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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>Updating Registers in The Driver</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="ch07.html" title="Chapter 7. API for AC97 Codec" /><link rel="prev" href="ch07s04.html" title="Callbacks" /><link rel="next" href="ch07s06.html" title="Clock Adjustment" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Updating Registers in The Driver</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch07s04.html">Prev</a> </td><th width="60%" align="center">Chapter 7. API for AC97 Codec</th><td width="20%" align="right"> <a accesskey="n" href="ch07s06.html">Next</a></td></tr></table><hr /></div><div class="section" title="Updating Registers in The Driver"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="api-ac97-updating-registers"></a>Updating Registers in The Driver</h2></div></div></div><p>
If you need to access to the codec from the driver, you can
call the following functions:
<code class="function">snd_ac97_write()</code>,
<code class="function">snd_ac97_read()</code>,
<code class="function">snd_ac97_update()</code> and
<code class="function">snd_ac97_update_bits()</code>.
</p><p>
Both <code class="function">snd_ac97_write()</code> and
<code class="function">snd_ac97_update()</code> functions are used to
set a value to the given register
(<code class="constant">AC97_XXX</code>). The difference between them is
that <code class="function">snd_ac97_update()</code> doesn't write a
value if the given value has been already set, while
<code class="function">snd_ac97_write()</code> always rewrites the
value.
</p><div class="informalexample"><pre class="programlisting">
snd_ac97_write(ac97, AC97_MASTER, 0x8080);
snd_ac97_update(ac97, AC97_MASTER, 0x8080);
</pre></div><p>
</p><p>
<code class="function">snd_ac97_read()</code> is used to read the value
of the given register. For example,
</p><div class="informalexample"><pre class="programlisting">
value = snd_ac97_read(ac97, AC97_MASTER);
</pre></div><p>
</p><p>
<code class="function">snd_ac97_update_bits()</code> is used to update
some bits in the given register.
</p><div class="informalexample"><pre class="programlisting">
snd_ac97_update_bits(ac97, reg, mask, value);
</pre></div><p>
</p><p>
Also, there is a function to change the sample rate (of a
given register such as
<code class="constant">AC97_PCM_FRONT_DAC_RATE</code>) when VRA or
DRA is supported by the codec:
<code class="function">snd_ac97_set_rate()</code>.
</p><div class="informalexample"><pre class="programlisting">
snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100);
</pre></div><p>
</p><p>
The following registers are available to set the rate:
<code class="constant">AC97_PCM_MIC_ADC_RATE</code>,
<code class="constant">AC97_PCM_FRONT_DAC_RATE</code>,
<code class="constant">AC97_PCM_LR_ADC_RATE</code>,
<code class="constant">AC97_SPDIF</code>. When
<code class="constant">AC97_SPDIF</code> is specified, the register is
not really changed but the corresponding IEC958 status bits will
be updated.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch07s04.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch07.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch07s06.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"> Clock Adjustment</td></tr></table></div></body></html>
