22.2.3 WaitForKey and WaitForKeyEx Notification Implementation

When the WaitForKey and WaitForKeyEx events are created, they must be associated with an event notification function. This event notification function checks to see if one or more keystrokes are currently available from the console input device. If one or more keystrokes are currently available from the console input device, then the WaitForKey and WaitForKeyEx events must be placed into the signaled state by calling the UEFI Boot Service SignalEvent().