You determine the type of controller being used by passing an I/O request
to the device with GPD_ASKCTYPE set in io_Command, 1 set in io_Length and
the number of the unit set in io_Unit. The gameport device will respond
with the type of controller being used.

   struct IOStdReq *GameIO;  /* Must be initialized prior to using */

   BYTE GetControllerType()
   {
   BYTE controller_type = 0;

   GameIO->io_Command = GPD_ASKCTYPE;         /* get type of controller */
   GameIO->io_Data = (APTR)&controller_type;  /* place data here */
   GameIO->io_Length = 1;
   DoIO(GameIO);
   return (controller_type);
   }

The BYTE value returned corresponds to one of the five controller types
noted above.