Category: spotlight

By Rumbleminze on April 15, 2024. Reproduced with permission.

Rumbleminze, a fan of all things retro tech, is co-author of the Kid Icarus Randomizer romhack and whose recent work includes porting NES games to run natively on the SNES. You can follow these and other projects via Rumbleminze’s IA, Github, YouTube, or Ko-Fi.

Intro

This [post] is going to go over the process I use to port NES games to the Super Nintendo. Something to keep in mind while we go through this process: I’m by no means an expert on all these things. But I do know what’s worked for me. If you have ideas on ways to improve it, I’d love to hear them! Please reach out to me on Bsky.

Why though?

The most frequent question I get is “why?”. There are a lot of great reasons for porting games from the NES to the SNES. Here’s a few:

1. eliminate slowdown
2. eliminate sprite flicker
3. allow for MSU-1 enhancements like CD quality music and videos
4. Take advantage of FastROM cartridge chips
5. Up-rez-ing the sprites to 16-bit
6. better video output on SNES instead of NES
7. Much, much more room for romhacks/enhancements
8. Most importantly, it’s fun!! Finding ways to port these games is, to me, like solving a big puzzle.

The Overall Process

To accomplish my ports, I follow this general approach:

1. Take the original NES ROM, and break it up into it’s requisite memory banks by creating .asm files for each bank.
2. Use a buildable SNES game skeleton, with the NES games memory banks mapped to various convienent banks in the SNES game.
3. Hook up the SNES skeleton to jump to the NES initialization/nmi at the proper times
4. Slowly replace routines of the NES byte code with decompiled assembly, aquired from running the NES game in Mesen2.
5. Find and modify the NES specific logic and tile graphics to work on the nes. Especially things like:
   • All writes to Video Memory
   • Deal with differences in screen resolution / BG size / Mirroring
   • Update audio to use Membler’s 2A03 emulator
   • Properly handle bank switching

[Editor’s note: for the remainder of this post, covering tools, goals, and limitations, please visit Rumbleminze’s blog.]

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