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authorClemens Ladisch <clemens@ladisch.de>2007-09-10 02:05:19 -0400
committerJaroslav Kysela <perex@perex.cz>2007-10-16 10:49:17 -0400
commitd1761d1b14158498d4782d555a9b367ea4647224 (patch)
tree85abe818de9c6771f89344acdf4fe99f0bfb0f3f
parent950fb626dc28e17ae4ad01dba07957bdc6e0b997 (diff)
[ALSA] document basic TLV stuff
Add documentation about how to define dB scale information for mixer controls. Signed-off-by: Clemens Ladisch <clemens@ladisch.de> Signed-off-by: Jaroslav Kysela <perex@suse.cz>
-rw-r--r--Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl61
1 files changed, 59 insertions, 2 deletions
diff --git a/Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl b/Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl
index b9d2dbee9bc3..2c3fc3cb3b6b 100644
--- a/Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl
+++ b/Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl
@@ -18,8 +18,8 @@
18 </affiliation> 18 </affiliation>
19 </author> 19 </author>
20 20
21 <date>July 26, 2007</date> 21 <date>September 10, 2007</date>
22 <edition>0.3.6.1</edition> 22 <edition>0.3.7</edition>
23 23
24 <abstract> 24 <abstract>
25 <para> 25 <para>
@@ -3473,6 +3473,13 @@ struct _snd_pcm_runtime {
3473 </para> 3473 </para>
3474 3474
3475 <para> 3475 <para>
3476 The <structfield>tlv</structfield> field can be used to provide
3477 metadata about the control; see the
3478 <link linkend="control-interface-tlv">
3479 <citetitle>Metadata</citetitle></link> subsection.
3480 </para>
3481
3482 <para>
3476 The other three are 3483 The other three are
3477 <link linkend="control-interface-callbacks"><citetitle> 3484 <link linkend="control-interface-callbacks"><citetitle>
3478 callback functions</citetitle></link>. 3485 callback functions</citetitle></link>.
@@ -3871,6 +3878,56 @@ struct _snd_pcm_runtime {
3871 </para> 3878 </para>
3872 </section> 3879 </section>
3873 3880
3881 <section id="control-interface-tlv">
3882 <title>Metadata</title>
3883 <para>
3884 To provide information about the dB values of a mixer control, use
3885 on of the <constant>DECLARE_TLV_xxx</constant> macros from
3886 <filename>&lt;sound/tlv.h&gt;</filename> to define a variable
3887 containing this information, set the<structfield>tlv.p
3888 </structfield> field to point to this variable, and include the
3889 <constant>SNDRV_CTL_ELEM_ACCESS_TLV_READ</constant> flag in the
3890 <structfield>access</structfield> field; like this:
3891 <informalexample>
3892 <programlisting>
3893<![CDATA[
3894 static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0);
3895
3896 static struct snd_kcontrol_new my_control __devinitdata = {
3897 ...
3898 .access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
3899 SNDRV_CTL_ELEM_ACCESS_TLV_READ,
3900 ...
3901 .tlv.p = db_scale_my_control,
3902 };
3903]]>
3904 </programlisting>
3905 </informalexample>
3906 </para>
3907
3908 <para>
3909 The <function>DECLARE_TLV_DB_SCALE</function> macro defines
3910 information about a mixer control where each step in the control's
3911 value changes the dB value by a constant dB amount.
3912 The first parameter is the name of the variable to be defined.
3913 The second parameter is the minimum value, in units of 0.01 dB.
3914 The third parameter is the step size, in units of 0.01 dB.
3915 Set the fourth parameter to 1 if the minimum value actually mutes
3916 the control.
3917 </para>
3918
3919 <para>
3920 The <function>DECLARE_TLV_DB_LINEAR</function> macro defines
3921 information about a mixer control where the control's value affects
3922 the output linearly.
3923 The first parameter is the name of the variable to be defined.
3924 The second parameter is the minimum value, in units of 0.01 dB.
3925 The third parameter is the maximum value, in units of 0.01 dB.
3926 If the minimum value mutes the control, set the second parameter to
3927 <constant>TLV_DB_GAIN_MUTE</constant>.
3928 </para>
3929 </section>
3930
3874 </chapter> 3931 </chapter>
3875 3932
3876 3933