Add an entry about ``stray IRQ'' messages.

PR:		kern/17774
Submitted by:	Stephen Montgomery-Smith <stephen@math.missouri.edu>

en_US.ISO8859-1/books/faq/book.sgml

@@ -17,7 +17,7 @@
 
     <corpauthor>The FreeBSD Documentation Project</corpauthor>
 
-    <pubdate>$FreeBSD: doc/en_US.ISO8859-1/books/faq/book.sgml,v 1.260 2001/08/31 17:04:49 dd Exp $</pubdate>
+    <pubdate>$FreeBSD: doc/en_US.ISO8859-1/books/faq/book.sgml,v 1.261 2001/09/03 03:09:59 brian Exp $</pubdate>
 
     <copyright>
       <year>1995</year>
@@ -4181,6 +4181,38 @@ IO range check 0x00 activate 0x01</screen>
             your problem.</para>
         </answer>
       </qandaentry>
+
+      <qandaentry>
+        <question id="stray-irq">
+          <para>What does <errorname>stray IRQ</errorname> mean?</para>
+        </question>
+	<answer>
+	  <para>Stray IRQs are indications of hardware IRQ glitches,
+            mostly from hardware that removes its interrupt request in
+            the middle of the interrupt request acknowledge
+            cycle.</para>
+	  <para>One has three options for dealing with this:</para>
+	  <itemizedlist>
+	    <listitem>
+	      <para>Live with the warnings.  All except the first 5
+                per irq are suppressed anyway.</para>
+	    </listitem>
+	    <listitem>
+	      <para>Break the warnings by changing 5 to 0 in
+	        <function>isa_strayintr()</function> so that all the
+	        warnings are suppressed.</para>
+	    </listitem>
+	    <listitem>
+	      <para>Break the warnings by installing parallel port
+              hardware that uses irq 7 and the ppp driver for it (this
+              happens on most systems), and install an ide drive or
+              other hardware that uses irq 15 and a suitable driver
+              for it.</para>
+	    </listitem>
+	  </itemizedlist>
+	</answer>
+      </qandaentry>
+
       <qandaentry>
         <question id="file-table-full">
           <para>Why does <errorname>file: table is full</errorname> show up