Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=d1761d1b14158498d4782d555a9b367ea4647224
Commit: d1761d1b14158498d4782d555a9b367ea4647224
Parent: 950fb626dc28e17ae4ad01dba07957bdc6e0b997
Author: Clemens Ladisch <[EMAIL PROTECTED]>
AuthorDate: Mon Sep 10 08:05:19 2007 +0200
Committer: Jaroslav Kysela <[EMAIL PROTECTED]>
CommitDate: Tue Oct 16 16:49:17 2007 +0200
[ALSA] document basic TLV stuff
Add documentation about how to define dB scale information for mixer
controls.
Signed-off-by: Clemens Ladisch <[EMAIL PROTECTED]>
Signed-off-by: Jaroslav Kysela <[EMAIL PROTECTED]>
---
.../sound/alsa/DocBook/writing-an-alsa-driver.tmpl | 61 +++++++++++++++++++-
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 b9d2dbe..2c3fc3c 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 @@
</affiliation>
</author>
- <date>July 26, 2007</date>
- <edition>0.3.6.1</edition>
+ <date>September 10, 2007</date>
+ <edition>0.3.7</edition>
<abstract>
<para>
@@ -3473,6 +3473,13 @@ struct _snd_pcm_runtime {
</para>
<para>
+ The <structfield>tlv</structfield> field can be used to provide
+ metadata about the control; see the
+ <link linkend="control-interface-tlv">
+ <citetitle>Metadata</citetitle></link> subsection.
+ </para>
+
+ <para>
The other three are
<link linkend="control-interface-callbacks"><citetitle>
callback functions</citetitle></link>.
@@ -3871,6 +3878,56 @@ struct _snd_pcm_runtime {
</para>
</section>
+ <section id="control-interface-tlv">
+ <title>Metadata</title>
+ <para>
+ To provide information about the dB values of a mixer control, use
+ on of the <constant>DECLARE_TLV_xxx</constant> macros from
+ <filename><sound/tlv.h></filename> to define a variable
+ containing this information, set the<structfield>tlv.p
+ </structfield> field to point to this variable, and include the
+ <constant>SNDRV_CTL_ELEM_ACCESS_TLV_READ</constant> flag in the
+ <structfield>access</structfield> field; like this:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0);
+
+ static struct snd_kcontrol_new my_control __devinitdata = {
+ ...
+ .access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+ SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+ ...
+ .tlv.p = db_scale_my_control,
+ };
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+
+ <para>
+ The <function>DECLARE_TLV_DB_SCALE</function> macro defines
+ information about a mixer control where each step in the control's
+ value changes the dB value by a constant dB amount.
+ The first parameter is the name of the variable to be defined.
+ The second parameter is the minimum value, in units of 0.01 dB.
+ The third parameter is the step size, in units of 0.01 dB.
+ Set the fourth parameter to 1 if the minimum value actually mutes
+ the control.
+ </para>
+
+ <para>
+ The <function>DECLARE_TLV_DB_LINEAR</function> macro defines
+ information about a mixer control where the control's value affects
+ the output linearly.
+ The first parameter is the name of the variable to be defined.
+ The second parameter is the minimum value, in units of 0.01 dB.
+ The third parameter is the maximum value, in units of 0.01 dB.
+ If the minimum value mutes the control, set the second parameter to
+ <constant>TLV_DB_GAIN_MUTE</constant>.
+ </para>
+ </section>
+
</chapter>
-
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