[alsa-devel] [PATCH]: No sound when using software based mmap support and dmix plugin

[Yogesh Soni]

Hi Takashi,

Thanks for your reply. Please consider the following snippet from
pcm-indirect.h.  When using other plugins (like softvol), appl_ptr was
updated correctly and below code worked well. In case of dmix, The samples
are never copied to substream because
   appl_ptr = rec->appl_ptr = diff = 0  --> rec->sw_ready = 0 .

*snd_pcm_sframes_t diff = appl_ptr - rec->appl_ptr;*
.....
if (*diff*) {
.......
rec->sw_ready += (int)frames_to_bytes(runtime, diff);
.......
}
 while (rec->hw_ready < qsize &&* rec->sw_ready > 0*) {
 *copy(substream, rec, bytes);*
         }

Regards
Yogesh

On Tue, May 19, 2015 at 4:47 AM, Takashi Iwai <tiwai at suse.de> wrote:

> At Wed, 13 May 2015 17:12:33 -0700,
> Yogesh Soni wrote:
> >
> > 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. patch is attached.
>
> Thanks for reporting and the patch.
>
> So, what actually prevents working with the current code in the free
> wheeling mode?
>
>
> Takashi
>