Update of /cvsroot/alsa/alsa-kernel/Documentation/DocBook
In directory sc8-pr-cvs1:/tmp/cvs-serv7949/DocBook
Modified Files:
writing-an-alsa-driver.tmpl
Log Message:
added more texts about hw_constraints by Guiliano.
Index: writing-an-alsa-driver.tmpl
===================================================================
RCS file: /cvsroot/alsa/alsa-kernel/Documentation/DocBook/writing-an-alsa-driver.tmpl,v
retrieving revision 1.9
retrieving revision 1.10
diff -u -r1.9 -r1.10
--- writing-an-alsa-driver.tmpl 16 May 2003 09:06:04 -0000 1.9
+++ writing-an-alsa-driver.tmpl 2 Jun 2003 12:58:04 -0000 1.10
@@ -2906,7 +2906,8 @@
</para>
<para>
- This callback may be called multiple times, too.
+ This function is always called before the close callback is called.
+ Also, the callback may be called multiple times, too.
Keep track whether the resource was already released.
</para>
</section>
@@ -3007,14 +3008,16 @@
</para>
<para>
- When the pcm supports the suspend/resume operation,
+ When the pcm supports the suspend/resume operation
+ (i.e. <constant>SNDRV_PCM_INFO_RESUME</constant> flag is set),
<constant>SUSPEND</constant> and <constant>RESUME</constant>
- commands must be handled, too. Obviously it does suspend and
- resume of the pcm substream. Usually, the
- <constant>SUSPEND</constant> is identical with
- <constant>STOP</constant> command and the
- <constant>RESUME</constant> is identical with
- <constant>START</constant> command.
+ commands must be handled, too.
+ These commands are issued when the power-management status is
+ changed. Obviously, the <constant>SUSPEND</constant> and
+ <constant>RESUME</constant>
+ do suspend and resume of the pcm substream, and usually, they
+ are identical with <constant>STOP</constant> and
+ <constant>START</constant> commands, respectively.
</para>
<para>
@@ -3331,9 +3334,96 @@
</para>
<para>
- There are many different constraints. You can even define your
- own constraint rules. I won't explain the details here, rather I
- would like to say, <quote>Luke, use the source.</quote>
+ There are many different constraints.
+ Look in <filename>sound/asound.h</filename> for a complete list.
+ You can even define your own constraint rules.
+ For example, let's suppose my_chip can manage a substream of 1 channel
+ if and only if the format is S16_LE, otherwise it supports any format
+ specified in the <type>snd_pcm_hardware_t</type> stucture (or in any
+ other constraint_list). You can build a rule like this:
+
+ <example>
+ <title>Example of Hardware Constraints for Channels</title>
+ <programlisting>
+<![CDATA[
+ static int hw_rule_format_by_channels(snd_pcm_hw_params_t *params,
+ snd_pcm_hw_rule_t *rule)
+ {
+ snd_interval_t *c = hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
+ snd_mask_t *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
+ snd_mask_t fmt;
+
+ snd_mask_any(&fmt); // Init the struct
+ if (c->min < 2) {
+ fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE;
+ return snd_mask_refine(f, &fmt);
+ }
+ return 0;
+ }
+]]>
+ </programlisting>
+ </example>
+ </para>
+
+ <para>
+ Then you need to call this function to add your rule:
+
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
+ hw_rule_channels_by_format, 0, SNDRV_PCM_HW_PARAM_FORMAT,
+ -1);
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+
+ <para>
+ The rule function is called when an application sets the number of
+ channels. But an application can set the format before the number of
+ channels. Thus you also need to define the inverse rule:
+
+ <example>
+ <title>Example of Hardware Constraints for Channels</title>
+ <programlisting>
+<![CDATA[
+ static int hw_rule_channels_by_format(snd_pcm_hw_params_t *params,
+ snd_pcm_hw_rule_t *rule)
+ {
+ snd_interval_t *c = hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
+ snd_mask_t *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
+ snd_interval_t ch;
+
+ snd_interval_any(&ch);
+ if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) {
+ ch.min = ch.max = 1;
+ ch.integer = 1;
+ return snd_interval_refine(c, &ch);
+ }
+ return 0;
+ }
+]]>
+ </programlisting>
+ </example>
+ </para>
+
+ <para>
+ ...and in the open callback:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
+ hw_rule_format_by_channels, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
+ -1);
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+
+ <para>
+ I won't explain more details here, rather I
+ would like to say, <quote>Luke, use the source.</quote>
</para>
</section>
@@ -5755,6 +5845,10 @@
<para>
Kevin Conder reformatted the original plain-text to the
DocBook format.
+ </para>
+ <para>
+ Giuliano Pochini corrected typos and contributed the example codes
+ in the hardware constraints section.
</para>
</chapter>
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