How to Build & Run Linux on Kendryte K210 RISC-V NOMMU Processor

A few months ago, we wrote that Western Digital was working on Linux & BusyBox RISC-V NOMMU, and managed to boot a minimal Linux OS on Kendryte K210 powered Sipeed Maix Go board.

RISC-V NOMMU support was scheduled for Linux 5.5, and now that the new kernel has been released, Damien Le Moal has pushed the code allowing to build Linux and a busybox based roofs for RISC-V 64-bit NOMMU platforms using buildroot.

RISCV64 NOMMU Menuconfig

I could start the build following the instructions on Github, but it failed as a Linux 5.6 RC1 tarball was missing. But I noticed “Vowstart” picked up on Damien’s work, and wrote detailed instructions. So let’s try the build out using a machine running Ubuntu 18.04.

We’ll have to make sure dependencies are installed first:

Then we can retrieve the source code and do some preparations (e.g. extract Linux 5.6 RC1 tarball):

The next step is to build the toolchain. It will take a long while because there’s a lot of code to build and download from the Internet:

This ended successfully with:

We can now install the RISCV64 toolchain which will use for cross-compilation:

Next up is buildroot build for Kendryte K210 NOMMU processor:

The last step copies the file into $PROJ_ROOT/rootfs_k210 folder.

They also decided to build the Tiny C Compiler in order to be able to build code on the board itself. It’s not really necessary, as on such low-end hardware most people would likely prefer to cross-compile their code instead, but let’s go ahead anyway:

They also made a script to setup and copy k210 rootfs CPIO image into linux-kernel/k210.cpio.

We can now finally build the Linux 5.6-RC1 kernel:

I don’t have a Sipeed MAIX board on hand, so I have not tried that part, but you can flash the resulting image as follows assuming your board is connected over /dev/ttyUSB:

The first two lines are to add the current user to dialout group to get access to /dev/ttyUSB0 without having to be root. The third one installs kflash utility, followed by the command that does dump the image to the internal flash, and the last one is to get terminal access to the board.

Kendryte K210 Linux

That means you can now run Linux on low-cost RISC-V hardware such as the Sipeed MAIX Bit sold for around $14 and up. Note that’s technically uCLinux, you’d have to work with just 8MB RAM and handle stack overflow issues commonly experienced in processors without a memory management unit.

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