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USB generic parent driver (Usbccgp.sys)

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This article describes an independent driver called the USB generic parent driver (Usbccgp.sys), provided by Microsoft for composite devices.

Many USB devices expose multiple USB interfaces. In USB terminology, these devices are called composite devices. The Windows operating system includes a generic parent facility in the USB bus driver (Usbhub.sys) that exposes each interface of the composite device as a separate device. This facility is streamlined and improved by transferring it to an independent driver called the USB generic parent driver (Usbccgp.sys). Device vendor can use the features of the generic parent driver to make selective use of Microsoft-supplied driver support for some interfaces.

The interfaces of some composite devices operate independently. For example, a composite USB keyboard with power buttons might have one interface for the keyboard and another interface for the power buttons. The USB generic parent driver enumerates each of these interfaces as a separate device. The operating system loads the Microsoft-supplied keyboard driver to manage the keyboard interface, and the Microsoft-supplied power keys driver to manage the power keys interface.

If the native Windows drivers don't support a device's interface, the vendor of the device should provide a driver for the interface and an INF file. The INF file should have an INF DDInstall section that matches the device ID of the interface. The INF file must not match the device ID for the composite device itself, because it prevents the generic parent driver from loading. For an explanation of how the operating system loads the USB generic parent driver, see Enumeration of USB Composite Devices.

Some devices group interfaces into interface collections that work together to perform a particular function. When interfaces are grouped in interface collections, the generic parent driver treats each collection, rather than each individual interface, as a device. For more information on how the generic parent driver manages interface collections, see Enumeration of Interface Collections on USB Composite Devices.

After Windows loads the client drivers for the interfaces of a composite device, the generic parent driver multiplexes the data flow from the client drivers, combining these separate interactions into a single data stream for the composite device. The generic parent is power policy owner for the entire composite device and all of its interfaces. It also manages synchronization and Plug and Play requests.

The generic parent driver can simplify the task for vendors of composite hardware, if Microsoft-supplied drivers support some interfaces but not others. Vendors of such devices need only supply drivers for the unsupported interfaces, because the generic parent driver facilitates the use of Microsoft-supplied drivers for the supported interfaces.

The following sections describe the features and functions of the generic parent driver: