Re: External PCM plugin SDK

[Takashi Iwai <tiwai@suse.de>]

At Wed, 09 Feb 2005 18:27:16 +0100,
Marcel Holtmann wrote:
> 
> Hi Takashi,
> 
> > > it is putting the PCM data into the SBC encoder and then sending it to
> > > the RFCOMM socket. This is not the standard for high quality audio over
> > > Bluetooth, but my Aiptek headphone supports this stuff. For now this is
> > > easier than dealing with A2DP and AVDTP.
> > > 
> > > The SCO support for the headsets is another story.
> > 
> > ... and we'll need control plugin for mixers, too.
> 
> and I need full duplex IO and volume control inside the same plugin for
> the headset/handsfree support.

Hmm, the share of volume control stuff between PCM and control plugins
might be a bit tough.

> > > The XMMS is version 1.2.10 and BMP is version 0.9.7. In what versions
> > > are the ALSA plugins fixed. I will build it from source.
> > 
> > The patch isn't in the released version.  IIRC, they were applied to
> > CVS, though.
> 
> I checked the latest XMMS CVS and even it segfaults or I get an error:
> 
> xmms: pcm_params.c:2294: sndrv_pcm_hw_params: Assertion `err >= 0' failed.
> 
> Looks like a problem on my side.
> 
> > > > Do you have buffer or period size constraints?
> > > 
> > > Oh yes, that is the point where I am not sure what I am doing. The SBC
> > > is a codec like MP3 and actually I have no idea what are the best values
> > > here. These are software soundcards.
> > 
> > You don't have to set them if the hardware has no restriction.
> > Usually, the period size defines the interrupt period.  In the case of
> > user-space driver, it corresponds to the expected poll period, etc.
> 
> I can skip IOPLUG_HW_PERIOD_BYTES and IOPLUG_HW_PERIODS, but I must set
> IOPLUG_HW_BUFFER_BYTES, because otherwise it segfaults even with aplay.

OK, then use snd_pcm_ioplug_set_param_minmax() with some sane values.

> > > > > We also talked about making these IO plugins visible when ALSA is
> > > > > listing its hardware devices. Is this possible now?
> > > > 
> > > > No, it's still in planning.
> > > > We'll need to define a usable API first...
> > > 
> > > What about a flags variable in snd_pcm_ioplug for activating it. This is
> > > generic and for me this is enough, because both Bluetooth IO plugins are
> > > virtual soundcards and they should always be listed. Or maybe list IO
> > > plugins in general.
> > 
> > This sounds good.  I'll add like the following:
> 
> Let's take an unsigned long to handle more than 32 flags ;)

Well, I'd like to keep 32bit.

Nowadays no one knows whether the exported struct is shared between
32bit and 64bit environment.  Once if we have to implement a 32bit
wrapper, the difference of long is simply a pain.


Takashi


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