Re: pcm parameters, digital output ...

[Johannes Berg <johannes@sipsolutions.net>]

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On Thu, 2006-03-30 at 16:51 +0200, Jaroslav Kysela wrote:

> The mask is R/O variable and the bit definitions are different for 
> consumer and pro modes, so the driver can describe exactly which bits are 
> supported for these two different modes.

Yes, I know, I just don't see why there are different modes. If the chip
has different modes, shouldn't the driver be able to switch between them
based on the consumer bit in the actual iec958 values it gets from
userspace?

> AC97 code is probably not a good example. The "shift" to specific PCM 
> device is not implemented there. Look to snd_ice1712_spdif_build_controls
> in ice1712.c . This code is good.

Hmm, ok. Did you read my earlier discussion about why I do *not* want a
shift to a specific pcm device?

> I'm not sure, if we need a new format when we have information from the 
> control elements, that the stream is not PCM encoded. But on other hand, 
> these formats can be used with some conversion layers in alsa-lib 
> for handling of these streams and prevent extra things like resampling, 
> volume processing etc.

Aha, good point, I could use the iec958 bits to determine the mode. But
that's out-of-band information, so it is not too nice to rely on it
imho.
And exactly like you say, resampling etc. cannot be done on compressed
information.

> Also, there is a possibility to use subformat value (which is not used 
> so far for S16_LE/BE formats) for the non-pcm stream specification.

I'm not too familiar with these internals :)

What I'm currently doing is defining for each codec what kind of
transfer formats it supports, see 
http://johannes.sipsolutions.net/gitweb.cgi?p=snd-aoa.git;a=blob;h=e3ca7a269906ceb41b411afcad14c54f4a181588;hb=4e1bc0b35020b3b1cac87f60cb67671e2c9a801e;f=aoa/codecs/onyx/snd-aoa-codec-onyx.c#l430

Then the generic framework cuts that down to whatever is usable() at the
moment depending on the selection of the iec958 and analog mute mixer
elements. Hence there you can see what I'd like to do with a new format
(which I called SNDRV_PCM_FMTBIT_COMPRESSED_16BE for now).

johannes

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