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<HTML>
<HEAD>
<TITLE>Advanced Linux Sound Architecture - Driver: Mixer</TITLE>
</HEAD>
<BODY>
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<H2><A NAME="s4">4. Mixer</A></H2>
<P>Mixer related structures and function is in <I>include/mixer.h</I> header
file.</P>
<H2><A NAME="ss4.1">4.1 Variables and functions</A></H2>
<P>Variables from <I>snd_kmixer_t</I> structure which must be filled:</P>
<P>
<UL>
<LI><B>name</B> is name of mixer (for example 'AD1848').</LI>
<LI><B>hw</B> read-only variables dependend on hardware.</LI>
</UL>
</P>
<P>Variables from <I>snd_kmixer_t</I> structure which should be filled:</P>
<P>
<UL>
<LI><B>private_data</B> should contains private data for mixer.</LI>
<LI><B>private_free</B> should free private data.</LI>
</UL>
</P>
<P>Variables from <I>struct snd_stru_mixer_hw</I> structure which must be filled:</P>
<P>
<UL>
<LI><B>caps</B> mixer capabilities (see to <B>SND_SND_MIXER_INFO_CAP_*</B>).</LI>
</UL>
</P>
<P>Variables from <I>struct snd_stru_mixer_hw</I> structure which should be filled:</P>
<P>
<UL>
<LI><B>get_special</B></LI>
<LI><B>set_special</B></LI>
</UL>
</P>
<P>Variables from <I>snd_kmixer_channel_t</I> structure which must be filled:</P>
<P>
<UL>
<LI><B>hw</B> read-only variables dependend on hardware.</LI>
</UL>
</P>
<P>Variables from <I>snd_kmixer_channel_t</I> structure which should be filled:</P>
<P>
<UL>
<LI><B>private_value</B> is <I>unsigned int</I> variable which isn't used
by middle-level code.</LI>
<LI><B>private_data</B> is pointer to some private data associated with
appropriate channel. These data aren't freed by middle-level code.</LI>
</UL>
</P>
<P>Variables from <I>struct snd_stru_mixer_channel_hw</I> structure which must
be filled:</P>
<P>
<UL>
<LI><B>priority</B> priority (identificator) - see to <B>SND_MIXER_PRI_*</B></LI>
<LI><B>parent_priority</B> parent mixer channel priority or <B>SND_MIXER_PRI_PARENT</B></LI>
<LI><B>name</B> name of this mixer channel - see to <B>SND_MIXER_ID_*</B></LI>
<LI><B>ossdev</B> OSS (Open Sound System) device - see to <B>SND_MIXER_OSS_*</B></LI>
<LI><B>mute</B> if hardware mute is supported</LI>
<LI><B>stereo</B> if stereo is supported</LI>
<LI><B>record</B> is recording is possible from this channel</LI>
<LI><B>digital</B> is this channel is digitaly (not analog) mixed</LI>
<LI><B>input</B> is channel is input channel</LI>
<LI><B>min, max</B> specifies exact linear range from <I>min</I> to <I>max</I></LI>
<LI><B>min_dB, max_dB, step_dB</B> range and step size for decibel * 100</LI>
<LI><B>void (*set_record_source)( snd_kmixer_t *mixer, snd_kmixer_channel_t *channel, int enable )</B>
<UL>
<LI><B>mixer</B> pointer to mixer structure</LI>
<LI><B>channel</B> pointer to channel structure</LI>
<LI><B>enable</B> if non-zero - record source must be enabled</LI>
<LI>must be set, if channel supports recording</LI>
</UL>
</LI>
<LI><B>void (*set_mute)( snd_kmixer_t *mixer, snd_kmixer_channel_t *channel, unsigned int mute )</B>
<UL>
<LI><B>mixer</B> pointer to mixer structure</LI>
<LI><B>channel</B> pointer to channel structure</LI>
<LI><B>mute</B> should be zero (no mute) or <B>SND_MIX_MUTE*</B></LI>
<LI>must be set, if channel supports hardware muting</LI>
</UL>
</LI>
<LI><B>void (*set_volume_level)( snd_kmixer_t *mixer, snd_kmixer_channel_t *channel, int left, int right )</B>
