NAME
        GPD_READEVENT -- Return the next game port event.

   FUNCTION
        read game port events from the game port and put them in the
        data area of the iORequest.  If there are no pending game port
        events, this command will not be satisfied, but if there are
        some events, but not as many as can fill IO_LENGTH, the
        request will be satisfied with those currently available.

   IO REQUEST
        io_Message      mn_ReplyPort set if quick I/O is not possible
        io_Device       preset by the call to opendevice
        io_Unit         preset by the call to opendevice
        io_Command      GPD_READEVENT
        io_Flags        IOB_QUICK set if quick I/O is possible
        io_Length       the size of the io_Data area in bytes: there
                        are sizeof(inputEvent) bytes per input event.
        io_Data         a buffer area to fill with input events.  The
                        fields of the input event are:
            ie_NextEvent
                        links the events returned
            ie_Class
                        is IECLASS_RAWMOUSE
            ie_SubClass
                        is 0 for the left, 1 for the right game port
            ie_Code
                        contains any gameport button reports.  No
                        report is indicated by the value 0xff.
            ie_Qualifier
                        only the relative and button bits are set
            ie_X, ie_Y
                        the x and y values for this report, in either
                        relative or absolute device dependent units.
            ie_TimeStamp
                        the delta time since the last report, given
                        not as a standard timestamp, but as the frame
                        count in the TV_SECS field.

   RESULTS
        This function sets the error field in the iORequest, and fills
        the iORequest with the next game port events (but not partial
        events).

   SEE ALSO
        gameport.device/gpd_setctype, gameport.device/gpd_settrigger