[Improvement] Template support for quick development via USB (BOOTSEL)

[migueleliasweb]

Hi all,

I'm a bit new to rust and no_std embedded development.

I have recently stumbled across the fact that one would need to constantly reconnect the rp2350 (or any Pico for this matter) and hold BOOTSEL in order for the flashing via PICOTOOL to work. Otherwise a message such as No accessible RP-series devices in BOOTSEL mode were found. is shown. This gets a bit tedious and slows downs the dev process substantially.

I did a bit of research and it seems that there is a way for the flashed firmware to play nice with USB via some kind of code that automatically puts the Pico into a mode that allows new code to be flashed directly via the USB interface without basically "resetting" the device (when pressing BOOTSEL). This means the user would have to press BOOTSEL once and as long as the firmware is not horribly crashing inside the MCU, they would be able to re-flash it without pressing the button and reconnecting the Pico.

As the Raspberry Pi foundation and the community want to lower the barrier to entry for projects using the Pico, would it make sense to incorportate this code onto the rust templates to simplify and speed up the development process?

I believe this is related to:

• https://github.com/raspberrypi/picotool?tab=readme-ov-file#forced-reboots
• https://github.com/raspberrypi/pico-examples/tree/master/hello_world/usb
• https://github.com/rp-rs/rp-hal/blob/main/rp235x-hal-examples/src/bin/usb.rs (using usb)
• https://github.com/rp-rs/rp-hal/blob/main/rp235x-hal-examples/src/bin/uart_loopback.rs#L392C4-L398C7 (calling reboot from code)

Thanks in advance.

[memark]

I haven't looked into this (though it appears interesting!), but I can really recommend the Raspberry Pi debug probe. It's pretty cheap and really good. (You can also use a second Pi Pico with a bit more wiring.)

[migueleliasweb]

Hi @memark , I definitely saw this!

It looks interesting indeed! As I'm progressing more into no_std Rust (bare with me I come from a high-level Go background), I'm considering getting a probe to streamline my dev flow for microcontrollers.

The reason I'm trying to tackle this from the software perspective is that requiring an external probe incrases the barrier to entry. Especially when someome is getting started and they buy their first pico and all of a sudden they realise they "can't get a nice dev flow unless they have to buy yet another thing"...it's a bit meh. I hope that makes sense.

[memark]

I hear you. It's not a huge hustle though, I spend my first few months manually disconnecting and reconnecting the USB cable for every flash. (It's much easier on the computer side than on the Pico.) Then I used a second Pico for the probe. Then I bought the ready-made one.

That said, I like the idea!
I also found this, which contains the code for booting into BootSel mode (in the form of a panic handler):
https://github.com/jannic/rp2040-panic-usb-boot

If that could be combined with being triggered by just pressing the BootSel button, we would be home I think.

Edit: I saw now that one your examples already provided a way to reboot into BootSel as well.