On Mon, 2005-03-28 at 09:42 +1000, Benjamin Herrenschmidt wrote:
> It seems that Apple's driver has an in-kernel framework for doing volume
> control, mixing, and other horrors right in the kernel, in temporary
> buffers, just before they get DMA'ed (gack !)
>
> I want to avoid something like that. How "friendly" would Alsa be to
> drivers that don't have any HW volume control capability ? Does typical
> userland libraries provide software processing volume control ? Do you
> suggest I just don't do any control ? Or should I implement a double
> buffer scheme with software gain as well in the kernel driver ?
alsa-lib handles both mixing (dmix plugin) and volume control (softvol
plugin) in software for codecs like this that don't do it in hardware.
Since Windows does mixing and volume control in the kernel (ugh) it's
increasingly common to find devices that cannot do these. You don't
need to handle it in the driver at all.
dmix has been around for a while but softvol plugin is very new, you
will need ALSA CVS or the upcoming 1.0.9 release.
Lee
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