How to Play DOOM on an 8-bit Nintendo NES

Lost titles, pirated games, movie homages, and even the content of its memory turned into art. The Nintendo NES is an enormous range of possibilities, and with 36 years on its shoulders, there's no doubt that its fans know every detail of its operation. The number of hacks for the NES is impressive, however, one was missing: playing DOOM. The YouTube channel TheRasteri teaches us to build a "cartridge" of DOOM, and although its execution is not entirely native (since it uses a Raspberry Pi), it depends completely on the original hardware, without modifications.

DOOM retains its position as the new "hello world", and some enthusiasts have managed to run it on unthinkable platforms. From thermostats to printers, these geniuses have bent and adapted the game's code in incredible ways, and one can't help but wonder what the limit is.

Perhaps... the Nintendo NES? The original shareware version of DOOM reports minimum requirements of a 386 processor with 4 megabytes of RAM. The NES processor is a tiny fraction of a traditional 386, while its RAM is only 2 kilobytes. If the marine is to traverse those infernal corridors once more on Nintendo hardware, he'll need a little help... and that's where a Raspberry Pi comes in.

DOOM on a Nintendo NES

But the story doesn't end there. This hack by TheRasteri is much more elaborate than the classic "let's install a Pi in the NES shell". In essence, what the mini computer does is run Chocolate Doom (perhaps the closest to what we enjoyed on MS-DOS, because it needs its .WAD files), and "hijack" the graphics memory bus on the NES to then inject the game graphics directly into the console's PPU. Hence the name PiPU.

The good news is that the NES receives no modification, but the Raspberry Pi and the rest of the components must be installed in a donor cartridge. The "sacrifice" was Major League Baseball, especially useful because it's a CNROM cartridge with all pins present, but it still requires surgery. The final result is DOOM in stock version on a Nintendo NES with Raspberry Pi assistance. Beyond the hack, the console only displays 13 colors in normal circumstances, so PiPU must use dithering to mask the effects.

Now the question is: is she cheating? Well... yes and no? Yes because the execution of DOOM is carried out by the Raspberry Pi, and no because the idea of using additional hardware in Nintendo cartridges is not new. The first thing that comes to mind is the Super FX coprocessor of Super Nintendo (version 2 of that chip was used in the official DOOM port for SNES), and the SA-1 coprocessor, which is still being hacked by fans.