I think CBinding.jl could be helpful if one wanted to write a target-specific shim library in C and link against it. I would expect that some of the glue is going to be easier to write in C than in Julia, and you can play some tricks with macros to create bare modules [1] within some kind of `@arduino_setup`/`@arduino_loop`-style blocks.

Edit: By the way, those target-specific shims might already exist as part of the Arduino IDE. PlatformIO [2] is also another possible collider of these types of platform-specific glues.

[1]: https://docs.julialang.org/en/v1/manual/modules/#Default-top...

[2]: https://docs.platformio.org/en/latest/boards/index.html