introduction to device drivers.mht

What is this ``device driver stuff anyway? Here s a very short introduction to the concept.

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<P>
<HR>

<P>
<H3>1.2.2&nbsp;&nbsp;&nbsp;&nbsp;Character Device Driver </H3>
<P><A name=3Dnx_id_5></A>A character device driver does not handle I/O =
through the=20
buffer cache, so it is not tied to a single approach for handling I/O. =
You can=20
use a character device driver for a device such as a line printer that =
handles=20
one character at a time. However, character drivers are not limited to=20
performing I/O one character at a time (despite the name ``character'' =
driver).=20
For example, tape drivers frequently perform I/O in 10K chunks. You can =
also use=20
a character device driver when it is necessary to copy data directly to =
or from=20
a user process. <A name=3Dnx_id_6></A>
<P>Because of their flexibility in handling I/O, many drivers are =
character=20
drivers. Line printers, interactive terminals, and graphics displays are =

examples of devices that require character device drivers.=20
<P><A name=3Dnx_id_7></A><A name=3Dnx_id_8></A>A terminal device driver =
is actually=20
a character device driver that handles I/O character processing for a =
variety of=20
terminal devices. Like any character device, a terminal device can =
accept or=20
supply a stream of data based on a request from a user process. It =
cannot be=20
mounted as a file system and, therefore, does not use data caching. <A=20
name=3Dnx_id_9></A><A name=3Dnx_id_10></A><A name=3Dnetwrk_devdrv></A>
<P>
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<P>
<HR>

<P>
<H3>1.2.3&nbsp;&nbsp;&nbsp;&nbsp;Network Device Driver </H3>
<P><A name=3Dnx_id_11></A>A network device driver attaches a network =
subsystem to=20
a network interface, prepares the network interface for operation, and =
governs=20
the transmission and reception of network frames over the network =
interface.=20
This book does not discuss network device drivers. <A =
name=3DPseudoDevDrv></A>
<P>
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<P>
<H3>1.2.4&nbsp;&nbsp;&nbsp;&nbsp;Pseudodevice Driver </H3>
<P><A name=3Dnx_id_12></A>Not all device drivers control physical =
hardware. Such=20
device drivers are called ``pseudodevice'' drivers. Like block and =
character=20
device drivers, pseudodevice drivers make use of the device driver =
interfaces.=20
Unlike block and character device drivers, pseudodevice drivers do not =
operate=20
on a bus. One example of a pseudodevice driver is the pseudoterminal or=20
<TT>pty</TT> terminal driver, which simulates a terminal device. The=20
<TT>pty</TT> terminal driver is a character device driver typically used =
for=20
remote logins. <A name=3Dnx_id_13></A><A name=3Dstatic_vs_load_drvs></A>
<P>
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<P>
<H2>1.3&nbsp;&nbsp;&nbsp;&nbsp;Single Binary Module </H2>
<P><A name=3Dnx_id_14></A>Digital UNIX provides the tools and techniques =
for you=20
to produce a single binary module. A single binary module is the =
executable=20
image of a device driver that can be statically or dynamically =
configured into=20
the kernel. A single binary module has a file extension of =
<TT>.mod</TT>. The=20
<TT>.mod</TT> file for the current version of Digital UNIX is not the =
same as=20
the <TT>.mod</TT> file used in previous versions of the operating =
system.=20
<P>To produce a single binary module, there is code you need to =
implement in the=20
driver's <TT>configure</TT> interface. <A=20
href=3D"http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/HTML/AA-PUB=
VD-TE_html/drivertut10.html#ImplConfigureRtn">Chapter=20
6</A> describes how to write a <TT>configure</TT> interface so that your =
device=20
driver can be statically or dynamically configured into the kernel. In =
addition,=20
there are steps you follow when using the system management tools for =
statically=20
and dynamically configuring the driver (the single binary module) into =
the=20
kernel. <A=20
href=3D"http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/HTML/AA-PUB=
VD-TE_html/drivertut19.html#ConfigModuleDynamicDrv">Chapter=20
14</A> explains how to statically and dynamically configure drivers into =
the=20
kernel. <A name=3Dwhentocall_devdrv></A>
<P>
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