Linux on a $0.15 RISC-V microcontroller
This project enables the CH32V003 microcontroller to run Linux. It achieves this by using an 8 megabyte SPI PSRAM chip and a RISC-V emulator (the very nice mini-rv32ima by cnlohr). The emulation is needed because the PSRAM cannot be mapped into the address space of the microcontroler. The Linux kernel and rootfs is loaded into PSRAM at boot from an SD card. FAT filesystem access is provided by the Petit FatFs library.
This project uses the ch32v003fun SDK, which must reside in the same folder where this repository was cloned.
The PSRAM and SD card are connected to the hardware SPI interface of the CH32V003. The chip select pins can be set in the thing_config.h file. The console can be accessed over the UART pins. The SD card containing the Linux image file must be formatted as FAT32 or FAT16, and the file must be placed in the root.
A suggested schematic and corresponding single-layer PCB design can be found in the hardware folder (it's a KiCad 7 project).
Boot time is around 5 minutes. The Linux image includes the coremark benchmark in the /root/ folder.
If you wish to build your own Linux image, you can do so by running make linux. The resulting image will be located in linux/buildroot/output/images/.