RNDS-Stream Puts Minecraft and Counter-Strike 2 on an Eighteen Year Old Nintendo DSi

Across the room from a Linux PC, a Nintendo DSi is drawing Minecraft Java Edition on a pair of 256 by 192 screens that first shipped in 2008. Counter-Strike 2 shows up the same way. Video decoding happens on the handheld. A server on the computer only has to capture a window, squeeze each frame into a JPEG, and send the pile across the local network.

Gaff, aka gavff64, is the man behind RNDS-Stream. The project consists of two parts: a homebrew file that runs from a flashcart and a server packaged as a flatpak that can display an X11 or Wayland window. They are both from RubyNDS, a package Gaff put together for building DSi software in Ruby, which is partly because he like the language. MJPEG encompasses the entire video chain, which is not as strange as it may sound. Ruby was an obvious choice because RubyNDS already has JPEGDEC, a small decoder that can convert a JPEG into pixels quickly even on machines without their own video decoder. GStreamer on the PC then captures the game window, jpegs the frames, and delivers them to the client; because frames are skipped on purpose, the output is roughly 20 frames per second, which is steady enough to allow you to almost play a match at your own leisure. However, using full DSi resolution constantly reduces the frame rate to 10 or 15 frames per second, and altering the quality is as simple as adjusting the script that powers GStreamer.

Input in the other direction is a little more complicated. Your DSi button pushes and stylus gestures are converted into mouse and keyboard events on the PC, thanks to ydotool wrapped up in a Rubydotool is a Ruby development tool. The mouse must remain locked on the recorded window, and the key mapping is currently blocked in the code. Before any of that to work, the PC must be granted permission to spit out input events, which requires you to create a fast udev rule and reboot. Gaff tested it on Fedora.

Starting a game requires more than just a command line. Once the DSi client connects to the server, the server displays a list of all the Steam games and Minecraft instances that Prism Launcher is aware of. You then select one from the bottom screen, and the PC starts the stream. There’s a text file called rnds-stream.txt on the flashcart microSD that says this. It’s only the PC’s local address, and there’s a reason for it. Because the homebrew reads from the flashcart’s filesystem rather than the DSi’s own card, the internal card is completely disregarded.

Sound is nowhere to be found, and you are not even notified that your controller has been withdrawn from the session. as switching to a new game necessitates manually restarting the server. Small lettering on the present interface is difficult to see on those screens, which is to be expected given that the panel is just large enough to accommodate those old 2008 cartridges. This is only suitable for casual play, as the lack of audio keeps the opposing team silent. The DSi was the ideal retro machine for this because of one essential feature: the radio. The original DS units have a problem: their Wi-Fi security mode is an outdated one that most routers have thankfully discarded. The DSi, on the other hand, can connect to a WPA2 network and is powered by the ancient ARM946E-S processor, which operates at a decent 133 MHz and has 16 MB of RAM, which is plenty to keep up with JPEGDEC if the heavy work is offloaded to the computer. Gavff believed he required the extra speed and the newer wireless stack, and even as he built it, he was still learning the ins and outs of the hardware.

RNDS-Stream is still in its early stages, and he considers it more of a proof-of-concept for RubyNDS than a polished player. He’s shared the code on Github under an MIT license, along with some basic setup instructions for Flatpak, wmctrl, and GStreamer. Who would have believed that a clamshell Nintendo discontinued years ago might be placed on a couch to display a game that never received a cartridge? That is a strange and specific kind of second life for something that has been sitting in a drawer the entire time.
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