Commander Keen 1 just got a Sega Master System port

Developer haroldo-ok has released a free Sega Master System port of Commander Keen 1. The homebrew project is available to download today as a 144 KB ROM that runs on real hardware or emulators.

I think this is pretty cool. It got me wondering if Commander Keen ever actually released for the Sega Master System back in the day. The short answer is no. The long answer involves the very foundation of PC gaming in the early 1990s.

Carmack's smooth scrolling

Commander Keen was born on MS-DOS in 1990. At the time, IBM-compatible PCs struggled to replicate the smooth side-scrolling action found on home consoles like the Nintendo Entertainment System. John Carmack figured out a clever programming trick to force PC graphics cards to redraw the screen efficiently. He and John Romero famously used this tech to build a PC port of Super Mario Bros. 3.

Nintendo rejected their pitch. The team (which would soon become id Software) took their smooth-scrolling engine and created their own platformer instead. Billy Blaze put on his older brother's football helmet and went to Mars. The resulting shareware game was a massive hit. It proved PCs could handle fast action games. That success funded the studio and paved the way for Wolfenstein 3D and Doom.

Because of that PC-centric origin, Commander Keen stayed away from Sega and Nintendo consoles. Aside from a much later Game Boy Color release in 2001, the series was strictly a computer franchise. Sega Master System owners had Alex Kidd and Sonic the Hedgehog, but they never got to bounce on a Yorp.

Three levels on Mars

This new Master System release is technically a "vibe-port" of an HTML5 demake rather than a direct translation of the DOS original. The project is available on itch.io and was built using Claude Fable 5.

Developer haroldo-ok shared the technical structure on GitHub. The game is built with devkitSMS and SDCC. It runs the complete core loop of the original demake. You start at the title screen, move to the Mars overworld map, and play through three platforming levels.

The classic progression logic is intact. A rock gate east of the first city blocks your path on the overworld. Beating the first level opens the gate and unlocks the rest of the map. You have to collect keycards and find the exit door to clear each stage. Beating all three clears the game.

The controls map naturally to the two-button Sega pad. Button 1 jumps and enters levels. Button 2 fires the raygun. Pressing down and Button 1 activates the pogo stick. You can bounce on a Yorp's head to stun it, or shoot it with the raygun to stop it permanently. The developer also included a cheat code. Holding Button 2 and pressing Button 1 on the title screen grants the pogo stick and 99 ammo right from the start.

16x16 metatiles

Developer haroldo-ok describes the ROM as using a SEGA-mapper architecture divided into several banks. The engine code and fonts live in the first two banks. Sprite art streams to video RAM at runtime from bank two. The three playable levels each get their own dedicated bank for map data and object definitions.

The world format relies on 16x16 metatiles. These are constructed from 2x2 Sega Master System tiles. Maps and metatile definitions are read directly from the mapped ROM bank to save memory. Only the collision flags table is copied to the system RAM. Item pickups go into a small RAM override list to track what you have collected.

It is a short game, but it captures the feel of the DOS classic on hardware that never saw the original release.