The firmware for the Holoseat can be found in the SVN Repository. Its basic function is to detect pedal events from the reed switch, use the timing of those events to determine the pedal speed (in steps per minute), and then send the walk command (generally by pressing the 'w' key) when the pedal speed is greater than the specified trigger speed.
As the Holoseat only controls locomotion, you will need to use a keyboard or a controller for other inputs. One of the Holoseat developers prefers to play games on a recumbent exercise bike, and in turn uses a controller. For PC games, he uses JoyToKey to map an XBox 360 Wired controller to keystrokes. Below are the configuration files for the games he has played using the Holoseat.
To use these files, download and unzip JoyToKey, then download the cfg file(s) for the game in question to the JoyToKey executable directory. The next time you run JoyToKey (note, the JoyToKey developer recommends running JoyToKey as an administrator), the configuration(s) you downloaded will be listed. Simply select the one matching the game you want to play and things should be ready to go. Browse the key mappings in JoyToKey to see how the controller has been configured. Note, the walk command (w) is not mapped in these config files as the Holoseat will provide this input.