1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>Components</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Writing an ALSA Driver"><link rel="up" href="card-management.html" title="Chapter 3. Management of Cards and Components"><link rel="prev" href="card-management.html" title="Chapter 3. Management of Cards and Components"><link rel="next" href="card-management-chip-specific.html" title="Chip-Specific Data"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Components</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="card-management.html">Prev</a> </td><th width="60%" align="center">Chapter 3. Management of Cards and Components</th><td width="20%" align="right"> <a accesskey="n" href="card-management-chip-specific.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="card-management-component"></a>Components</h2></div></div></div><p> 2 After the card is created, you can attach the components 3 (devices) to the card instance. In an ALSA driver, a component is 4 represented as a struct <span class="structname">snd_device</span> object. 5 A component can be a PCM instance, a control interface, a raw 6 MIDI interface, etc. Each such instance has one component 7 entry. 8 </p><p> 9 A component can be created via 10 <code class="function">snd_device_new()</code> function. 11 12 </p><div class="informalexample"><pre class="programlisting"> 13 14 snd_device_new(card, SNDRV_DEV_XXX, chip, &ops); 15 16 </pre></div><p> 17 </p><p> 18 This takes the card pointer, the device-level 19 (<code class="constant">SNDRV_DEV_XXX</code>), the data pointer, and the 20 callback pointers (<em class="parameter"><code>&ops</code></em>). The 21 device-level defines the type of components and the order of 22 registration and de-registration. For most components, the 23 device-level is already defined. For a user-defined component, 24 you can use <code class="constant">SNDRV_DEV_LOWLEVEL</code>. 25 </p><p> 26 This function itself doesn't allocate the data space. The data 27 must be allocated manually beforehand, and its pointer is passed 28 as the argument. This pointer (<em class="parameter"><code>chip</code></em> in the 29 above example) is used as the identifier for the instance. 30 </p><p> 31 Each pre-defined ALSA component such as ac97 and pcm calls 32 <code class="function">snd_device_new()</code> inside its 33 constructor. The destructor for each component is defined in the 34 callback pointers. Hence, you don't need to take care of 35 calling a destructor for such a component. 36 </p><p> 37 If you wish to create your own component, you need to 38 set the destructor function to the dev_free callback in 39 the <em class="parameter"><code>ops</code></em>, so that it can be released 40 automatically via <code class="function">snd_card_free()</code>. 41 The next example will show an implementation of chip-specific 42 data. 43 </p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="card-management.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="card-management.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="card-management-chip-specific.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 3. Management of Cards and Components </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chip-Specific Data</td></tr></table></div></body></html> 44