Commodore 64 uses Raspberry Pi to run Doom at 50fps

In short: Hobbyists will try to run Doom on anything, but the Commodore 64’s new transformation is unique. Effort uses a Raspberry-based app to run the game surprisingly well, as neither piece of hardware can work alone. The mod includes instructions so Commodore owners can set up a demo and run other Raspberry-enhanced software for themselves.

Modder “frntc” recently introduced an expansion cartridge for the Commodore 64 that allows the iconic home computer and its siblings to run programs once thought unimaginable on an 8-bit platform. What better way to test a device than to have it play Doom?

Technically, a Linux-based Commodore Doom already exists. port. Despite a needed SuperCPU upgrade, it runs with degraded colors at barely playable frame rates due to a complete lack of optimization for older hardware.

A comparison of the version on frntc’s RAD expansion unit shows the difference between night and day. The hobbyist’s system uses a copy of Doom, which is similar to the low detail mode of the DOS version running at 320×200. Created for PAL CRT, it runs at 50 frames per second – significantly faster than the original DOS-loaded game.

Based on the Raspberry Pi, the expansion cartridge does most of the work by bypassing the Commodore CPU in favor of an ARM RP processor. The C64 converts the framebuffer to display the image, handles keyboard and mouse input, and transmits an impressive 22050Hz audio sample through its SID chip.

Expansion chips that improve the basic capabilities of a platform were quite common for computers and video game consoles in the 80s and 90s. The Super NES version of Doom uses the SuperFX chip, which was best known for allowing the console to display 3D polygons in the original Star Fox.

Curious users can buy or build RAD cartridges through frntc instructions. The Commodore 64 and 128 compatible device comes in two interchangeable variants, one based on the dimensions of the Raspberry Pi 3A+/3B+ and the other modeled after the Raspberry Pi Zero 2. Some components require a 3D printer to assemble. Retro-store.de (German) offers prefabricated blocks for approx. 20€.

The RAD version of Doom is also available on GitHub frntc with a simple instructions to start playing. This requires the shareware version of Doom on doom1.wad.