I had the idea to connect a game boy link cable port to the gpio pins, so that i can build up a link-cable connecton between an original gameboy and the emulator. The hardware shouldn't be a problem, but software is giving me some problems.
I lookt into the game boy programming manual (http://www.chrisantonellis.com/files/gameboy/gb-programming-manual.pdf) and the source code of the tgbdual emulator (https://github.com/libretro/tgbdual-libretro) and i think i know what changes i have to make and i figured out how to recompile the code into a ".so"-file.

Here comes the problem: i don't know how to implement this .so file into my recalbox system and choose it as standart gb emulator.

i hope some of you can help me with that.