On Wed, 16 Jan 2008, Takashi Iwai wrote:
> At Wed, 16 Jan 2008 15:23:37 +0100 (CET),
> Jaroslav Kysela wrote:
> >
> > Hi,
> >
> > I am actually thinking to add TLV support to each PCM stream. The
> > reason is to obtain various "static" information from the driver without
> > even opening the PCM stream. The current API lack:
> >
> > a) get channel info / name / position (e.g. Front Left Speaker)
> > - not sure how to handle multichannel cards
>
> This won't work with the static TLV because the channel mapping is a
> dynamic information. It varies depending on the hw_params setting.
> A typical difference is the mappings between 4 and 6 channels
> (FL/FR/RL/RR and FL/FR/C/LFE/RL/RR).
>
> > - I'm sure that this is something to be user configurable
>
> Everything is user-configurable :)
>
> But the channel mapping is basically bound to the driver
> implementation, so rather there is no real user-configuration, AFAIK.
>
> I've already hacked to extend channel_info to include this
> information. If you're interested, I'll post patches.
>
> > b) get possible channels
> > c) get possible formats
>
> These *could* be dynamic, too. That's why we have a complex hw_params
> procedure. But, they are static for most cases, so it would likely
> work.
Ok, I didn't explain the term "static" as well. I think that the best way
might be to group parameters like:
parameters #1 {
channels {
2 { FL, FR }
4 { FL, FR, RL, RR }
6 { FL, FR, C, LFE, RL, RR }
}
formats {
S16_LE, S32_LE
}
}
parameters #2 {
....
}
Just idea. We can get this change as base to change from refine method to
provide a list of possible values method and reduce the kernel and
alsa-lib code.
> > d) various inter-PCM-device constraint description (e.g. if S/PDIF
> > PCM stream can be used with analog etc.)
>
> This sounds good. Any practical use in mind?
I think that Lennart Poettering requirested this and I think that it might
make sense for various TV Linux boxes ;-)
Jaroslav
-----
Jaroslav Kysela <perex@xxxxxxxx>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.
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