Re: Number of sound channels?

Jeff Garzik (jgarzik@mandrakesoft.com)
Thu, 09 Dec 1999 15:38:55 -0500

Thomas Sailer wrote:
>
> Alan Cox wrote:
> >
> > > The Via audio chip has a single read channel and a single write
> > > channel. Do I treat this as a single channel with read and write
> > > capability, or two separate channels?
> >
> > Single full duplex I think
>
> Mostly I do it both ways - if /dev/dsp is opened O_RDONLY (or O_WRONLY),
> another process is allowed to open it O_WRONLY (or O_RDONLY). If it
> opens O_RDWR, noone else is allowed.

This is how I implemented via_dsp_open as well.

Is this why USB's audio device handling of SNDCTL_DSP_SETDUPLEX is null?

case SNDCTL_DSP_SETDUPLEX:
return 0;

> This is sometimes useful, Sun does it also that way (but it only
> works if you can set the sampling rate independently for both
> directions).

Or you have cheap hardware with a fixed sample rate which is the same
for both channels. :) AC97 1.0-compliancy requires at least that.

-- 
Jeff Garzik              | Just once, I wish we would encounter
Building 1024            | an alien menace that wasn't immune to
MandrakeSoft, Inc.       | bullets.   -- The Brigadier, "Dr. Who"


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