Re: External PCM plugin SDK

[Takashi Iwai <tiwai@suse.de>]

At Wed, 09 Feb 2005 15:37:49 +0100,
Marcel Holtmann wrote:
> 
> Hi Takashi,
> 
> > > > I now commited a patch to add the external PCM plugin SDK to
> > > > alsa-lib.  This allows you to create ALSA PCM plugin outside the
> > > > alsa-lib tree.  It's still a draft version, and currently only the I/O
> > > > plugin (e.g. for implementation of user-space driver) is provided.
> > > > The filter-type plugin SDK (e.g. for effects) and the control plugin
> > > > SDK will follow later.
> > > > 
> > > > No documentation yet.  Look at the code :)
> > > > 
> > > > Example I/O plugins are found in alsa-plugins tree.  So far, two
> > > > plugins, OSS and JACK plugins.  The former one is the plugin to
> > > > emulate ALSA API with the OSS driver.  The latter is almost identical
> > > > with the one in alsa-lib/src/pcm/ext.
> > > > 
> > > > I think this SDK can be used for better implementaion of BT-SCO and
> > > > FireWire.
> > > 
> > > I wrote a quick and dirty prototype using SBC over RFCOMM for now.
> > 
> > Wow.
> 
> 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.

> > >  It is
> > > working with aplay and the alsaplayer, but not with xmms or beep. Are
> > > there any known problem with these ALSA plugins?
> > 
> > Which xmms/bmp are you using?
> > I fixed ALSA plugins of xmms and bmp recently, so it might have been
> > fixed.  For testing, you can try the one in SUSE's rpms from STABLE.
> 
> 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.

> > 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.

> > > 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:

Index: alsa-lib/include/pcm_ioplug.h
===================================================================
RCS file: /suse/tiwai/cvs/alsa/alsa-lib/include/pcm_ioplug.h,v
retrieving revision 1.3
diff -u -r1.3 pcm_ioplug.h
--- alsa-lib/include/pcm_ioplug.h	8 Feb 2005 20:48:56 -0000	1.3
+++ alsa-lib/include/pcm_ioplug.h	9 Feb 2005 15:14:06 -0000
@@ -37,10 +37,13 @@
 typedef struct snd_pcm_ioplug snd_pcm_ioplug_t;
 typedef struct snd_pcm_ioplug_callback snd_pcm_ioplug_callback_t;
 
+#define SND_PCM_IOPLUG_FLAG_LISTED	(1<<0)
+
 /* exported pcm data */
 struct snd_pcm_ioplug {
 	/* must be filled before calling snd_pcm_ioplug_create() */
 	const char *name;
+	unsigned int flags;	/* SND_PCM_IOPLUG_FLAG_XXX */
 	int poll_fd;
 	unsigned int poll_events;
 	unsigned int mmap_rw;		/* pseudo mmap */



Takashi


-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click