Re: alsa-lib mixer-interface: snd_mixer_selem_get_capture_switch()

[Takashi Iwai <tiwai@suse.de>]

At Sun, 23 Nov 2003 20:23:11 +0100,
Christian Esken wrote:
> 
> Hello,
> 
> I have problems with snd_mixer_selem_get_capture_switch(elem,pos,&value)
> in my KMix mixer application. The "value" returned does *not* reflect the 
> actual state in all cases.
> Probably I am doing something wrong, if somebody could throw me a hint I would 
> be more than happy. I have investigated for days and feel completely lost.
> 
> It is a bit complicated, so I'll do a step-by-step walkthrough of an example:
> 
> 1) Initially switch "1" is ON and switch "2" is OFF
> 2) I enable switch "2". 
> 3) The ALSA driver detects that switches "1" and "2" cannot be ON at
>   the same time. So the ALSA driver disables "1".
> 4a) KMix now shows switches "1" and "2" both as ON, because
>   snd_mixer_selem_get_capture_switch() reports them as ON.
> 4b) alsamixer shows switch "1" is OFF and switch "2" is ON.
> 
> So I wonder why snd_mixer_selem_get_capture_switch() works in alsamixer and 
> not in KMix.
> The only differenece I see is that alsamixer has these poll-descriptor stuff 
> in it. Do I possibly need to implement it (I don't understand what I would 
> have to do there - it looks complicated)?

yes, otherwise the update won't occur.
in the case of qt, you can do polling via connecting QSocketNotifier.

>  Or is there some other means to 
> "update" the state of the mixer elements?

it's not so easy, since you'll need to receive the information which
element should be updated at each time when a change occurs.
otherwise you'll have to update all elements at once.


Takashi


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