Re: Stream Synchronization of VXPocket 440 card

[Takashi Iwai <tiwai@suse.de>]

At Thu, 7 Oct 2004 13:44:04 -0700 (PDT),
Hanbiao Wang wrote:
> 
> Hi all,
>     VXPocket 440 card has two stereo input streams. Can these two streams be
> synchronized by calling snd_pcm_link()?
>     According to the ALSA project webpage, streams can synched only if the
> hardware supports this feature. The ALSA project webpage, the
> snd_pcm_info_get_sync() function returns synchronization ID -
> snd_pcm_sync_id_t, which is equal for hardware synchronized streams.
> I examined the sync IDs of these two streams of the VXPocket 440 card as
> follows:
> 1. call snd_pcm_open() on hw:0,0 in order to get pcm handle h0
> 2. call snd_pcm_info() on pcm handle h0 to get pcm info f0
> 3. call snd_pcm_info_get_sync() on f0 to get sync ID0 of hw:0,0
> 
> 4. call snd_pcm_open() on hw:0,1 in order to get pcm handle h1
> 5. call snd_pcm_info() on pcm handle h1 to get pcm info f1
> 3. call snd_pcm_info_get_sync() on f1 to get sync ID1 of hw:0,1
> 
> snd_pcm_sync_id_t has three data fields:
> unsigned char 	id [16]
> unsigned short 	id16 [8]
> unsigned int 	id32 [4]
> 
>     ID0.id is "-1073743584" while ID1.id is "-1073743600". These sync IDs
> are apparently not identical. So these two streams look like not synched
> by the hardware. However, the manufacture of VXPocket 440 cards told me
> that these two input streams share the same internal hardware clock. So
> there is no obvious reason for the hardware not to synchronizes these two
> input streams. The is a contradiction to me. Is there anything wrong in my
> examination code? Please help me on this issue if you have any experience
> related to my question. Thanks a lot in advance.

You're not wrong.  The h/w sync feature is not implemented (yet) on
ALSA vx drivers :)  You can still use software sync with
snd_pcm_link(), though.


Takashi


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