HID Related Specifications Device Class Definition HIDThe Device Class Definition for HID 1.11 is intended to supplement the USB Specification and provide HID manufacturers with the information necessary to build USB-compatible devices. It also specifies how the HID class driver should extract data from USB devices. The primary and underlying goals of the HID class definition are to: be as compact as possible to save device data space allow the software application to skip unknown information be extensible and robust support nesting and collections be self-describing to allow generic software applications HID Usage Tables The HID Usage Tables 1.12 document defines constants that can be interpreted by an application to identify the purpose and meaning of a data field in a HID report. Usages are also used to define the meaning of groups of related data items. This is accomplished by the hierarchical assignment of usage information to collections. Usages identify the purpose of a collection and the items it contains. Each Input, Output, Feature, and/or Collection data item within a Collection item can be assigned a purpose with its own usage item. Usages assigned to a collection apply to the items within the collection. The HID Usage Tables document contains extensions to the tables defined in the USB Device Class Definition for Human Interface Devices. All usages pages, except the Keyboard table, are replicated in the Usage Table document. The Usage Table document identifies the extensions to the Keyboard usage table. Note: For keyboards, look at the usage table sections in both the HID Specification and the HID Usage Table document! Approved Usage Table Review Requests The following HID Usage Table Review Requests have been approved for implementation by the USB Device Working Group HID Committee. These Review requests assign enumeration values and recommended meaning.
USB Device Classes USB is much more complex than e.g. a serial interface. The standard defines not only how the bits are transferred, but also how information about a device can be obtained by the host. Every USB device must comply to this basic protocol. When you implement a USB device, you must decide how it should present itself to the host. The basics common to all classes are handled by the driver itself. For the rest, you can choose among various device classes and each class has its advantages and disadvantages: Custom class devices The most straight forward way to implement a device is by choosing class Custom, which basically means that you comply to no known class. Data can be transferred in blocks up to 254 bytes in both directions over the default control endpoint. An example for a very simple custom class device is Power Switch. If required, interrupt endpoints can be added for stream-type data or to send spontaneous notifications to the host. An example for this can be found in the Remote Sensor project. Advantages: Easy to implement on the device. Easy to write host side software on Unix. Disadvantages: On Windows, a driver DLL must be installed. This means that the host application can't be run without installation. You must provide software for the host to control the device. We recommend libusb or libusb-win32 for implementing the host software. Standard HID class device You can design your device to look like a standard USB keyboard, mouse or joystick and every application will be interoperable with your device without additional drivers. Since you adhere to the class specification, the operating system's driver knows how to communicate with your device. Advantages: No driver required on host. Disadvantages: Can only be used for standardized Human Interface Devices like mice, keyboard, joystick, power source, point-of-sale equipment etc. A HID Report.
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