The named pins feature for supporting external pins requires the definition of machine_pin_ext_init and various other functions for configuring, setting and getting external pins.

This feature is entirely monopolized by the Pico W build, in such a way that it's impossible to add additional external pins on top of those defined for Pico W.

There should be no reason why we can't take a copy of machine_pin_cyw43.c , and extend it as necessary.

This would require moving the hard-coded exception for Pico W in CMakeLists.txt into the board config -

https://github.com/micropython/micropython/blob/3637252b7bc3e85ea92038161e008a550991d1f4/ports/rp2/CMakeLists.txt#L300-L302

ESP32 handles additional sources with the MICROPY_SOURCE_BOARD variable, I think the RP2 port should mirror this behavior, and this is how machine_pin_cyw43.c should be included - https://github.com/micropython/micropython/blob/3637252b7bc3e85ea92038161e008a550991d1f4/ports/esp32/esp32_common.cmake#L105