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Linux USB驅(qū)動(dòng)程序基礎(chǔ)

來(lái)源: ChinaUnix博客日期：2008.04.10 23:55(共有條評(píng)論) 我要評(píng)論

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Linux USB Driver Basics

Introduction

Drivers are software components that operating systems use to provide

hardware specific services to applications. This webpage attempts to document

the basics of USB drivers on Linux. The goal here is to provide you with a basic understanding of how USB device drivers on Linux work.

The File Abstraction

Linux, like other Unix derived operating systems, tries to make applications simpler by providing a common hardware abstraction, the File. Essentially, interactions with almost all hardware can be abstracted into the same interface

that the operating system provides for manipulating files. Hence, you can "Open"

a driver, "Read" a driver, "Write" to a driver and "Close" a driver. This

abstraction extends all the way into the application, who can use the same

system calls that it uses to open and manipulate files to talk to hardware.

The way this works is that the kernel creates nodes in the file system,

typically located in /dev that represent a particular interface to a driver. To

talk to a particular driver an application will open the /dev entry associated

with that driver. The file descriptor returned by that open is passed to all

future system calls (read, write, select), and is eventually passed to

close.

Besides drivers, Unix also uses this file paradigm for various different

kinds of IPC, and even for socket communications over a network.

It is quite surprising how many completely different kinds of hardware can be modeled with just 4 operations (open, close, read and write). That said, their

is another very important system call that unix applications developers commonly use, select(). The select() system call allows applications to poll and

determine whether data could be read from, or written to a file descriptor

without blocking.

Sometimes a piece of hardware provides some functionality that doesn't fit

well into this file centric paradigm. To allow for this, unix applications

typically make use of the ioctl() system call. This call takes a numeric value

that is essentially an identifier for a specific piece of functionality in the

driver.

The Job of the Device Driver

Simply stated, it is the job of the driver to provide functions that the

kernel can use to implement this file programming paradigm. Applications do not directly call functions in the driver, instead they call functions in libc that

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