Build Firmware Reference:

https://datasheets.raspberrypi.org/pico/raspberry-pi-pico-python-sdk.pdf
https://peppe8o.com/compile-micropython-firmware-raspberry-pi-pico/
https://github.com/orgs/micropython/discussions/9627#discussioncomment-3883905


Custom Board Sources:

YD-RP2040 = https://github.com/micropython/micropython/pull/12281/files
LITE PURPLE = https://github.com/sav-lab/LITE_PURPLE_16MB