The USB Driver operates can operate in the Device mode when it is initialized for Device mode or Dual Role operation. When operating in Device mode, the USB Driver is also referred to as the USB Controller Driver (USBCD). In Dual-Role mode, the USB Driver will switch to USBCD mode when the USB Driver Device Attach function is called. 

The USB Driver Client must perform these steps to operate the USB Driver in Device mode.

1. Open the USB Driver to obtain the driver handle.
2. Set the event handler.
3. Wait for the application to attach the device to the bus.
4. Enable Endpoint 0 and respond to USB Host Enumeration requests.
5. Allow the application and function drivers to enable other endpoints and communicate with the Host.

The following sections discuss these operations in more detail.