Rust Firmware Experiments for the Sipeed Longan Nano

Some code to test out ideas and projects using embedded Rust on the Longan Nano

Setup

• stm32flash
• riscv32-elf-objcopy
• longan-nano
• Rust 1.51+

Building

Install (or update) the riscv32imac-unknown-none-elf target:

rustup target add riscv32imac-unknown-none-elf

Then run the release build for the project:

$ cargo build --release

which produces the firmware binary (cross-compiled to riscv32imac-unknown-none-elf target).

Next, to create the raw firmware binary using objcopy from riscv32 binutils:

$ riscv32-elf-objcopy -O binary target/riscv32imac-unknown-elf/release/<project-name> firmware.bin

where <project-name> is replaced with the name of the crate.

Flashing over other protocols

• dfu-util: https://github.com/riscv-rust/longan-nano#using-dfu-util-for-flashing
• openocd: https://github.com/riscv-rust/longan-nano#using-openocd-for-flashing-and-debugging
• rv-link: https://github.com/riscv-rust/longan-nano#using-rv-link-for-flashing-and-debugging
• serial: https://github.com/riscv-rust/longan-nano#using-serial-for-flashing

Troubleshooting

If there is an error when flashing the Longan Nano, check if the device is in DFU-mode, and that /dev/ttyUSB0 is writeable by the current user (or run stm32flash as root).

To enter DFU-mode:

• press and hold the BOOT0 button
• press and release the RESET button
• release the BOOT0 button

or

• press and hold the BOOT0 button while device is off
• power on the device
• release the BOOT0 button

Then, retry flashing the device.