Device Qualifier Descriptor in dscr.a51

Question: What is the need for Device Qualifier Descriptor in dscr.a51?

 

Answer:

The device_qualifier descriptor describes information about a high-speed capable device that would change if the device were operating at the other speed. For example, if the device is currently operating at full-speed, the device_qualifier returns information about how it would operate at high-speed and vice-versa. For more details refer section 9.6.2 of USB 2.0 Specification