Bring in the ACPI documentation from my local tree. This is mostly

complete, but still needs some work.

en_US.ISO8859-1/books/handbook/config/chapter.sgml

@@ -1658,6 +1658,88 @@ kern.maxfiles: 2088 -> 5000</screen>
       </example>
     </sect2>
   </sect1>
+
+  <sect1 id="acpi-overview">
+    <sect1info>
+      <authorgroup>
+	<author>
+	  <firstname>Hiten</firstname>
+	  <surname>Pandya</surname>
+	  <contrib>Written by </contrib>
+	</author>
+	<author>
+	  <firstname>Tom</firstname>
+	  <surname>Rhodes</surname>
+	</author>
+      </authorgroup>
+    </sect1info>
+    
+    <title>ACPI and FreeBSD</title>
+
+    <para>It is very important to utilize hardware resources in an
+      efficient manner.  Before <acronym>ACPI</acronym> was introduced,
+      it was very difficult and inflexible for operating systems to manage
+      the power usage and thermal properties of a system.  The hardware was
+      either controlled by some sort of <acronym>BIOS</acronym> embedded
+      interface, i.e.: <emphasis>Plug and Play BIOS (PNPBIOS)</emphasis>,
+      <emphasis>Advanced Power Management (APM)</emphasis> and so on.
+      Power and Resource Management is one of the key components of a modern
+      operating system.  For example, you would want an operating system to
+      monitor system limits (and possibly take an action), in case your its
+      temperature increased unexpectedly.</para>
+
+    <para>In this section of the FreeBSD Handbook, we will provide
+      comprehensive information about <acronym>ACPI</acronym>.  References
+      will be provided for further reading, at the end.  Please be aware
+      that <acronym>ACPI</acronym> is only availible on FreeBSD 5.X and
+      above.</para>
+
+    <sect2 id="acpi-intro">
+      <title>What is ACPI?</title>
+
+      <para>Advanced Configuration and Power Interface
+	(<acronym>ACPI</acronym>) is a standard written by
+	an alliance of vendors to provide a standard interface for
+	hardware resources and power management (hence the name).
+	It is a key element in <emphasis>Operating System-directed
+	configuration and Power Management</emphasis>, i.e.: it provides
+	more control and flexibility to the operating system (<acronym>OS</acronym>).
+	Modern systems <quote>stretched</quote> the limits of the current
+	Plug and Play interfaces (such as APM, which is used in FreeBSD 4.X),
+	prior to the introduction of <acronym>ACPI</acronym>.  <acronym>ACPI</acronym>
+	is the direct successor to <acronym>APM</acronym> (Advanced Power
+	Management).</para>
+
+    <sect2 id="acpi-config">
+      <title>Configuring <acronym>ACPI</acronym></title>
+      
+      <para>The <filename>acpi.ko</filename> driver is loaded by the
+	at start up by &man.loader.8; by default and should <emphasis>not</emphasis>
+	be compiled into the kernel.  The reasoning behind this is that modules
+	are easier to work with, say if switching to another <filename>acpi.ko</filename>
+	without doing a kernel rebuild.  This has the advantage of making testing easier.
+	Another reason is that starting <acronym>ACPI</acronym> after a system has been
+	brought up is not to useful, and in some cases can be fatal.  If in doubt, just
+	disable <acronym>ACPI</acronym> all togeather. This driver should not and can not
+	be unloaded because the system bus uses it for various hardware interactions.
+	<acronym>ACPI</acronym> can be disabled with the &man.acpiconf.8; utility.
+	In fact most of the interaction with <acronym>ACPI</acronym> can be done via
+	&man.acpiconf.8;.  Basicly this means, if anything about <acronym>ACPI</acronym>
+	is in the &man.dmesg.8; output, then most likely it is already running.</para>
+
+      <note><para><acronym>ACPI</acronym> and <acronym>APM</acronym> cannot coexist and
+	should be used sperately.  The last one to load will terminate if the driver
+	notices the other running.</para></note>
+
+      <para>In the simpleist form, <acronym>ACPI</acronym> can be used to put the
+	system into a sleep mode with &man.acpiconf.8;, the <option>-s</option>
+	flag, and a <literal>1-5</literal> option.  Most users will only need
+	<literal>1</literal>.  Option <literal>5</literal> will do a soft-off
+	which is the same action as:</para>
+
+      <screen>&prompt.root;<userinput>halt -p</userinput></screen>
+    </sect2>
+  </sect1>
 </chapter>
 
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