querying card properties

querying card properties

[Lee Revell]

In a recent LAU thread it came to light that some (all?) distros alsa
setup scripts don't configure dmix when the card is known not to support
hardware mixing.  The end result is the user has to edit config files to
get software mixing to work.  On a modern distro this is a BUG.

Is there an API function to detect whether hardware mixing is supported?
Also useful would be a way to detect codecs with no hardware volume
control, so the softvol plugin can be set up.

I know there are hacks like comparing the number of streams to the
number of substreams, but what's the right way?

Lee






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Re: querying card properties

[Takashi Iwai]

At Sat, 08 Jan 2005 16:52:24 -0500,
Lee Revell wrote:
> 
> In a recent LAU thread it came to light that some (all?) distros alsa
> setup scripts don't configure dmix when the card is known not to support
> hardware mixing.  The end result is the user has to edit config files to
> get software mixing to work.  On a modern distro this is a BUG.
> 
> Is there an API function to detect whether hardware mixing is supported?

No specific API for such probes.

> Also useful would be a way to detect codecs with no hardware volume
> control, so the softvol plugin can be set up.

This is already implemented on 1.0.8rc2.  The "default" PCM is
overwritten automagicall on some cards like ICH, NFORCE, or VIA.
On such cards, the default PCM always routes via softvol plugin.  The
softvol plugin checks whether the specified control is a hardcoded
one.  If it's a h/w control, the plugin just bypasses.  No performance
drawback.  OTOH, if it's a user-defined one, it applys the software
volume attenuation.

So, we can simply add dmix to the definition of card's specific
default PCM.  Take a look at alsa-lib/src/conf/cards/ICH.conf, for
example.  I didn't do that at this time simply because dmix has
still a bit problems, which I'm currently trying to debug/improve...


> I know there are hacks like comparing the number of streams to the
> number of substreams, but what's the right way?

Yes, I think it's a way to check from an application.


Takashi


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