HID Usage Tables Document 1.1 - C. Scott Ananian

Universal Serial Bus HID Usage Tables 107Appendix B: Delimiter ExampleDelimiters allow a device to declare multiple uses for a control.Ideally, an application like a flight simulator would look for the controls that are specific to it. It would firstsearch for Flight Simulation Devices attached to the system and then, if one was found, it would look forcontrols (usages) such as Flight Control Stick, Trigger, Rudder, Throttle, Landing Gear, Toe Brake, etc.The problem with a Flight Stick declaring these usages is that the same device can also be used as a genericjoystick. A device declaring itself as a Flight Simulation Device would not be found by an application thatsearched for a Joystick usage.A problem that occurs with generic buttons on an application-specific device such as a Flight Stick is thatdifferent applications use the same buttons for different purposes, forcing the user to relearn the buttons foreach application.Delimiters solve this problem by allowing multiple usages to be associated with a device or an individualcontrol. Using delimiters, a hardware vendor can suggest usages for the buttons that will allow a consistentuser interface across applications.NoteDelimiters are not allowed on top-level collections or arrays.The following example is a single device that can also be identified as a Flight Simulation Device, a FlightStick or a generic Joystick. Most of the controls also have alternate mappings:• The axes of the stick are either a Flight Control Stick or a Pointer.• The hat switch can also be used as a Point of View control.• Each of the four buttons have alternate mappings:−−−−Button 1 or TriggerButton 2 or Weapons SelectButton 3, Electronic Counter Measures, or Flare ReleaseButton 4, Landing Gear, or Chaff ReleaseButtons 3 and 4 thus have two alternate usages.Note that the report generated by this Report descriptor is identical to that generated by the joystickexample in Appendix A.UsagePage(Generic Desktop),LogicalMin(0),Usage (Joystick),Collection(Application)UsagePage(Simulation Controls),Usage (Throttle),Logical Minimum (-127),Logical Maximum (127),Report Size (8),Report Count (1),Input (Data, Variable, Absolute),Delimiter(Open),Usage (Flight Control Stick),Usage (Generic Desktop: Pointer),Delimiter(Close),Version 1.1 April 8, 1999