Index: io.sgml
===================================================================
RCS file: /cvs/ecos/ecos/packages/io/common/current/doc/io.sgml,v
retrieving revision 1.2
diff -u -r1.2 io.sgml
--- io.sgml	15 Sep 2002 22:10:40 -0000	1.2
+++ io.sgml	5 Aug 2003 15:23:07 -0000
@@ -1143,6 +1143,47 @@
 etc.
 </PARA>
 
+  <funcsynopsis>
+    <funcprototype>
+      <funcdef>Cyg_ErrNo <function>(*lookup)</function></funcdef>
+      <paramdef>struct <parameter>cyg_devtab_entry</parameter> **tab</paramdef>
+      <paramdef>struct <parameter>cyg_devtab_entry</parameter> *sub_tab</paramdef>
+      <paramdef>const char <parameter>name</parameter> *name</paramdef>
+    </funcprototype>
+  </funcsynopsis>
+
+  <para>
+    The lookup function is called from <function>cyg_io_lookup</function>
+    if the name of the device in question (as declared in the
+    corresponding <structname>DEVTAB_ENTRY</structname>) matches the name
+    passed to <function>cyg_io_lookup</function>.
+  </para>
+
+  <para>
+    The <parameter>**tab</parameter> parameter holds a pointer to the
+    memory location of the devtab entry.  This indirection allows the
+    device driver author to create a new devtab entry in the lookup
+    function, in order to provide for pluggable devices, and devices
+    where multiple instances are possible.
+  </para>
+
+  <para>
+    The <parameter>*sub_tab</parameter> parameter is a
+    <type>cyg_io_handle_t</type> that references a second device that
+    the current driver depends on.  It has already been looked up by
+    the time it is passed to the <function>lookup</function> function.
+  </para>
+
+  <para>
+    The <parameter>*name</parameter> parameter holds a pointer to the
+    part of a string passed to <function>cyg_io_lookup</function> that
+    differs from the "base name" of a device.  For instance, a device
+    might have the base name "/dev/fd".  If a lookup is performed on
+    "/dev/fd/1", then the <function>lookup</function> function will be
+    called with "/1" in its <parameter>name</parameter> argument.
+  </para>
+
+
 <!-- }}} -->
 <!-- {{{ How to Write a Serial Hardware Interface Driver -->