The General USB Process
How Does the Host Know a Device’s Requirements?
Software – General Concepts
Device Descriptor
Since the device descriptor represents the entire device, there can be only one per device. This descriptor specifies basic information such as: USB version supported, maximum packet size, the number of configurations, and vendor and product ID info.
//Sample Standard Device Descriptor Type
//Definition Fields
Length (18 bytes)
Descriptor Type (DEVICE)
USB Spec Release Number (0200h)
Device class (hub type…Human Interface defined in other descriptor, CDC described here)
Device Sub-class (00h)
Device protocol (00h)
Maximum Packet size (64 bytes – max for the 
endpoint)
Vendor ID (ID assigned by USB IF)
Product ID (ID assigned by product manufacturer) Device release number (revision code of device) Manufacturer (ABC Corp)
Product (string identifier) Serial Number (1234)
Number of configurations (1 or more configurations can follow)
