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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>usb_set_interface</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="ch05.html" title="Chapter 5. USB Core APIs" /><link rel="prev" href="re69.html" title="usb_reset_endpoint" /><link rel="next" href="re71.html" title="usb_reset_configuration" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span>usb_set_interface</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="re69.html">Prev</a> </td><th width="60%" align="center">Chapter 5. USB Core APIs</th><td width="20%" align="right"> <a accesskey="n" href="re71.html">Next</a></td></tr></table><hr /></div><div class="refentry" title="usb_set_interface"><a id="API-usb-set-interface"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>usb_set_interface —
Makes a particular alternate setting be current
</p></div><div class="refsynopsisdiv" title="Synopsis"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">usb_set_interface </b>(</code></td><td>struct usb_device * <var class="pdparam">dev</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">interface</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">alternate</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Arguments"><a id="id2748420"></a><h2>Arguments</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>dev</code></em></span></dt><dd><p>
the device whose interface is being updated
</p></dd><dt><span class="term"><em class="parameter"><code>interface</code></em></span></dt><dd><p>
the interface being updated
</p></dd><dt><span class="term"><em class="parameter"><code>alternate</code></em></span></dt><dd><p>
the setting being chosen.
</p></dd></dl></div></div><div class="refsect1" title="Context"><a id="id2748480"></a><h2>Context</h2><p>
!in_interrupt ()
</p></div><div class="refsect1" title="Description"><a id="id2748490"></a><h2>Description</h2><p>
This is used to enable data transfers on interfaces that may not
be enabled by default. Not all devices support such configurability.
Only the driver bound to an interface may change its setting.
</p><p>
Within any given configuration, each interface may have several
alternative settings. These are often used to control levels of
bandwidth consumption. For example, the default setting for a high
speed interrupt endpoint may not send more than 64 bytes per microframe,
while interrupt transfers of up to 3KBytes per microframe are legal.
Also, isochronous endpoints may never be part of an
interface's default setting. To access such bandwidth, alternate
interface settings must be made current.
</p><p>
Note that in the Linux USB subsystem, bandwidth associated with
an endpoint in a given alternate setting is not reserved until an URB
is submitted that needs that bandwidth. Some other operating systems
allocate bandwidth early, when a configuration is chosen.
</p><p>
This call is synchronous, and may not be used in an interrupt context.
Also, drivers must not change altsettings while urbs are scheduled for
endpoints in that interface; all such urbs must first be completed
(perhaps forced by unlinking).
</p><p>
Returns zero on success, or else the status code returned by the
underlying <code class="function">usb_control_msg</code> call.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="re69.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch05.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="re71.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span>usb_reset_endpoint</span> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> <span>usb_reset_configuration</span></td></tr></table></div></body></html>
