Based on https://github.com/ch32-rs/ch32v203-demo/
At the moment this needs a custom rust toolchain that supports RV32EC.
cargo build -Zbuild-std=core --release
riscv64-unknown-elf-objcopy -O binary target/riscv32i-unknown-none-elf/release/ch32v203-rust-blink ch32v003-rust-blink.bin
minichlink -w ch32v003-rust-blink.bin flash
minichlink -b