[alsa-devel] Problem adding support for digital mixer in codec

Peter Ujfalusi peter.ujfalusi at nokia.com
Thu Mar 25 08:17:59 CET 2010


On Thursday 25 March 2010 04:33:54 ext Candelaria Villarreal, Jorge wrote:
> Hi,
> I am trying to add support for a digital mixer. The digital mixer is
> connected like the following example:
> Path 1 -------\
> Path 2 --------\
>                    MIXER ------> DAC----> ...
> Path 3 --------/
> Path 4 -------/
> However, I think ALSA does not support this configuration, as the DAC
> should be the first element in a route. I tried adding the DAC to the
> route first, and connected its output to the mixer inputs, like this:
> 	  {"Mixer", "Multimedia Ext Switch", "HSDAC Left"},
>         {"Mixer", "Multimedia Ext Switch", "HSDAC Right"},
>         {"Mixer", "Voice Switch", "HSDAC Left"},
>         {"Mixer", "Voice Switch", "HSDAC Right"},
>         {"Mixer", "Multimedia Uplink Switch", "HSDAC Left"},
>         {"Mixer", "Multimedia Uplink Switch", "HSDAC Right"},
>         {"Mixer", "Multimedia Switch", "HSDAC Left"},
>         {"Mixer", "Multimedia Switch", "HSDAC Right"},
> But this does not seem to work. Can anyone give me some tips? Any comment
> would be appreciated.

Hmm, how these paths are connected, and where?
What I mean is I suppose you have one path, which is connected to the main CPU, 
than I suspect you have a connection to a modem (voice?), than you have 
possibility to connect some other components via digital link?

What I did with the TWL4030 codec, is that I have moved the actual DAC power 
control from the DAPM_DAC to different widget (the DAPM_DAC is kind of a fake 
one). This was needed to support the digital loopback functionality.

So if you reorder the DAPM widgets (making sure that the switch order still OK), 
than I think you can treat one of the paths as normal playback path (fake 
DAPM_DAC -> mixer (have the DAC power bit handled here) -> ...).
Than you might consider of adding the rest of the paths as DAPM_INPUT, and 
connect them to the mixer (which after the fake DAC).
So you kind of have digital loopback from those to the analog domain.

> Thanks,
> Jorge


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