Support the NOMMU port

[mithro]

According to Palmer;

The NOMMU RISC-V port was posted to the Linux Kernel mailing list just this week

I think he is talking about the stuff at https://github.com/chmmn/riscv-uclinux

It would be good to support NOMMU Linux on LiteX for even lower resource usage (and more predictable performance).

[mithro]

@Dolu1990 - FYI How many resources would not having a MMU save?

[Dolu1990]

@mithro I will check.
But also, wasn't it also about only having a machine mode only + no mmu linux port ?
That would probabably save much :D

[Dolu1990]

I would say, it would mainly make it usable in a ice40 8K
Currently, i have a Linux SoC with SDRAM which can hold in it, but that's realy full

[mithro]

@Dolu1990 That would be awesome!

[futaris]

https://lwn.net/Articles/790888/

[futaris]

NB, this doesn't support shared libraries. Static executables only.

[AnttiLukats]

it would also make it able to run in MAX10 10M08 device, and maybe maybe maybe in 8Mbyte HyperRAM,,, for many years ago running nommu in 4Mbyte was not a problem

[enjoy-digital]

Except doing it for the challenge, I'm not sure to see a real use case for this: iCE40 are good for pure logic gateware or to embeds small CPUs running bare-metal apps or small RT OSes, not to run Linux. Medium size FPGAs (ECP5, Cyclone4/5, Artix7, etc...) easily integrate the current Linux VexRiscv SoC so I'm not sure it's worth putting much efforts in a NOMMU port (but if anyone do it, that would be nice to share this work with us).

[disdi]

Now buildroot root supports NoMMU riscv32 qemu.
RP2350 support also exists.

I think it will be very useful to have NoMMU linux running on Vexriscv Linux generated without MMU plugin.