Thanks Takashi, I tried your directions.

The outcome was the following:
dxs_support=2 caused no audio output at all (though there were no visible 
errors; I guess there's some issue with the hw mixer)
dxs_support=3 works, but then I cannot play on device 0 because 44.1kHz 
audio produces a nasty click on every fragment; I think that must be a bug 
in the sample rate convertor

Setting the output plugins manually gives these results:
dmix on device 1 (single channel) produces stutter on every period, changing 
the period time only makes it stutter faster or slower
rate conversion on device 0 (multi channel) results in the same clicks as 
when using dxs_support=3

Performance is absolutely no issue here, my machine is an Athlon XP 2100+.

As you pointed out, the problem probably lies in the BIOS. I'll try to 
update that and tell you the results (will be a little difficult, I don't 
have a floppy drive).

Anyway, here's my chip info:
00:11.5 Class 0401: 1106:3059 (rev 50)
        Subsystem: 1043:8095
        Flags: medium devsel, IRQ 9
        I/O ports at e000 [size=256]
        Capabilities: [c0] Power Management version 2

On Wednesday 02 July 2003 18:50, Takashi Iwai wrote:
> unfortuantely, some motherboards have the problems of DXS channels.
> on some, DXS mode doesn't work at all, and on some, only 48kHz is
> available (otherwise you'll hear click noises).
> according to the people of VIA tech, this is because of the BIOS
> (typically AWARD BIOS).  so, one solution is to update the BIOS.
> but it's not always a preferred solution.
>
> in the recent driver version, a workaround is provided instead.
> there is a module option "dxs_support", which defines how to handle
> the DXS channels.  if you have a problem with the first pcm device,
> try dxs_support=2 or dxs_support=3.
>
> when dxs_support=2 is given, the DXS mode is disabled and you'll have
> only the multi-channel playback mode.  this means, the chip is handled
> as VIA8233A.  of course, you can play only on stream.  in this case,
> dmix plugin would be a workaround.
>
> when dxs_support=3 is given, only 48kHz is allowed for the DXS
> channels.  that means, the sample-rate conversion will be done in
> alsa-lib or OSS-emulation for playing MP3.  but it's cheaper than dmix
> plugin.  so, try this once, and if still doesn't work, try the
> previous one.
>
> how to add such an option?  if you already have module options for
> via82xx driver, you should see the line like following in
> /etc/modules.conf
>
>       options snd-via82xx index=0
>
> and just add dxs_support=2 (or 3) there.
>
>       options snd-via82xx index=0 dxs_support=2
>
> then restart the driver.
>
>
> in future, i'll add a black-list of motherboards which don't work well
> with DXS mode.  if your mobo needs the workaround above, please let me
> know the pci-subsystem vendor/device ids, which can be obtained via
> "lspci -nv" command.
>
>
> Takashi



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