HOST-SPECIFIED USB DEVICE REQUESTS

摘要

A USB device is configured to support a non-USB-defined device request that is specific to an application program or operating system. The device request is supported by using a device-specific or vendor-specific request code, which is allowed to vary from device to device. To determine the proper request code, the host performs a GE-ESCRIPTOR device request, specifying a predetermined string descriptor. The requested string descriptor designates the request code to be used in the non-USB-defined device request.