Flashing the Rust Firmware into Raspberry Pi Pico

After building our program, we’ll have an ELF binary file ready to flash.

For a debug build (cargo build), you’ll find the file here:

./target/thumbv6m-none-eabi/debug/pico-from-scratch

For a release build (cargo build --release), you’ll find it here:

./target/thumbv6m-none-eabi/release/pico-from-scratch

To load our program onto the Pico, we’ll use a tool called Picotool. Here’s the command to flash our program:

#![allow(unused)]
fn main() {
picotool load -u -v -x -t elf ./target/thumbv6m-none-eabi/debug/pico-from-scratch
}

Here’s what each flag does:

• -u for update mode (only writes what’s changed)
• -v to verify everything wrote correctly
• -x to run the program immediately after loading
• -t elf tells picotool we’re using an ELF file

cargo run command

Typing that long command every time gets tedious. Let’s simplify it by updating the “.cargo/config.toml” file. We can configure Cargo to automatically use picotool when we run cargo run:

[target.thumbv6m-none-eabi]
runner = "picotool load -u -v -x -t elf"

Now, you can just type:

cargo run --release

#or

cargo run

and your program will be flashed and executed on the Pico.

But at this point, it still won’t actually flash. We’re missing one important step.