3.5 USB Data Exchange

3.5 USB Data Exchange
	Chapter 3. WinDriver USB Overview

The USB standard supports two kinds of data exchange between a host and a device: functional data exchange and control exchange.

Functional Data Exchange is used to move data to and from the device. There are three types of USB data transfers: Bulk, Interrupt and Isochronous .
Control Exchange is used to determine device identification and configuration requirements and to configure a device, and can also be used for other device-specific purposes, including control of other pipes on the device.
Control exchange takes place via a control pipe, mainly the default Pipe 0, which always exists. The control transfer consists of a setup stage (in which a setup packet is sent from the host to the device), an optional data stage and a status stage.

Figure 3.2 below depicts a USB device with one bi-directional control pipe (endpoint) and two functional data transfer pipes (endpoints), as identified by WinDriver's DriverWizard utility (discussed in Chapter 5).

Figure 3.2 USB Pipes

More information on how to implement the control transfer by sending setup packets can be found in section 9.2.


3.4 Data Flow in USB Devices		3.6 USB Data Transfer Types