pico_examples VS notcursesada

I'm having issues connecting the WS2812B with Raspberry Pi Pico. I'm trying to execute the example program https://github.com/JeremyGrosser/pico_examples/blob/master/ws2812_demo/src/main.adb

It'll all be open source eventually, but for now I've just released my driver libraries and some examples. https://github.com/JeremyGrosser/pico_examples

* Is there a way to declare data layouts to have compatibility with C, similar to #[repr(C)] in rust?

Yes, and if you have a C header file, gcc can even translate most struct definitions for you. Here's an example of a "thin" binding generated that way: https://github.com/JeremyGrosser/notcursesada/blob/master/sr...

* Is there a way to catch C++ exceptions?

Yes. https://www.adacore.com/gems/gem-114-ada-and-c-exceptions

* Is there a way to catch C longjmps()?

By default, the GNAT runtime uses setjmp/longjmp to implement exceptions. I'm not sure how you'd connect that to a C library's setjmp though.

* Is there a way to have some kind of custom control over ABI issues, e.g. define custom FFIs to langauges with a different ABI? Or anything close to this? For that matter, does any language have something like this or does it not make sense?

ABIs are selected with the Convention aspect. Conventions are implementation defined and would require patches to the compiler to add new ones. GNAT currently supports Assembler, C, CPP, COBOL, and Fortran calling conventions.