Someone got DOOM running on the Casio Loopy, and it actually works

The Casio Loopy was built for drawing, character design and printing colourful stickers. Now it runs DOOM, with working music, adapted controls, hardware-assisted sound effects and printable screenshots. The Casio Loopy probably isn’t the first machine you think of when someone mentions DOOM. That’s understandable. Casio released the console in Japan in 1995 with a built-in colour sticker printer, a small controller and a software line aimed almost entirely at female gamers. Its games focused on drawing, fashion, character creation and light simulation. Fast first-person shooters weren’t part of the plan. Now they are. LoopyDOOM brings a working version of id Software’s shooter to the machine, and it does far more than play a video or display a technical demo. The port runs the DOOM engine on the Loopy itself, with custom code handling graphics, controls, timing, audio and even the printer. It’s not finished yet. Still, it already runs a substantial part of the shareware episode on original hardware.

The Casio Loopy was never a typical console

Casio launched the Loopy in Japan on 19 October 1995 under the full name My Seal Computer SV-100. It arrived in a market dominated by systems with far bigger software libraries and much stronger gaming identities. Sony had the PlayStation. Sega had the Saturn. Nintendo still held a huge share of the home-console market. Casio chose another path.

The company built the Loopy around creativity rather than arcade conversions, fighting games or early 3D graphics. Its advertising, visual design and software all targeted female players, especially younger users interested in illustration, fashion and character customisation. That approach shaped everything.

Players could create characters, decorate pictures and turn images into small colour stickers using the printer inside the console. Several games centred on clothing, fortune-telling, design or everyday simulation. The printer wasn’t a novelty added at the last minute. It was the main selling point.

Casio also released an accessory called the Magical Shop. It could capture images from an external video source, allowing users to add text or decorations before printing them. The Loopy supported a mouse too, although it only had one standard controller connection. It was an unusual machine. Even then.

Limited hardware, but not useless hardware

Inside the Loopy sits a Hitachi SH7021, a 32-bit SuperH RISC processor running at 16 MHz. The console includes 1 MB of RAM and 2 MB of ROM. Those numbers look tiny now. They were still enough for the kind of software Casio expected the system to run. The Loopy could display graphics using a 512-colour palette, which suited bright character art, drawing tools and menu-heavy games.

Its audio system supported four channels of 12-bit PCM sound. That gave developers access to sampled audio, but it didn’t make the machine an easy fit for DOOM. The console used cartridges, composite video output and custom Casio hardware that wasn’t designed with PC-style game engines in mind. The software library stayed very small.

Only 11 titles appeared when the Magical Shop software is included. New game development ended in November 1996, although Casio continued producing the machine until December 1998. That short life explains why many players have never heard of it. It also explains why getting DOOM running takes much more than a quick recompile.

This is a real port

LoopyDOOM comes from a code family that starts with the original DOOM source release and continues through later projects such as PrBoom and GBADoom. That helps, but only up to a point. The Loopy doesn’t behave like a DOS PC, a Game Boy Advance or a modern computer. It needs its own systems for drawing frames, reading buttons, keeping time, playing music and talking to the printer. The port adds those systems.

The current build includes maps E1M1 through E1M6 from the shareware episode. They fit inside a 4 MB cartridge image, which places a clear limit on how much game data the machine can hold at once. Graphics run through the Loopy’s 8-bit bitmap layer. Double buffering reduces screen tearing by letting the console prepare a new frame before displaying it.

Performance sits at roughly 8 to 15 frames per second on original hardware. That’s slow by modern standards. There’s no point pretending otherwise.

Yet the game still works. You can move through levels, shoot enemies, open doors, collect weapons and use the automap. The status display is there, projectiles behave as expected and the basic rhythm of DOOM survives. It isn’t just running in theory. You can play it.

