📄 c15.html
字号:
<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN"><HTML><HEAD><TITLE>USB Introduction</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet"><LINKREL="HOME"TITLE="The Linux USB sub-system"HREF="book1.html"><LINKREL="UP"TITLE="Using the Linux USB sub-system"HREF="p13.html"><LINKREL="PREVIOUS"TITLE="Using the Linux USB sub-system"HREF="p13.html"><LINKREL="NEXT"TITLE="Host Controllers"HREF="x29.html"></HEAD><BODY><DIVCLASS="NAVHEADER"><TABLEWIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">The Linux USB sub-system</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="p13.html">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom"></TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="x29.html">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="CHAPTER"><H1><ANAME="AEN15">Chapter 1. USB Introduction</A></H1><DIVCLASS="TOC"><DL><DT><B>Table of Contents</B></DT><DT><AHREF="c15.html#AEN18">The Universal Serial Bus</A></DT><DT><AHREF="x29.html">Host Controllers</A></DT><DT><AHREF="x33.html">USB Devices and Transfer Characteristics</A></DT><DT><AHREF="x75.html">Enumeration and Device Descriptors</A></DT><DT><AHREF="x119.html">USB Device Drivers</A></DT></DL></DIV><P>This chapter provides a brief introduction into the Universal Serial Bus(USB) in general, and may be skipped if you are already familiar with thebus, and its software and hardware architecture.</P><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="AEN18">The Universal Serial Bus</A></H1><P>In 1994 an alliance of four industrial partners (Compaq, Intel, Microsoftand NEC) started to specify the Universal Serial Bus (USB). The bus wasoriginally designed with these intentions:<P></P><UL><LI><P>Connection of the PC to the telephone</P></LI><LI><P>Ease-of-use</P></LI><LI><P>Port expansion</P></LI></UL></P><P>The specification (version 1.0) was first released inJanuary 1996 and the latest official version 1.1 was released in September 1998The document is still under development and a version 2.0 wasannounced in 1999. The USB is strictly hierarchical and it is controlled by onehost. The host uses a master / slave protocol to communicate with attached USBdevices. This means that every kind of communication is initiated by the hostand devices cannot establish any direct connection to other devices. This seemsto be a drawback in comparison to other bus architectures but it is notbecause the USB was designed as a compromise of costs and performance.The master / slave protocol solves implicitly problems like collisionavoidance or distributed bus arbitration. The current implementation of theUSB allows 127 devices to be connected at the same time and the totalcommunication bandwidth is limited to 12Mbit/s. Howewer use of low speeddevices, management of USB "interrupts" and other overheads mean that actualthroughput cannot exceed about 8.5Mbit/s under near ideal conditions, andtypical performance may be around 2Mbit/s.</P></DIV></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLEWIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="p13.html">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="book1.html">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="x29.html">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">Using the Linux USB sub-system</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="p13.html">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Host Controllers</TD></TR></TABLE></DIV></BODY></HTML>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -