This section is specific to the FDS functionality in Mendafen.
For details on the emulator see the main Mednafen page.
The file disksys.rom is required to run famicom disk system images. This is located on the famicom disk system cartridge.
While any game is running in Mednafen, press ALT + SHIFT + 1. This will prompt you to set and confirm all of your inputs for player 1. To set up player 2's controls, press ALT + SHIFT + 2 and repeat the process. 
Alternatively, you can edit Mednafen's config file in a text editor. Open ~/.mednafen/mednafen.cfg. Scroll down to or search for the platform "fds", and set the desired keycodes for your inputs.
;fds, Port 1, Gamepad: A fds.input.port1.gamepad.a keyboard 122
Reassigning Save State Keys
The number keys are used to select save states. If you have 1 and 2 mapped to your start buttons and you want to disable the save state messages that appear when you press them, you will need to remap the save state keys. Scroll down in the mednafen.cfg file to ";Save" and make the following changes:
;Save state 1 select command.1 keyboard 0 ;Save state 2 select command.2 keyboard 0
Now you can map player 1 start to the 1 key, and player 2 start to the 2 key, without conflicting with the save state selector.
Flipping the Disk to Side B
F6 will select disk and disk side. F8 will eject or insert disk. These keys may be reassigned by modifying the mednafen.cfg file (see above).
VS. Uni System Games
If you use Mednafen for Vs. Unisystem games, F8 Insert coin. F6 Show/Hide dip switches. 1-8 Toggle dip switches (when dip switches are shown. These keys may be reassigned by modifying the mednafen.cfg file (see above).
Exit on ESC
ESC exits the emulator by default.
The help menu is accessible at any time by pressing F1.
- mednafen.sourceforge.net - Mednafen homepage