USB human interface device class
Encyclopedia
In computing
, the USB human interface device class (USB HID class) is a part of the USB specification for computer peripherals: it specifies a device class (a type of computer hardware
) for human interface device
s such as keyboards
, mice
, game controller
s and alphanumeric display device
s.
The USB HID class is defined in a number of documents provided by the USB Implementers Forum
's Device Working Group. The primary document used to describe the USB HID class is the Device Class Definition for HID 1.11.
The same HID protocol is used unmodified in Bluetooth
human interface devices. The Bluetooth profile specification only points readers to the USB HID documentation. In this sense those devices also belong to the USB HID class.
Keyboards: Keyboards are some of the most popular USB HID class devices. The USB HID class keyboard is normally designed with an IN endpoint that communicates keystrokes to the computer and an OUT endpoint that communicates the status of the keyboard's LEDs from the computer to the keyboard. The PC 97 standard requires that a computer's BIOS
must detect and work with USB HID class keyboards that are designed to be used during the boot process.
Mice: Computer mice are equally popular USB HID class devices. USB HID mice can range from single-button simple devices to multi-button compound devices. Most modern operating systems ship with drivers for standard HID mice designs (the most common modern mouse design has two dedicated buttons and a mouse wheel that doubles as the third button); mice with extended functionality require custom drivers from the manufacturer.
Game controllers: Modern game controllers and joystick
s are often USB HID class devices. Unlike legacy game port
devices, USB HID class game devices do not normally require proprietary drivers to function. Nearly all game devices will function using onboard drivers as long as the device is designed around the drivers and the USB HID class specifications.
Other devices: The USB HID class specifications allow for myriad other devices under the USB HID class. Some examples are automobile simulation controllers, exercise machines, telephony
devices, thermometers, audio controls and medical instrumentation. Even uninterruptible power supplies declare themselves under this class, despite the fact they often have no human interface at all. Any device can be a USB HID class device as long as a designer meets the USB HID class logical specifications. This is not to say that there is no need to ship drivers for these devices, nor that an operating system will immediately recognize the device. This only means that the device can declare itself under the human interface device class.
s available in most modern operating systems. The USB HID class devices and their basic functions are defined in USB-IF documentation without any specific software in mind. Because of these generic descriptions, it is easy for operating system designers to include functioning drivers for devices such as keyboards, mice, and other generic human interface devices. The inclusion of these generic drivers allows for faster deployment of devices and easier installation by end-users.
The interface devices are also defined with subclass descriptor
s. The subclass descriptor is used to declare a device bootable. A boot device meets a minimum adherence to a basic protocol and will be recognized by a computer's BIOS
.
Each USB HID interface communicates with the host using either a control pipe or an interrupt pipe. Isochronous and bulk pipes are not used in HID class devices. Both IN and OUT control transfers are required for enumeration; only an IN interrupt transfer is required for HID reports. OUT interrupt transfers are optional in HID-class devices.
The host periodically polls the device's interrupt IN endpoint during operation. When the device has data to send it forms a report and sends it as a reply to the poll token. Common devices such as keyboards and mice send reports that are well-defined by manufacturers such as Microsoft
. When a vendor makes a custom USB HID class device, the reports formed by the device need to match the report description given during enumeration and the driver installed on the host system. In this way it is possible for the USB HID class to be extremely flexible.
is complicated and can be difficult to understand. Despite the complexity, developers who wish to do basic things with the API need only learn a small portion of it. The primary challenge in learning the API lies in determining which parts one needs to use.
There are two levels of APIs related to USB HID: the USB level and the operating system
level. At the USB level, there is a protocol for devices to announce their capabilities and the operating system to parse the data it gets. The operating system then offers a higher-level view to applications, which do not need to include support for individual devices but for classes of devices. This abstraction layer
allows a game to work with any USB controller, for example, even ones created after the game.
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, the USB human interface device class (USB HID class) is a part of the USB specification for computer peripherals: it specifies a device class (a type of computer hardware
Computer hardware
Personal computer hardware are component devices which are typically installed into or peripheral to a computer case to create a personal computer upon which system software is installed including a firmware interface such as a BIOS and an operating system which supports application software that...
) for human interface device
Human interface device
A human interface device or HID is a type of computer device that interacts directly with, and most often takes input from, humans and may deliver output to humans. The term "HID" most commonly refers to the USB-HID specification. The term was coined by Mike Van Flandern of Microsoft when he...
s such as keyboards
Keyboard (computing)
In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...
, mice
Mouse (computing)
In computing, a mouse is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of an object held under one of the user's hands, with one or more buttons...
, game controller
Game controller
A game controller is a device used with games or entertainment systems used to control a playable character or object, or otherwise provide input in a computer game. A controller is typically connected to a game console or computer by means of a wire, cord or nowadays, by means of wireless connection...
s and alphanumeric display device
Display device
A display device is an output device for presentation of information in visual or tactile form...
s.
The USB HID class is defined in a number of documents provided by the USB Implementers Forum
USB Implementers Forum
The USB Implementers Forum is a non-profit organisation to promote and support the Universal Serial Bus. Its main activities are the promotion and marketing of USB, Wireless USB, USB On-The-Go, and the maintenance of the specifications, as well as a compliance program.It was formed in 1995 by the...
's Device Working Group. The primary document used to describe the USB HID class is the Device Class Definition for HID 1.11.