<UL>
<LI><B>mixer</B> pointer to mixer structure</LI>
<LI><B>channel</B> pointer to channel structure</LI>
<LI><B>left</B> volume level in exact range</LI>
<LI><B>right</B> volume level in exact range</LI>
<LI>handler which sets volume level for this channel</LI>
</UL>
</LI>
</UL>
</P>
<P>Variables from <I>struct snd_stru_mixer_channel_hw</I> structure which should
be filled:</P>
<P>
<UL>
<LI><B>int (*compute_linear)( snd_kmixer_t *mixer, snd_kmixer_channel_t *channel, int dB )</B>
<UL>
<LI>input = dB from application, output = min...max (linear volume)</LI>
</UL>
</LI>
<LI><B>int (*compute_dB)( snd_kmixer_t *mixer, snd_kmixer_channel_t *channel, int volume )</B>
<UL>
<LI>input = min...max (linear volume), output = dB to application</LI>
</UL>
</LI>
</UL>
</P>
<P>Functions list:</P>
<P>
<UL>
<LI><B>void snd_mixer_set_kernel_mute( snd_kmixer_t *mixer, unsigned int priority, unsigned short mute )</B>
<UL>
<LI><B>mixer</B> pointer to mixer structure</LI>
<LI><B>priority</B> specifies mixer channel</LI>
<LI><B>mute</B> zero or <B>SND_MIX_MUTE*</B></LI>
<LI>should be use as mute control from kernel</LI>
<LI>this settings is never overriden by application</LI>
</UL>
</LI>
<LI><B>snd_kmixer_t *snd_mixer_new( snd_card_t *card, char *id )</B>
<UL>
<LI><B>card</B> pointer to soundcard structure</LI>
<LI><B>id</B> is identification of code (for example 'AD1848').</LI>
</UL>
</LI>
<LI><B>int snd_mixer_free( snd_kmixer_t *mixer )</B>
<UL>
<LI><B>mixer</B> pointer to mixer structure</LI>
<LI>frees mixer structure and private data</LI>
</UL>
</LI>
<LI><B>snd_kmixer_channel_t *snd_mixer_new_channel( snd_kmixer_t *mixer, struct snd_stru_mixer_channel_hw *hw )</B>
<UL>
<LI><B>mixer</B> pointer to mixer structure</LI>
<LI><B>hw</B> pointer to mixer channel variables and operations</LI>
<LI>creates new mixer channel</LI>
</UL>
</LI>
<LI><B>void snd_mixer_reorder_channel( snd_kmixer_t *mixer, snd_kmixer_channel_t *channel )</B>
<UL>
<LI><B>mixer</B> pointer to mixer structure</LI>
<LI><B>channel</B> pointer to mixer channel</LI>
<LI>reorders mixer channels if channel -> priority was changed</LI>
</UL>
</LI>
<LI><B>int snd_mixer_register( snd_kmixer_t *mixer, int device )</B>
<UL>
<LI><B>mixer</B> pointer to mixer structure</LI>
<LI><B>device</B> device number (0-1)</LI>
<LI>registers specified mixer</LI>
</UL>
</LI>
<LI><B>int snd_mixer_unregister( snd_mixer_t *mixer )</B>
<UL>
<LI><B>mixer</B> pointer to mixer structure</LI>
<LI>unregisters and <B>frees</B> specified mixer</LI>
</UL>
</LI>
</UL>
</P>
<H2><A NAME="ss4.2">4.2 Exaples</A></H2>
<P>
<BLOCKQUOTE><CODE>
<HR>
<PRE>
#define CS4231_MIXS (sizeof(snd_cs4231_mixs)/sizeof(struct snd_stru_mixer_channel_hw))
#define CS4231_PRIVATE( left, right, shift, mute ) ((left << 24)|(right << 16)|(shift<<8)|mute)
static struct snd_stru_mixer_channel_hw snd_cs4231_mixs[] = {
{
SND_MIXER_PRI_GAIN, /* priority */
SND_MIXER_PRI_PARENT, /* parent priority */
SND_MIXER_ID_GAIN, /* device name */
SND_MIXER_OSS_IMIX, /* OSS device # */
0, 1, 0, 0, 1, /* mute/stereo/record/digital/input */
0, 15, /* min, max value */
0, 2250, 150, /* min, max, step - dB */
CS4231_PRIVATE( CS4231_LEFT_INPUT, CS4231_RIGHT_INPUT, 0, 0x00 ) | 0x2000,
NULL, /* compute dB -> linear */
NULL, /* compute linear -> dB */
NULL, /* record source */
NULL, /* set mute */
snd_cs4231_volume_level, /* set volume level */
},
....
