linux.md

Booting Linux on biRISC-V

The core currently implements RV32IM + machine/supervisor/user mode and has basic MMU support.
The mainline Linux kernel requires RV-A (atomics) instruction support (this is a future planned feature for biRISC-V).

Atomic instruction support can be emulated with a machine mode bootloader (with a performance penalty), allowing unmodified Linux kernel and userspace images to be used.
This currently allows biRISC-V to successfully boot Linux to userspace.

Required SW components

• riscv-linux-boot (SBI bootloader) - https://github.com/ultraembedded/riscv-linux-boot
• Prebuilt Kernel images - https://github.com/ultraembedded/riscv-linux-prebuilt

Required HW components

• biRISC-V configured to run Linux (see configuration guide)
• 32MB+ SDRAM/DDR available @ 0x80000000
• Xilinx UART-Lite accessible @ 0x92000000

Building combined kernel + bootloader

cd riscv-linux-boot
make LINUX_DIR=/path/to/riscv-linux-prebuilt VMLINUX=/path/to/riscv-linux-prebuilt/kernel/vmlinux-rv32ima-5.0 DTS_FILE=/path/to/riscv-linux-prebuilt/dts/config32.dts

Example Output

Running on a Digilent Arty Artix 7 (35T);