The native program includes a simple, curses-based user interface to show what it is doing. Switches, lamps, solenoids, and GI states are redrawn in the window as necessary. Also, the DMD or alphanumeric display is emulated.
The UI support is separated into a separate module from the core emulation, and could be replaced by something more sophiscated in the future, for example, using a window library like Qt or GTK.
Switches can be simulated by pressing keys. The ESC key terminates the simulation. Many of the key mappings are the same as what is offered in PinMAME.
Advanced simulation techniques, such as ball movements, are only partially implemented at the moment.