It's been a while since my last project log. In the mean time, I have successfully used my PCB edge connector/breakout and Sven Köhler's PokeDuino project to generate some cool pocket monsters for my Pokémon Yellow game. I really like the simplicity of this project. The embedded hardware is a mere "gateway" transferring data from the serial connection to the GameBoy link cable and vice versa.
As mentioned in the comment/discussion section of this project, the board edge connector (a.k.a. the breakout PCB) I designed previously wasn't perfect and I would recommend using a replacement connector for the GameBoy Advance, since these can be found on AliExpress for less than 0.20 EUR a piece.
I figured, since I would be using this connector for my project, it would be interested to search more information about the protocols used by GameBoy Advance games. Unfortunately I have not yet found the information I was hoping to find. However, I did find the Catskull Electronics website that linked to an EAGLE library containing a design for the GBA link connector.
As you might have also read in the discussion section, I already designed my own EAGLE part for the connector, but I was still working on fine tuning it. The library I found is already used for products sold by Catskull, so it is already verified by them. Guess I'll be throwing my own work in the bin.
I'm currently in the process of designing an initial USB-to-GameBoy-Link adapter PCB. I'm planning on using an STM32F103C8T6, which is an ARM microprocessor. It is way more powerful than what I need, but they are inexpensive and have USB connectivity built-in. This makes them even more interesting to use than an ATmega328 for example.
I'll try to keep you posted about my progress!