if you want to merely use an ISA, you don't need it to be simple or easy to understand, in fact tons of people pride themselves on making extremely high-performance RISC-V cores with OoOE and so on.

But the reason why someone might want a C implementation of an ISA is different from the reason people might want to go implement an ISA in a real project: maybe they want a software simulator that is easy to understand for one reason or another, perhaps for learning or demonstration purposes, or just as a fun hobby project.

These people wouldn't benefit from just pulling down Verilator or using one of the existing BATTLE-TESTED INDUSTRY-STANDARD PROFESSIONALLY-AUDITED HIGH-PERFORMANCE implementations because they literally don't care about any of those things.

In any case, it's a fallacy to assume that every programming project out there has to address a need in order to have a place. https://justforfunnoreally.dev

Yes a hobby/learning is a great reason, why not just start with that? I was simply wondering what the reason was. Maybe the author had an interesting need for a C implementation to do something. Me asking for the reason is not me saying it doesn't deserve to exist. I don't think you are arguing in good faith here.

> why not just start with that?

I'm not the one who started the thread.

> I don't think you are arguing in good faith here.

With that, this discussion is over.

Considering it's allocation-free, maybe it's an ultralight/ simulator for checking large quantities of compiler output? (i.e no VM to create and destroy for every testcase)

Or the same but for testing some verilog/vhdl CPU implemetation in a simulator?

Or since it's only 500SLOC, maybe it's just for fun!

This is an excellent idea. One limitation of a testing library of mine, `mptest`, is its inability to sandbox tests. I may take this idea and develop a more robust (and potentially parallel) testing framework around it.

Then I would expect a comparison with verilator.

Perhaps this could be used to run sandboxed code. Game engines could safely run mods using something like this, ala QuakeC.

For modern game engine you most likely want WebAssembly support. e.g. Flight Simulator does that https://flightsimulator.zendesk.com/hc/en-us/articles/766290...

Sure, I’d love to see your 600 line webassembly interpreter.

Run wasm on this core.

Definitely. My motivation for writing this was to have a simple CPU for a virtual game console-like project. I decided to release it on its own, though.

Reply on news.ycombinator.com