Devices
The USB HID class describes devices used with nearly every modern computer. Many predefined functions exist in the USB HID class. These functions allow hardware manufacturers to design a product to USB HID class specifications and expect it to work with any software that also meets these specifications.The same HID protocol is used unmodified in Bluetooth
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
human interface devices. The Bluetooth profile specification only points readers to the USB HID documentation. In this sense those devices also belong to the USB HID class.
Keyboards: Keyboards are some of the most popular USB HID class devices. The USB HID class keyboard is normally designed with an IN endpoint that communicates keystrokes to the computer and an OUT endpoint that communicates the status of the keyboard's LEDs from the computer to the keyboard. The PC 97 standard requires that a computer's BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
must detect and work with USB HID class keyboards that are designed to be used during the boot process.
Mice: Computer mice are equally popular USB HID class devices. USB HID mice can range from single-button simple devices to multi-button compound devices. Most modern operating systems ship with drivers for standard HID mice designs (the most common modern mouse design has two dedicated buttons and a mouse wheel that doubles as the third button); mice with extended functionality require custom drivers from the manufacturer.
Game controllers: Modern game controllers and joystick
Joystick
A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Joysticks, also known as 'control columns', are the principal control in the cockpit of many civilian and military aircraft, either as a center stick or...
s are often USB HID class devices. Unlike legacy game port
Game port
The game port is a device port found on IBM PC compatible systems throughout the 1980s and 1990s. It was the traditional connector for joystick input devices until superseded by USB in the 21st century....
devices, USB HID class game devices do not normally require proprietary drivers to function. Nearly all game devices will function using onboard drivers as long as the device is designed around the drivers and the USB HID class specifications.
Other devices: The USB HID class specifications allow for myriad other devices under the USB HID class. Some examples are automobile simulation controllers, exercise machines, telephony
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....
devices, thermometers, audio controls and medical instrumentation. Even uninterruptible power supplies declare themselves under this class, despite the fact they often have no human interface at all. Any device can be a USB HID class device as long as a designer meets the USB HID class logical specifications. This is not to say that there is no need to ship drivers for these devices, nor that an operating system will immediately recognize the device. This only means that the device can declare itself under the human interface device class.
Drivers
One of the benefits of a well-defined specification like the USB HID class is the abundance of device driverDevice driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s available in most modern operating systems. The USB HID class devices and their basic functions are defined in USB-IF documentation without any specific software in mind. Because of these generic descriptions, it is easy for operating system designers to include functioning drivers for devices such as keyboards, mice, and other generic human interface devices. The inclusion of these generic drivers allows for faster deployment of devices and easier installation by end-users.
Functional characteristics
The USB human interface device class can be used to describe both device and interface classes. The interface class is used when a USB device can contain more than one function. It is possible, therefore, to have USB devices with two different interfaces at the same time (for example, a USB telephone may use a keypad covered by the HID cass and a speaker covered by the USB audio device class).The interface devices are also defined with subclass descriptor
Descriptor
Descriptor may refer to*file descriptor, an abstract key for accessing a file*index term, also known as a "descriptor" in information retrieval*molecular descriptor, which helps characterize a chemical compound...
s. The subclass descriptor is used to declare a device bootable. A boot device meets a minimum adherence to a basic protocol and will be recognized by a computer's BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
.
Each USB HID interface communicates with the host using either a control pipe or an interrupt pipe. Isochronous and bulk pipes are not used in HID class devices. Both IN and OUT control transfers are required for enumeration; only an IN interrupt transfer is required for HID reports. OUT interrupt transfers are optional in HID-class devices.
Reports
the USB HID class requires that every device describes how it will communicate with the host device in order to accurately predict and define all current and future human interface devices. During enumeration the device describes how its reports are to be structured so that the host device can properly prepare to receive this information.The host periodically polls the device's interrupt IN endpoint during operation. When the device has data to send it forms a report and sends it as a reply to the poll token. Common devices such as keyboards and mice send reports that are well-defined by manufacturers such as Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
. When a vendor makes a custom USB HID class device, the reports formed by the device need to match the report description given during enumeration and the driver installed on the host system. In this way it is possible for the USB HID class to be extremely flexible.
USB HID API
The USB HID APIApplication programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
is complicated and can be difficult to understand. Despite the complexity, developers who wish to do basic things with the API need only learn a small portion of it. The primary challenge in learning the API lies in determining which parts one needs to use.
There are two levels of APIs related to USB HID: the USB level and the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
level. At the USB level, there is a protocol for devices to announce their capabilities and the operating system to parse the data it gets. The operating system then offers a higher-level view to applications, which do not need to include support for individual devices but for classes of devices. This abstraction layer
Abstraction layer
An abstraction layer is a way of hiding the implementation details of a particular set of functionality...
allows a game to work with any USB controller, for example, even ones created after the game.
External links
- USB.org: The homepage of the USB Implementers Forum, Inc.
- USB in a Nutshell
- Microsoft Related HID Documentation: The USB-IF's collection of Microsoft's HID documentation.
- USB-IF HID Tools: The USB-IF's page devoted to human interface devices. Includes all approved documentation.
- Lakeview Research HID Page: A collection of articles about, and example code for USB HID devices.
- PC System Guides: Microsoft's PC System specifications (e.g. PC '97, PC '98).