So I'm undertaking a huge (maybe? at least a lot to learn for me) project. I'm trying to create an input viewer for GBA SP or Game Boy Player. I've tried to read from my GC Controller Data Line with an Arduino and am able to read it fine until the Game Boy Player is booted, since the GC is now issuing Joy Bus commands for the GBA. I've tried to read the SO, SC, and SD lines while I had my SP connected to my GC with GBP running and haven't been able to get a good read. So now I'm trying to find as much documentation as possible for pretty much every route I can take. IIRC when in Joy Bus Mode, when issued a data read command, the GBA responds with 5 8-bit packets of data, but I haven't been able to find anything on how to interpret this data. I don't think I've got the right timing down to read the data at the moment. Or if I can find a way to distinguish the data read command going to SI, then I can my Arduino read SO when that data read is detected. I presume unless a game changes the mode, the GBA's Comm port is in Normal Mode, so I was wondering if it is even a possibility to read a specific ram address's value through the Comm port, since I know how to interpret that inputs that are stored in the IORAM, if I could actually get the information from the port on the GBP. It seems like every page I've found that looks like it has the piece I'm looking for doesn't exist anymore, sadly. Any pointers or tips are greatly appreciated. Thank you.