Re: alsa timestamps

[Heikki Lindholm <holindho@cs.helsinki.fi>]

Takashi Iwai kirjoitti:
> At Mon, 19 Nov 2007 15:41:46 +0200,
> Heikki Lindholm wrote:
>> Jaroslav Kysela kirjoitti:
>>> On Mon, 19 Nov 2007, Heikki Lindholm wrote:
>>>
>>>> Heikki Lindholm kirjoitti:
>>>>> Hello list,
>>>>>
>>>>> I took up some old dusty code of mine that uses snd_pcm_state followed 
>>>>> by snd_pcm_status_get_tstamp when in capture mode. The code used to 
>>>>> work, but now the returned timestamps are all zeroes. Is there some API 
>>>>> change done recently or is the whole timestamping deprecated or 
>>>>> something? I've tried with different drivers on ubuntu's alsa .14 and 
>>>>> gentoo's .14. I've also tried mmap'ed and r/w modes, and I'm setting the 
>>>>> TSTAMP_MMAP sw param.
>>>> I figured out that this doesn't happen when using hw:x,y devices. Is it 
>>>> a documented feature that some (software?) devices don't fill in timestamps?
>>> I think that it should be fixed. Could you send us 'snd_pcm_dump()' for a 
>>> non-working device? It's probably ommited code in direct pcm plugins (dmix 
>>> & etc.).
>> Here goes. The driver is snd_aoa. It seems as if the timestamp mode 
>> isn't propagated to the hw device.
> 
> AFAIK, the time-stamp mode isn't handled properly with direct plugins
> because of its nature.  Since the direct plugins share the same PCM
> hardware instance with multiple processes, you cannot change the
> parameter arbitrarily from a single client.
> 
> We may implement an emulation in alsa-lib instead, though...

For the time being, is there any other way of determining whether a pcm 
supports time stamps than just trying out and seeing if zero is all that 
comes out?

-- Heikki Lindholm