pico_enable_stdio_usb

[mark2b]

Using pico_sdk for cpp, there is feature to enable USB stdio in the MakeLists.txt pico_enable_stdio_usb(${NAME} 1) It allows use picotool not in BOOTSEL mode Is rp-hal has similar feature?

[ithinuel]

Hi,

If my understanding is correct, this CMake function enables the use of a usb CDC as the std in/out (printf).

When this is enabled, a side effect by default is also to add a class vendor specific interface (implemented here) that allows a program on the host to trigger a reset to usb boot.

Picotools searches for this interface and ignores the others, so you don't need the first ones to be CDC (it could even be the only usb interface present on the device).

I don't think such a feature belongs to the rp-hal per se (as it would require to setup the usb peripheral and to poll the usb stack in the application anyways) but it could definitely be implemented as a separate crate implementing the vendor specific UsbClass to behave like the sdk version does. I don't know if anyone ever tried to do that.

[romainreignier]

I was looking for the same feature and I have seen that @ithinuel has worked on it: https://github.com/ithinuel/usbd-picotool-reset

Tested with picotool info -f -a, the device effectively reboots into BOOTSEL mode but might take too much time because picotool does not detect it soon enough:

$ picotool info -f -a
Tracking device serial number TEST for reboot
The device was asked to reboot into BOOTSEL mode so the command can be executed.

Despite the reboot attempt, no accessible RP2040/RP2350 devices in BOOTSEL mode were found. It is possible the device is not responding, and will have to be
manually entered into BOOTSEL mode.

But the device is indeed in BOOTSEL mode:

$ picotool info -a
Program Information
 none

Fixed Pin Information
 none

Build Information
 none

Device Information
 type:        RP2040
 revision:    B1
 flash size:  2048K
 flash id:    0xE66118604B286D24

And we can reboot it back to application code with:

picotool boot -a