Re: Alsa handling of spdif bits (was Re: Questions to HDSP users)

[Takashi Iwai <tiwai@suse.de>]

At Fri, 06 Feb 2004 20:12:44 +0100,
Thomas Charbonnel wrote:
> 
> >> so I'm back with my 
> >>question concerning amixer : all the 'value' fields of IEC ctls show a 
> >>question mark. Is this a problem with the driver ? If not what would be 
> >>the syntax to access those ctls ?
> > 
> > 
> > amixer doesn't handle IEC958 status properly.
> > 
> > 
> 
> IIUC, this ctl is supposed to be used for example by DVD playing 
> applications so that the fact they may temporary require the Non-Audio 
> bit to be set for AC3 passthru does not interfere with the user settings ?

yes and no.  these bits are set as the parameters of PCM hook plugin.
you can open an spdif PCM with parameters like

	iec958:{AES0=XXX,AES1=XXX,AES2=XXX,AES3=XXX} 

to pass the proper status bits (this will change "IEC958 Plaback PCM
Stream" usually).  xine and mplayer pass these parameters at the open
time.

but my statement above means that amixer doesn't display/parse
correctly this data type (iec958).  it's just a missing feature of
amixer.  it'd be better if amixer handles it correctly.


> If so I'll keep this ctl and implement it properly.
> 
> Anyway thanks for clarifying, it was much needed :)

well, this should be more better documented.
(the patch to the doc is also welcome, BTW ;)


ciao,

Takashi


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