Subject: audio channel support
To: None <>
From: Reinoud Zandijk <>
List: tech-kern
Date: 01/06/2005 02:06:28
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Dear folks,

when trying to test my new auixp(4) driver (commit pending) i've stumbled 
against linux code that uses the SNDCTL_DSP_GETCHANNELMASK ioctl call that 
is not part of the official OSS standard. The result of the 
SNDCTL_DSP_GETCHANNELMASK ioctl is a value that has bits set for each 
speaker that is available so programs can determine what audio support 
there is.

In trying to fix this piece of code (in vlc... not yet dared to touch the 
compat code ;) ) i've noted that NetBSD doesn't support querying or setting 
speaker preferences. I.e. i can't setup my system for quadrophonic audio or 
for dolby 5.1 by default.

Since auixp(4) can support mono, stereo, quadraphonic or dolby 5.1 (and 
SPDIF... only not implemented yet) wouldn't it be more `sane' to have the 
userland setup my stereoset settings (say quadraphonic) and let the kernel 
report it doesn't have dolby 5.1 available since - although the chipset 
supports 5.1 i `only' have quadrophonic audio available?

Next to that, would implementing the missing linux ioctl call be a good 
idea? That would give allmost all linux programs that do support more than 
stereo automatic access to dolby 5.1 audio since most programs i've seen 
seem to rely on this call being present if more than stereo is requested.


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