Chapter 20: Hub Configuration

Reading the Hub’s Descriptors

Hubs have a class specific descriptor called the hub descriptor. This descriptor contains information about the hub implementation. The hub class descriptor is read via the class specific “Get Descriptor” request.

Figure 20-1: Required Hub Endpoints

Hubs, like other devices, also contain standard descriptors that must be read to determine how to configure the hub. Standard descriptors are read via the standard request, Get Descriptor. Hubs contains the following standard descriptors, as illustrated in Figure 20-2:

•Each USB device contains a single device descriptor that describes the number of configurations supported by the device.

•Each device contains one or more configuration descriptors that describe one or more interfaces.

•Each interface descriptor defines the number of endpoints related to the interface.

•Endpoint descriptors specify the attributes associated with a given endpoint along with information needed by host software to determine how the endpoint should be accessed.

•String descriptors are optional and consist of a UNICODE string that provides human-readable information that can be displayed.

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