[alsa-devel] External plugin question

[Takashi Iwai]

On Fri, 07 Aug 2015 02:02:47 +0200,
Mina Almasry wrote:
> 
> I'm new to alsa dev and I'm trying to write a very simple external pcm
> plugin. I want my pcm plugin to output sound to multiple slave pcms when
> sound is being writei'd to it. So:
> 
> snd_pcm_myplugin_writei(pcm, buffer, size) {
>   foreach slave pcm {
>     snd_pcm_writei(slave_pcm, buffer, size);
>   }
> }

Can't it be better managed by splitting to multiple plugins, e.g.

   filter -> multi -> slave PCMs

??

> I'm having trouble implementing this plugin because the external plugin sdk
> does not allow me to define the writei function for my plugin, but lets me
> define the transfer function which has a very different signature than
> writei:
> 
> transfer(snd_pcm_ioplug_t *io, const snd_pcm_channel_area_t *areas,
> snd_pcm_uframes_t offset, snd_pcm_uframes_t size)
> 
> how do I extract buffer and size from these arguments? Any tips on how I
> write my plugin.

This is a kind of abstracted form to handle both interleaved and
non-interleaved formats.  The areas argument is the array of buffer
pointers.  Each of the array member corresponds to the buffer and the
step of each channel.  The rest, offset and size, are trivial and
same.


Takashi