[alsa-devel] Issue with Dmix
abdulmateen.shaikh at gmail.com
Mon Mar 4 11:25:06 CET 2013
Can anybody please guide us in this situation.
On Mon, Feb 25, 2013 at 11:38 AM, mateen <abdulmateen.shaikh at gmail.com>wrote:
> We have enabled DMIX plugin for sample rate conversion and mixing of 2 pcm
> streams in our alsa package (Alsa lib 1.0.22 and alsa driver 220.127.116.11) to
> 48K output Sample rate.However we are seeing a noise issue with 44100
> Sample rate input streams or Unsigned Stereo 48K stream.
> This is how our current design is:
> We call snd_pcm_lib_malloc_page() in which alsa driver internally
> allocates a dma buffer and map it when Dmix is invoked.
> We currently reads from that mmaped buffer to our hardware buffer inside a
> transfer_ack_begin() function which is called from snd_pcm_period_elapsed().
> However we are getting a problem in understanding how do we know how much
> data has been written by dmix lib in mapped buffer? As we see no ioctl or
> corresponding hardware function call where dmix may pass information on
> Size of data being written to our driver.
> We do see appl_ptr and hw_ptr in runtime->mmap->control and status struct.
> Out architecture doesn’t support defining and mapping of these status and
> control structure at hardware level.Thus Dmix lib allocates them and copy
> them to runtime substream via ioctl. As far as I could understand both
> appl_ptr and hw_ptr are initialised to 0 and then appl_ptr is the one
> adjusted by lib after every write. Should we tap this value to update
> hw_ptr value in status information? Will difference of hw_ptr and appl_ptr
> will let us know amount of frames been written?
> Can anyone please help us to understand criteria and concept of data copy
> from intermediate to hardware buffer?
> Any information on this would be of immense help.
> Shaikh Mateen
Shaikh Mateen S.
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