The USB protocol: endpoints and more


Each device features a vendor and device ID, plus class
Vendor and device are 16 bits wide
This is artificial scarcity, designed by a greedy consortium
USB identifiers are very expensive, and must be renewed

Devices can feature more than one "Interface"
Packets are addressed to a specific interface
Each interface is like a separate device

Each interface features several "endpoints"
Packets are addressed to a specific endpoint
USB-1 was talking about "pipes", a now-forgotten word
Endpoints were the end points of each pipe
An endpoint can be either input or output (as seen from the host)
The standard defines 3 types of endpoints are defined (and "control")