[alsa-devel] Software based mmap support and dmix

[Yogesh Soni]

Hi all,

I am trying to have dmix plugin work ( I succeeded) with the audio card
that does not have hardware mmap support and uses pcm_indirect method to
map software buffer for mmap feature.

Most of the plugins were working quite well with mmap/pcm_indirect combo.
However, dmix plugin did not work (no sound). I debugged and realized that
appl_ptr in pcm_direct.h(snd_pcm_indirect_playback_transfer()) was always 0
and hence nothing got copied to slave pcm buffer. I then discovered that
dmix operates in freewheeling-mode..

I have made a small workaround patch (I believe it can be cleaned up) in
case of free-wheeling mode, basically using sw_ready to hold bytes that
need to be copied. I used rec->sw_ready because it looked safest to use for
this purpose. As a result of this patch, normally period_size bytes are
copied to pcm buffer every period and sound is playing smooth.

I am a noob in alsa and linux in general. So, I would like your opinion on
the patch. I would much prefer if I could write a patch that is generic and
clean enough, so that it could be used by others. New pcm-indirect.h
attached.

Thanks a lot for your help.
Regards
Yogesh
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