A USB physical device’s logical composition is shown in Figure 5-4 and includes the following:
• USB bus interface
• USB logical device
• Function
USB physical devices provide additional functionality to the host. The types of functionality provided by
USB devices vary widely. However, all USB logical devices present the same basic interface to the host.
This allows the host to manage the USB-relevant aspects of different USB devices in the same manner.
To assist the host in identifying and configuring USB devices, each device carries and reports configurationrelated
information. Some of the information reported is common among all logical devices. Other
information is specific to the functionality provided by the device. The detailed format of this information
varies, depending on the device class of the device.
For a complete discussion of USB devices, refer to Chapter 9.