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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>Constructor</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Writing an ALSA Driver" /><link rel="up" href="ch06.html" title="Chapter 6. Control Interface" /><link rel="prev" href="ch06s05.html" title="Callbacks" /><link rel="next" href="ch06s07.html" title="Change Notification" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Constructor</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch06s05.html">Prev</a> </td><th width="60%" align="center">Chapter 6. Control Interface</th><td width="20%" align="right"> <a accesskey="n" href="ch06s07.html">Next</a></td></tr></table><hr /></div><div class="section" title="Constructor"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="control-interface-constructor"></a>Constructor</h2></div></div></div><p>
When everything is ready, finally we can create a new
control. To create a control, there are two functions to be
called, <code class="function">snd_ctl_new1()</code> and
<code class="function">snd_ctl_add()</code>.
</p><p>
In the simplest way, you can do like this:
</p><div class="informalexample"><pre class="programlisting">
err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip));
if (err < 0)
return err;
</pre></div><p>
where <em class="parameter"><code>my_control</code></em> is the
struct <span class="structname">snd_kcontrol_new</span> object defined above, and chip
is the object pointer to be passed to
kcontrol->private_data
which can be referred to in callbacks.
</p><p>
<code class="function">snd_ctl_new1()</code> allocates a new
<span class="structname">snd_kcontrol</span> instance (that's why the definition
of <em class="parameter"><code>my_control</code></em> can be with
the <em class="parameter"><code>__devinitdata</code></em>
prefix), and <code class="function">snd_ctl_add</code> assigns the given
control component to the card.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch06s05.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch06.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch06s07.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Callbacks </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Change Notification</td></tr></table></div></body></html>
