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Terms and Definitions

The following terms will be used throughout this manual:

USB

Universal Serial Bus.

USBD

Universal Serial Bus Driver; also called the USB protocol stack. The host controller independent part of RTUSB-32 is a USBD.

HCD

USB Host Controller Driver. RTUSB-32 contains four HCDs: UHCI, OHCI, EHCI, and XHCI.

UHCI

Universal Host Controller Interface. A host controller specification by Intel for USB 1.1 compatible controllers for Low- and Full-Speed devices.

OHCI

Open Host Controller Interface. A host controller specification by Compaq, Microsoft, and National Semiconductor for USB 1.1 compatible controllers for Low- and Full-Speed devices.

EHCI

Enhanced Host Controller Interface. A host controller specification by Intel for USB 2.0 compatible controllers for Low-, Full-, and High-Speed devices.

XHCI

eXtensible Host Controller Interface. A host controller specification by Intel for USB 3.0/3.2 compatible controllers for Low-, Full-, High-, SuperSpeed, and SuperSpeedPlus devices.

USB Client

Driver software which can handle a USB device interface using RTUSB-32's low-level API. A client can be a class driver or a part of a user application.

Hub

A USB device that provides additional connections to the USB.

Host

The computer controlling the USB and running RTUSB-32.

Frame

Basic time unit (1 millisecond) used by Low/Full-Speed USB devices. Isochronous endpoints can transfer one packet per frame.

Microframe

Basic time unit (125 microseconds) used by High-Speed, SuperSpeed, and SuperSpeedPlus USB devices.

Low-Speed

USB device operating at a transfer speed of 1.5 megabits per seconds.

Full-Speed

USB device operating at a transfer speed of 12 megabits per seconds.

High-Speed

USB device operating at a transfer speed of 480 megabits per seconds.

SuperSpeed

USB device operating at a transfer speed of 5 gigabytes per seconds.

SuperSpeedPlus

USB device operating at a transfer speed of 10 gigabytes per seconds.

Control Transfer

Transfer type for configuration/command/status type communications with a device.

Bulk Transfers

Transfer type for non-periodic, large bursty communication typically used for a transfer that can use any available bandwidth and can also be delayed until bandwidth is available.

Interrupt Transfers

Transfer type for small data, non-periodic, low-frequency, and bounded-latency.

Isochronous Transfers

Transfer type for periodic, continuous communication between host and device.

Class

A USB Class is a group of USB devices with common characteristics. A USB class specification defines a minimal set of properties and interfaces devices of that class must support. Examples for USB classes are Mass Storage Devices, Human Interface Devices, or the USB Printer class.

Transaction

A complete data transfer to or from the USB host from or to a USB device, including all required handshake and packaging.

Descriptor

Retrievable binary data structure stored in a USB device describing properties of the device.

Endpoint

A uniquely addressable portion of a USB device that is the source or sink of data in a communication flow between the host and device.

Interface

A related set of endpoints.

Configuration

A related set of interfaces. At device initialization time, the host can choose and must activate one configuration. Only one configuration can be active.

Pipe

A communication channel between an endpoint on a device and a software client on the host.

Default Control Endpoint

Endpoint 0 is available on all USB devices for all configurations and interfaces and has no endpoint descriptor. The endpoint is used to pass control and status information between the host and a USB device.

Downstream

The direction from the host to a device.

Upstream

The direction from a device to the host.

Introduction