Core Assignment

Core Assignment decides how a content item or folder starts. It stores the selected system, core, player, catalogue, lookup setting, CPU governor and control profile together so the launch path is repeatable.

Assigning content

From Explore Content, highlight a game or folder, press X to open Content Options, then open Core.

  1. Choose a namespace such as Handheld, Home Console, Arcade or Computer.
  2. Choose the system.
  3. Choose a core. Press Left or Right where the same core is available through more than one player.
  4. Choose the assignment scope.
Scope Result
Content Applies only to the selected file.
Directory Applies to content directly inside the current folder.
Recursive Applies to the current folder and its subfolders.

Content-specific settings take priority over a directory assignment. A nearer directory assignment takes priority over a recursive assignment inherited from a parent folder.

Additional Cores

Core Assignment shows the systems and cores that suit most people, which keeps each list short. Many more come with MustardOS but stay out of sight until you ask for them, so a system or core you expected may seem to be missing.

Open AdvancedIn Configuration, highlight General, press X and confirm the warning.
Switch it onIn the System section, set Additional Cores to Enabled, then leave the screen and save the change.
Assign as usualThe extra systems and cores now appear in Core Assignment beside the main ones.

With Additional Cores enabled:

  • extra systems appear in the system list, such as the Atari Jaguar, GCE Vectrex, Mattel Intellivision, the 3DO, the Sinclair ZX Spectrum and several Commodore computers, along with game engines such as OpenLara and PuzzleScript;
  • extra cores appear for the main systems, such as further MAME and FinalBurn Alpha versions for Arcade, more Game Boy, NES and SNES cores, and melonDS for the Nintendo DS;
  • Core Management lists the extra Libretro cores, so they can be installed and updated.

Turning the setting off again only shortens the lists. Content already assigned to an extra system or core keeps working, and folders with a recognised name are still assigned to an extra system automatically. The Systems pages list every core for each system, with the extra ones marked Additional.

A few cores only appear on the devices that can run them. The Nintendo 3DS, for example, is only listed on the RG Vita Pro, because Azahar is its only emulator.

Automatic assignment

MustardOS builds an assignment index from the friendly names in core.json. Folder names are converted to lower case and stripped of spaces, hyphens, underscores and plus signs before lookup. A matching system uses its default core.

Defaults are resolved in this order:

  1. Pickles
  2. RetroArch
  3. External

This order only applies when a new automatic assignment is created. A manual choice stays assigned until you change or remove it.

Core Management

Open Configuration > Core Management to see published Libretro cores.

  • Update means a newer published build is ready. Updates appear alphabetically at the top.
  • Not Installed means the core is available to download.
  • Installed means the installed build matches the published build. It can be reinstalled.

Cores that are only used by Additional Cores are left out of this list until that setting is enabled.

A network connection is required to refresh, install, update or reinstall a core. External emulators are supplied and maintained separately from the Libretro core catalogue.

Where assignments are stored

Assignments are kept on the system partition under /opt/muos/share/info/content, in a folder for each content directory. Directory assignments use core.cfg, recursive assignments use core_recursive.cfg, and content overrides use a matching .cfg filename. Related governor and control overrides are stored beside them.

The generated files are an internal format. Use the Core Assignment screen for normal changes. Developers adding a new system or launch choice should use the Core Assign Reference.