introduction to device drivers.htm

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

mounted as a file system and, therefore, does not use data caching. <A 
name=nx_id_9></A><A name=nx_id_10></A><A name=netwrk_devdrv></A>
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<H3>1.2.3&nbsp;&nbsp;&nbsp;&nbsp;Network Device Driver </H3>
<P><A name=nx_id_11></A>A network device driver attaches a network subsystem to 
a network interface, prepares the network interface for operation, and governs 
the transmission and reception of network frames over the network interface. 
This book does not discuss network device drivers. <A name=PseudoDevDrv></A>
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<H3>1.2.4&nbsp;&nbsp;&nbsp;&nbsp;Pseudodevice Driver </H3>
<P><A name=nx_id_12></A>Not all device drivers control physical hardware. Such 
device drivers are called ``pseudodevice'' drivers. Like block and character 
device drivers, pseudodevice drivers make use of the device driver interfaces. 
Unlike block and character device drivers, pseudodevice drivers do not operate 
on a bus. One example of a pseudodevice driver is the pseudoterminal or 
<TT>pty</TT> terminal driver, which simulates a terminal device. The 
<TT>pty</TT> terminal driver is a character device driver typically used for 
remote logins. <A name=nx_id_13></A><A name=static_vs_load_drvs></A>
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<P>
<H2>1.3&nbsp;&nbsp;&nbsp;&nbsp;Single Binary Module </H2>
<P><A name=nx_id_14></A>Digital UNIX provides the tools and techniques for you 
to produce a single binary module. A single binary module is the executable 
image of a device driver that can be statically or dynamically configured into 
the kernel. A single binary module has a file extension of <TT>.mod</TT>. The 
<TT>.mod</TT> file for the current version of Digital UNIX is not the same as 
the <TT>.mod</TT> file used in previous versions of the operating system. 
<P>To produce a single binary module, there is code you need to implement in the 
driver's <TT>configure</TT> interface. <A 
href="http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/HTML/AA-PUBVD-TE_html/drivertut10.html#ImplConfigureRtn">Chapter 
6</A> describes how to write a <TT>configure</TT> interface so that your device 
driver can be statically or dynamically configured into the kernel. In addition, 
there are steps you follow when using the system management tools for statically 
and dynamically configuring the driver (the single binary module) into the 
kernel. <A 
href="http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/HTML/AA-PUBVD-TE_html/drivertut19.html#ConfigModuleDynamicDrv">Chapter 
14</A> explains how to statically and dynamically configure drivers into the 
kernel. <A name=whentocall_devdrv></A>
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<H2>1.4&nbsp;&nbsp;&nbsp;&nbsp;When a Device Driver Is Called </H2>
<P><A 
href="http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/HTML/AA-PUBVD-TE_html/drivertut3.html#whenkerncalls_drv">Figure 
1-1</A> shows that the kernel calls a device driver during: 
<UL>
  <P>
  <LI>Autoconfiguration 
  <P>The kernel calls a device driver (specifically, the driver's <TT>probe</TT> 
  interface) at autoconfiguration time to determine what devices are available 
  and to initialize them. <BR>
  <P></P>
  <LI>I/O operations 
  <P>The kernel calls a device driver to perform I/O operations on the device. 
  These operations include opening the device to perform reads and writes and 
  closing the device. 
  <P></P>
  <LI>Interrupt handling 
  <P>The kernel calls a device driver to handle interrupts from devices capable 
  of generating them. 
  <P></P>
  <LI>Special requests 
  <P>The kernel calls a device driver to handle special requests through 
  <TT>ioctl</TT> calls. 
  <P></P>
  <LI>Reinitialization 
  <P>The kernel calls a device driver to reinitialize the driver, the device, or 
  both when the bus (the path from the CPU to the device) is reset. 
  <P></P>
  <LI>User-level requests to the <TT>sysconfig</TT> utility 
  <P>The kernel calls a device driver (specifically, the driver's 
  <TT>configure</TT> interface) to handle requests that result from use of the 
  <TT>sysconfig</TT> utility. The <TT>sysconfig</TT> utility allows a system 
  manager to dynamically configure, unconfigure, query, and reconfigure a 
  device. These requests cause the kernel to call the device driver's 
  <TT>configure</TT> interface. In addition, the driver's <TT>configure</TT> 
  interface performs one-time initializations when called by the boot software 
  or by the <TT>sysconfig</TT> utility. </P></LI></UL>
<P><A name=whenkerncalls_drv></A>
<H3>Figure 1-1: When the Kernel Calls a Device Driver</H3>
<P><IMG src="Introduction to Device Drivers_files/zk-0200U.gif">
<P><A name=nx_id_15></A>
<P>Some of these requests, such as input or output, result directly or 
indirectly from corresponding system calls in a user program. Other requests, 
such as the calls at autoconfiguration time, do not result from system calls but 
from activities that occur at boot time. <A name=DevDrvIntegationOver></A>
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<H2>1.5&nbsp;&nbsp;&nbsp;&nbsp;Device Driver Configuration </H2>
<P>Device driver configuration consists of the tasks necessary to incorporate 
device drivers into the kernel to make them available to system management and