<?xml version="1.0" encoding="ANSI_X3.4-1968" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>struct usb_host_config</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="The Linux-USB Host Side API" /><link rel="up" href="ch04.html" title="Chapter 4. Host-Side Data Types and Macros" /><link rel="prev" href="re19.html" title="struct usb_interface_cache" /><link rel="next" href="re21.html" title="struct usb_device" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span>struct usb_host_config</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="re19.html">Prev</a> </td><th width="60%" align="center">Chapter 4. Host-Side Data Types and Macros</th><td width="20%" align="right"> <a accesskey="n" href="re21.html">Next</a></td></tr></table><hr /></div><div class="refentry" title="struct usb_host_config"><a id="API-struct-usb-host-config"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>struct usb_host_config —
representation of a device's configuration
</p></div><div class="refsynopsisdiv" title="Synopsis"><h2>Synopsis</h2><pre class="programlisting">
struct usb_host_config {
struct usb_config_descriptor desc;
char * string;
struct usb_interface_assoc_descriptor * intf_assoc[USB_MAXIADS];
struct usb_interface * interface[USB_MAXINTERFACES];
struct usb_interface_cache * intf_cache[USB_MAXINTERFACES];
unsigned char * extra;
int extralen;
}; </pre></div><div class="refsect1" title="Members"><a id="id3102404"></a><h2>Members</h2><div class="variablelist"><dl><dt><span class="term">desc</span></dt><dd><p>
the device's configuration descriptor.
</p></dd><dt><span class="term">string</span></dt><dd><p>
pointer to the cached version of the iConfiguration string, if
present for this configuration.
</p></dd><dt><span class="term">intf_assoc[USB_MAXIADS]</span></dt><dd><p>
list of any interface association descriptors in this config
</p></dd><dt><span class="term">interface[USB_MAXINTERFACES]</span></dt><dd><p>
array of pointers to usb_interface structures, one for each
interface in the configuration. The number of interfaces is stored
in desc.bNumInterfaces. These pointers are valid only while the
the configuration is active.
</p></dd><dt><span class="term">intf_cache[USB_MAXINTERFACES]</span></dt><dd><p>
array of pointers to usb_interface_cache structures, one
for each interface in the configuration. These structures exist
for the entire life of the device.
</p></dd><dt><span class="term">extra</span></dt><dd><p>
pointer to buffer containing all extra descriptors associated
with this configuration (those preceding the first interface
descriptor).
</p></dd><dt><span class="term">extralen</span></dt><dd><p>
length of the extra descriptors buffer.
</p></dd></dl></div></div><div class="refsect1" title="Description"><a id="id3102505"></a><h2>Description</h2><p>
USB devices may have multiple configurations, but only one can be active
at any time. Each encapsulates a different operational environment;
for example, a dual-speed device would have separate configurations for
full-speed and high-speed operation. The number of configurations
available is stored in the device descriptor as bNumConfigurations.
</p><p>
A configuration can contain multiple interfaces. Each corresponds to
a different function of the USB device, and all are available whenever
the configuration is active. The USB standard says that interfaces
are supposed to be numbered from 0 to desc.bNumInterfaces-1, but a lot
of devices get this wrong. In addition, the interface array is not
guaranteed to be sorted in numerical order. Use <code class="function">usb_ifnum_to_if</code> to
look up an interface entry based on its number.
</p><p>
Device drivers should not attempt to activate configurations. The choice
of which configuration to install is a policy decision based on such
considerations as available power, functionality provided, and the user's
desires (expressed through userspace tools). However, drivers can call
<code class="function">usb_reset_configuration</code> to reinitialize the current configuration and
all its interfaces.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="re19.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch04.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="re21.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span>struct usb_interface_cache</span> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> <span>struct usb_device</span></td></tr></table></div></body></html>
