I've been toying with the idea of adding Super Gameboy support to Metroid 2, but I'm not entirely how to go about it. Reading some documentation about it says that you have to transfer packets of data and it's initiated by writing data to specific points of the joypad register.
A command packet transfer must be initiated by setting both P14 and P15 to LOW, this will reset and start the SNES packet receiving program. Data is then transferred (LSB first), setting P14=LOW will indicate a "0" bit, and setting P15=LOW will indicate a "1" bit.
What would that code actually look like? I've only done a little bit of assembly for a class and I'm not sure how to even write data to that area.