USB-driver lifecycle reference

Topology before function

USB software first represents a host controller, hubs, addresses, and devices in a bus topology. A physical product can then expose one or more interfaces, each with its own class or function relationship. The topology and the device function are adjacent layers, not synonyms.

Descriptors carry identity

USB descriptors describe a device, configuration, interface, endpoint, and sometimes other capabilities. Their fields help the host understand what the device presents before a function-specific driver interprets data. A descriptor is metadata about an interface, not a complete user-facing product description.

Endpoints carry transfers

Endpoints define sources or destinations and the transfer conventions used by an interface. Control, bulk, interrupt, and isochronous transfers have different purposes and timing characteristics. A driver’s lifecycle includes establishing these relationships before it exposes a higher-level function.

Package and runtime records

A USB package can declare matching identifiers, class relationships, files, services, and signatures. Runtime enumeration, selection, activation, and removal have their own states. Keeping package declarations separate from live bus traffic makes USB documentation easier to read.

Questions and answers