The controls needed careful compromises

The Loopy controller wasn’t built for first-person shooters. It works well enough for menus, drawing tools and slower games. DOOM asks for movement, turning, strafing, firing, running, weapon changes and door controls, often within the same few seconds. There aren’t enough buttons for a direct PC-style layout.

LoopyDOOM solves this by focusing on the actions players need most. The directional pad handles movement and turning. The B button fires. The A button opens doors and activates switches, while holding it also lets the player run. The shoulder buttons handle strafing. Button combinations switch weapons, Start opens the menu and another face button activates the automap.

It takes a little adjustment. Then it starts to make sense. The layout doesn’t try to pretend the Loopy pad is a keyboard. It works with the hardware as it exists, which is the smarter choice. A port can be technically impressive and still feel terrible to play. This one avoids that trap.

The soundtrack has a different character

DOOM stores its music in the MUS format, which many ports convert into MIDI-style data. LoopyDOOM turns that music into note tables and sends it to the console’s NEC uPD937 synthesiser through a serial connection. The music runs on interrupt timing rather than through the main rendering loop. That matters.

When the frame rate drops in a busy room, the soundtrack keeps moving at the correct pace. Without separate timing, slow graphics could drag the music down too. The Loopy’s synthesiser doesn’t use the General MIDI instrument set associated with many DOOM ports. The musical parts therefore have to match the sounds available on Casio’s hardware. They’ve been assigned by ear.

The tracks remain recognisable, but they don’t sound like the PC originals. The instruments give them a lighter electronic tone that clearly belongs to another machine. Sound effects are harder. Although the Loopy supports PCM audio, its available hardware doesn’t provide a practical way to mix all of DOOM’s gunshots, monster noises and explosions alongside everything else. The port gets around this with help from the cartridge.

An RP2040 microcontroller handles the sound samples and sends the mixed audio through an added digital-to-analogue output stage. The Loopy runs the game, while the cartridge fills the gap in its audio system. Without that extra hardware, the music still works. The full sound effects don’t. It’s a practical solution, not a flashy one.

The printer finally gets its moment

The built-in printer is where the port stops feeling like DOOM on random hardware and starts feeling like DOOM on a Casio Loopy. A command in the options menu captures the current frame and sends it to the printer. That means you can print a corridor, an enemy encounter, the status screen or whatever happens to be on the display. It doesn’t change the game.

It does make the port feel complete. The Loopy originally turned customised characters and decorated pictures into physical stickers. LoopyDOOM uses the same system for monsters, weapons and grey industrial walls. The game talks to the real printer hardware. Nothing has been replaced with a simulated effect.

That’s a small detail, but it matters. Plenty of unusual ports ignore the machine’s defining features and treat it like a generic computer with a strange case. LoopyDOOM doesn’t do that. It uses the console properly.

The limits are still obvious

Running LoopyDOOM on original hardware requires compatible flash hardware and a correctly built ROM image. The game data isn’t included, so users need to provide the shareware WAD and the required interface assets. An emulator can run the port faster. It won’t reproduce every graphics limitation, and it can’t offer the physical sticker-printing function of the actual console.

The hardware also creates some firm boundaries. The SH-1 processor lacks hardware division, making certain calculations expensive. The 1 MB of RAM leaves little room for level data, graphics, engine code and working buffers. Cartridge capacity limits the number of maps. Full sound effects need extra electronics.

The frame rate changes from scene to scene too. Narrow corridors are easier on the machine than large rooms filled with enemies and projectiles. Nobody should expect smooth modern performance. That isn’t the point. LoopyDOOM shows how much the console can do when someone writes directly for its hardware. It uses the Loopy’s graphics system, controller, timing, sound hardware, cartridge interface and printer.

Six maps run. Music works. Optional sampled audio works. The controls have been adapted, and the printer can produce screenshots. For a 16 MHz console marketed towards female gamers and built around drawing tools, character design and printed stickers, that’s a serious result. The Casio Loopy still isn’t an obvious machine for DOOM. It’s now a working one.