[alsa-devel] oss emul: powerbook5,3 microphone to mono

[Lee Revell]

On Thu, Apr 9, 2009 at 5:34 PM, Robert T. Drury <rtdrury at earthlink.net> wrote:
> On machine powerbook5,3 the built-in microphone is attached to
> the right channel of the sound chip.  In the alsa oss emulation
> in linux-2.6.23.9 (alsa-*-1.0.12) the plugin layer copies the
> left input channel to a one-channel buffer when  calling ioctl
> SNDCTL_DSP_CHANNELS with one channel.  So no mic to mono on the
> powerbook5,3.
>
> In the kernel source: linux-2.6.23.9/sound/core/oss/pcm_plugin.c:
>
> The function snd_pcm_plug_read_transfer copies from the two
> channel hardware input buffer to the one channel user space
> buffer.   The left source channel appears to be selected for
> copy in function snd_pcm_plug_format_plugins.  One approach
> is to query line/mic input there for powerbook5,3 and select
> right channel source for copy.  Any ideas?

Try a recent ALSA.  The latest is 1.0.19.  1.0.12 is way too old to debug.

Lee