FreeBSD Device Drivers

More About USB Devices

The endpoints on a USB device are grouped into interfaces. For example, a USB speaker might define one group of endpoints as the interface for the buttons and another group of endpoints as the interface for the audio stream.

All interfaces have one or more alternate settings. An alternate setting defines the parameters of the interface. For example, a lossy audio stream interface may have several alternate settings that provide increasing levels of audio quality at the cost of additional bandwidth. Naturally, only one alternate setting can be active at a time.

Note

The term “alternate setting” is kind of a misnomer, as the default interface setting is the first alternate setting.

Figure 15-1 depicts the relationship between ...