[Gladdyu]

The issue was that there wasn't a cheap riscv board that supported the privileged section of the ISA (so you can run an OS on it). This, being a microcontroller, doesn't either.

[freeopinion]

The Reference Manual claims "Machine (M) and User (U) Privilege levels support" on page 22.

Probably not the kind of privileges discussed yesterday.

[Taniwha]

yup, for linux you want M/S/U modes at least (kernel runs in S) and page table table support of course

[p0llard]

I was under the impression you could get away with using Machine mode for both the SBI and the Kernel?

Sv39 paging is the major requirement as you point out.

[Taniwha]

Machine mode runs without the MMU, linux really needs an MMU to do kernel stuff too (including stuff like copyin/copyout)

[nickik]

There is actually quite a bit of work going on in Linux without MMU. Check Linux Plummers conference RISC-V track for example.

[Taniwha]

Yeah that's why I said "really needs", there are cut down versions that will run without an MMU, it's not really the mainline Linux though - I've worked with MMUless kernels in the past, it's not a lot of fun (and I started porting V6/V7 for base and bounds swapping machines)

[p0llard]

Ah, I didn't actually know this, thanks for pointing it out :)