📄 introduction to device drivers.mht
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Subject: Introduction to Device Drivers
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<H1>1 Introduction to Device Drivers</H1>
<P>This chapter presents an overview of device drivers by discussing:=20
<UL>
<P>
<LI>The purpose of a device driver=20
<P></P>
<LI>The types of device drivers=20
<P></P>
<LI>Single binary module=20
<P></P>
<LI>When a device driver is called=20
<P></P>
<LI>Device driver configuration=20
<P></P>
<LI>The place of a device driver in the Digital UNIX operating system =
</LI></UL>
<P>The chapter concludes with an example of how a device driver in =
Digital UNIX=20
reads a single character. <A name=3Dpurpof_devdrv></A>
<P>
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<P>
<H2>1.1 Purpose of a Device Driver </H2>
<P>The purpose of a device driver is to handle requests made by the =
kernel with=20
regard to a particular type of device. <A name=3Dnx_id_0></A>There is a=20
well-defined and consistent interface for the kernel to make these =
requests. By=20
isolating device-specific code in device drivers and by having a =
consistent=20
interface to the kernel, adding a new device is easier. <A=20
name=3Dtypesof_devdrv></A>
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<P>
<H2>1.2 Types of Device Drivers </H2>
<P><A name=3Dnx_id_1></A>A device driver is a software module that =
resides within=20
the Digital UNIX kernel and is the software interface to a hardware =
device or=20
devices. <A name=3Dnx_id_2></A>A hardware device is a peripheral, such =
as a disk=20
controller, tape controller, or network controller device. In general, =
there is=20
one device driver for each type of hardware device. Device drivers can =
be=20
classified as:=20
<UL>
<P>
<LI>Block device drivers=20
<P></P>
<LI>Character device drivers (including terminal drivers)=20
<P></P>
<LI>Network device drivers=20
<P></P>
<LI>Pseudodevice drivers </LI></UL>
<P>The following sections briefly discuss each type.=20
<BLOCKQUOTE>
<P align=3Dcenter><FONT size=3D+1><STRONG>Note</STRONG></FONT>
<P>This book does not discuss how to write STREAMS device drivers. =
However,=20
<CITE>Writing Device Drivers: Reference</CITE> contains reference =
pages for=20
kernel interfaces that STREAMS device drivers use. See the =
<CITE>Network=20
Programmer's Guide</CITE> for information on STREAMS programming =
frameworks=20
and other information related to STREAMS. </P></BLOCKQUOTE>
<P><A name=3Dblock_devdrv></A>
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<P>
<H3>1.2.1 Block Device Driver </H3>
<P><A name=3Dnx_id_3></A>A block device driver is a driver that performs =
I/O by=20
using file system block-sized buffers from a buffer cache supplied by =
the=20
kernel. The kernel also provides for the device driver support =
interfaces that=20
copy data between the buffer cache and the address space of a process.=20
<P>Block device drivers are particularly well-suited for disk drives, =
the most=20
common block devices. For block devices, all I/O occurs through the =
buffer=20
cache. <A name=3Dnx_id_4></A><A name=3Dchar_devdrv></A>
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