I recently bought a Raspberry Pi Pico to play with, and am attempting to upload my first program to it the Arduino way, as my own operating system rather than a c++ program over an existing operating system (meaning to replace the built-in Raspberry Pi Pico operating system which runs MicroPython, not in the sense of running Linux, Windows, Mac, or any derivative or fork). I have not found any record of people hacking it like that - is it possible? If so, how would I go about it? Sorry if this is in the wrong Stack Exchange.
Apparently there's official support for it, now anyway.
pico.name=Raspberry Pi Pico
Unfortunately, I don't have any way to give it a proper test as I don't have one of these. But I did go so far as to install the core and compile a simple hello world program.
In boards manager
Search for "mbed rp2040"; these names sometimes change, but those terms work well now. You can see in the lower item, I have version 2.0.0 installed.
Board menu selection
Arduino Mbed OS RP2040/
Raspberry Pi Pico
Seems to work.
As you see it at least builds without error. As I said, I'm unable to give it a real test. But that at least looks promising.
Here is the library for the Arduino IDE and a Raspberry Pi pico.
Just install normally as a .zip.