What is a game folder?


Why game folders?

A game is more than just the raw data originally encased in a game’s ROM chip. If a game allows you to save your progress, that information needs to be stored somewhere. If you use an emulator’s save states, those save states need to be stored somewhere. If you use Game Genie or Pro Action Replay codes, information about what codes exist, what codes are enabled, and what they do needs to be stored somewhere.

On the technical side, a physical game cartridge contains a circuit board that makes the game data available to the console, and different games used circuit boards that work differently. That circuit-layout information needs to be stored somewhere. Some games included custom processors to do calculations the base console could not do quickly enough (like the SuperFX chip used in StarFox for the Super Famicom) and information about extra chips needs to be stored somewhere. Some of those custom processors require extra data to work that’s not part of the main game data (like the DSP chip used in Super Mario Kart for the Super Famicom) and that data needs to be stored somewhere too.

higan keeps all this game-related information together in a single place: a game folder in the higan library.

For a more detailed motivation for game folders, see Game Paks on the higan website

What is a manifest?


The most important file in a game folder is manifest.bml, which describes how all the other files should be wired together to create a runnable game cartridge. However, the manifest format has occasionally changed as new emulation details were uncovered that could not be represented in the old format. Therefore, icarus defaults to not writing out manifests when it imports games, and higan defaults to ignoring manifests that are present. Instead, when higan loads a game, it will ask icarus to generate a temporary manifest in the latest format, based on the files present in the game folder and how they are likely to go together. You can view this temporary manifest in the Manifest Viewer.

What’s in a game folder?

As mentioned above, a game folder collects all the information relevant to emulating a particular game. Not all of the following files are relevant to every emulated console, or to every game on a given console, but they may be relevantunder particular circumstances.

All the files directly in the game folder are expected to be useful to all emulators that support them:

  • manifest.bml: The manifest for this game folder.
  • program.rom: For most consoles, this contains the executable instructions and graphics data from the cartridge’s ROM chips. For the Famicom, this contains only the executable instructions.
  • character.rom: For the Famicom, this contains only the graphics data from the cartridge’s ROM chips.
  • ines.rom: While other consoles typically include enough hints in program.rom for icarus to generate a manifest, the Famicom does not. Famicom games not stored in game folders typically include an “iNES header” to store that information, which icarus preserves after import as ines.rom.
  • save.ram: Games that include a save feature will create this file. Note that it is only written to disk when higan exits gracefully, if higan crashes or is forced to quit, in-game saves may be lost. Other emulators sometimes call this an “SRAM file”, even though the same filename is used for cartridges that use EEPROM or Flash storage, not just battery-backed Static RAM.
  • rtc.ram: Games that include a calendar or real-time clock will create this file.
  • *.data.rom, *.program.rom: Files named like this are usually co-processor firmware.
  • msu1.rom: Holds streamable data for the MSU-1.
  • track-*.pcm: Holds streamable audio for the MSU-1.

Files that are only useful to higan specifically are placed in a higan subdirectory: