USB数据流模型

摘要

USB数据流模型描述了主机与外部设备之间的连接交互关系，提出了解决USB不同服务的技术实现，揭示了USB基本组织机构，反映了USB的核心内容。其表现为3个层次：应用层、逻辑设备层、总线接口层。主机通过逻辑意义上的数据流来统一对USB设备的操作方式。USB设有2种通道：流通道和信息通道；提供了4种传送方式：控制传送、同步传送、中断传送、批传送；定义了2种数据格式：USB数据格式、非USB数据格式。针对USB设备的连接，及USB所传输的数据特性，如突发性、连续性、实时性、可靠性等，USB系统软件安排了相应的通道、传送方式及数据格式。就这4种传送方式重点介绍了数据格式、传送的方向、包长限制、总线访问、传送次序等内容。%USB Data Stream Model describes the connection between hostcomputer and peripheral equipment,brings up the technological implementation that transacts different USB services,exposes the USB structure of basic organization,and mirrors the nuclear USB content well.The USB Data Stream is divided into three layers,they are Function Layer,Logical Device Layer and Bus Interface Layer.The host unifies the USB device operations by logistic data stream.USB has two types of pipe:stream pipe and message pipe.USB defines four transfer types:Synchronous Transfer,Control Transfer,Interrupt Transfer and Bulk Transfer.The USB data format and its contrary are also defined.According to the connection between host & peripheral,and the service data characteristics,such as burst,continuity,real-time and dependability,the USB system software arranges the corresponding pipe,transfer type and data format.A main introduction to the four USB transfer types is made,mainly including data format imposed by USB，communication direction，packet size constraints，bus accessing constraints，required data sequence,etc.