OpenHCI - Data Transfer Types

There are four data transfer types defined in USB（USB中有4种数据传输类型）. Each type is optimized to match the service requirements between the client software and the USB device. The four types are:

• Interrupt Transfers（中断传输） - Small data transfers used to communicate information from the USB device to the client software.（一般应用在少量数据的通信） The Host Controller Driver polls（轮询） the USB device by issuing tokens（令牌） to the device at a periodic interval（周期性间隔） sufficient for the requirements of the device.（USB主控制器驱动通过令牌周期性地轮询USB设备）
• Isochronous Transfers（同步传输） - Periodic data transfers with a constant data rate（数据速率不变的周期性数据传输？）. Data transfers are correlated in time between the sender and receiver.
• Control Transfers（控制传输） - Nonperiodic data transfers used to communicate configuration/command/status type information between client software and the USB device.（用于USB主控制器和USB设备之间“配置、命令、状态等类型”的信息交换？）
• Bulk Transfers（批量传输） - Nonperiodic data transfers used to communicate large amounts of information between client software and the USB device.（大量数据的传输）

In OpenHCI the data transfer types are classified into two categories: periodic and nonperiodic（OpenHCI中，数据传输的类型分为周期性和非周期性两类）.

• Periodic transfers are interrupt and isochronous（周期性传输为中断传输和同步传输） since they are scheduled to run at periodic intervals.
• Nonperiodic transfers are control and bulk（非周期性传输为控制传输和批量传输） since they are not scheduled to run at any specific time, but rather on a time-available basis.

《OpenHCI - Open Host Controller Interface Specification for USB》