Mario Artist Paint Studio printing on a Game Boy Printer

Mario Artist Paint Studio (released on the Nintendo 64DD) has a Game Boy Printer feature that can't be used with standand accessories. It needs the "64GB Cable", an accessory Nintendo never released. It was a cable connecting a Gameboy cartridge to the N64 throught the controller port. Without it, the printer icon simply never appears in the menu. So I spent a bit of time working out what that cable actually was, and then built one. The inspiration comes from the work already done by Luigiblood some years ago (https://luigiblood.tumblr.com/post/1873484.... After digging a bit in the disk: it's a JoyBus device in a plain controller port, which identifies itself with the wire bytes 00 03. The game talks to it with pak-style 32-byte read/write commands (0x13/0x14) into a tiny register file: wake, header, TX, RX. That's the whole thing. The cable is a transparent byte pipe. Paint Studio builds real Game Boy Printer packets itself and reads back the printer's keepalive and status bytes. Which means no disk patch and no ROM hack are needed. You just need something that answers like the cable on one end and behaves like a Game Boy on the other. My bridge is a Raspberry Pi Pico (JoyBus in PIO, the cable's register file, and GB link master toward the printer) plus an Arduino Uno doing nothing but 5 V level shifting, because that's what was on my desk. And it worked. The printer icon shows up, hit print, and a drawing you made in 2D Paint comes out on real thermal paper.