};
snd_kmixer_t *snd_cs4231_new_mixer( snd_pcm_t *pcm )
{
int idx;
cs4231_t *codec;
snd_kmixer_t *mixer;
snd_kmixer_channel_t *channel;
if ( !pcm || !pcm -> card ) return NULL;
codec = (cs4231_t *)pcm -> private_data;
if ( !codec ) return NULL;
mixer = snd_mixer_new( pcm -> card, pcm -> id );
if ( !mixer ) return NULL;
strcpy( mixer -> name, pcm -> name );
for ( idx = 0; idx < CS4231_MIXS; idx++ ) {
channel = snd_mixer_new_channel( mixer, &snd_cs4231_mixs[ idx ] );
if ( !channel ) {
snd_mixer_free( mixer );
return NULL;
}
}
mixer -> hw.caps = SND_MIXER_INFO_CAP_EXCL_RECORD;
mixer -> private_data = codec;
codec -> mixer = mixer;
return mixer;
}
</PRE>
<HR>
</CODE></BLOCKQUOTE>
</P>
<P>Do you need modify some default mixer channel assignment?</P>
<P>
<BLOCKQUOTE><CODE>
<HR>
<PRE>
snd_kmixer_channel_t *channel;
/* ok. InterWave have MIC different (stereo) */
channel = snd_mixer_find_channel( mixer, SND_MIXER_PRI_MIC );
channel -> hw.stereo = 1;
channel -> hw.max = 31;
channel -> hw.private_value = CS4231_PRIVATE( CS4231_LEFT_MIC_INPUT, CS4231_RIGHT_MIC_INPUT, 0, 0x80 );
/* reassign AUXA to SYNTHESIZER */
channel = snd_mixer_find_channel( mixer, SND_MIXER_PRI_AUXA );
channel -> hw.priority = SND_MIXER_PRI_SYNTHESIZER;
channel -> hw.ossdev = SND_MIXER_OSS_SYNTH;
strcpy( channel -> hw.name, SND_MIXER_ID_SYNTHESIZER );
snd_mixer_reorder_channel( mixer, channel );
</PRE>
<HR>
</CODE></BLOCKQUOTE>
</P>
<P>Do you need add some mixer channel to generic mixer?</P>
<P>
<BLOCKQUOTE><CODE>
<HR>
<PRE>
static struct snd_stru_mixer_channel_hw master = {
SND_MIXER_PRI_MASTER, /* priority */
SND_MIXER_PRI_PARENT, /* parent priority */
SND_MIXER_ID_MASTER, /* device name */
SND_MIXER_OSS_VOLUME, /* OSS device # */
1, 1, 1, 0, 0, /* mute/stereo/record/digital */
0, 31, /* max. value */
-3450, 1200, 150, /* min, max, step - dB */
CS4231_PRIVATE( CS4231_LINE_LEFT_OUTPUT, CS4231_LINE_RIGHT_OUTPUT, 0, 0x80
NULL, /* compute dB -> linear */
NULL, /* compute linear -> dB */
NULL, /* record source */
NULL, /* set mute */
NULL, /* set volume level */
};
int idx;
/* make master as parent */
for ( idx = 0; idx < mixer -> channels_count; idx++ ) {
channel = mixer -> channels[ idx ];
if ( !channel -> hw.input )
channel -> hw.parent_priority = SND_MIXER_PRI_MASTER;
}
/* add master volume control */
master.set_record_source = channel -> hw.set_record_source;
master.set_mute = channel -> hw.set_mute;
master.set_volume_level = channel -> hw.set_volume_level;
channel = snd_mixer_new_channel( mixer, &master );
if ( !channel ) return -ENOMEM;
</PRE>
<HR>
</CODE></BLOCKQUOTE>
</P>
<P>Mixer device registering:</P>
<P>
<BLOCKQUOTE><CODE>
<HR>
<PRE>
snd_card_t *card;
snd_pcm_t *pcm.
snd_kmixer_t *mixer;
...
mixer = snd_es1688_new_mixer( pcm );
if ( !mixer ) {
snd_pcm_free( pcm );
snd_card_free( card );
return -NXIO;
}
...
if ( snd_mixer_register( mixer, 0 ) ) {
... unregister already registered devices ...
snd_mixer_free( mixer );
snd_pcm_free( pcm );
snd_card_free( card );
return -ENXIO;
}
...
snd_mixer_unregister( mixer );
</PRE>
<HR>
</CODE></BLOCKQUOTE>
</P>
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