Re: negative timestamps on pcm?!?

[Steve deRosier <derosier@pianodisc.com>]

> 
> when the state is OPEN, these values are bogus, since snd_pcm_status()
> returns immediately without putting the values.
> 

So, alsa writes bogus data to the proc entries?  Maybe it shouldn't 
write bad data, just leave the spots blank, initilize with 0's or 
something else?

>>-----
>>hw_ptr      : 26942906
>>appl_ptr    : 26942906
> 
> 
> they are real values.
> 
> 
> i can't remember any reason of the restriction above.
> i think it's ok to remove it.
> 

What restriction is that?

>>It seems that our ogg player is set to blocking behavior and each one is 
>>blocked on the call to open the pcm.  The intrieging thing is the 
>>timestamp is negative.  It jumped out that this just looks wrong!
>>
>>Hypothesis 1:  After a really long time playing, the timestamp on the 
>>pcm wraps to negative.  alsa can't handle this and blocks on the output. 
>>  It's no longer running, but is still in an OPEN state so nothing else 
>>can open it.  alsa should either use an unsigned value so large that it 
>>is impossable to overflow (???), use an unsigned and detect overflow and 
>>handle it gracefully, or use a signed value and detect the overflow/wrap 
>>and handle it.
>>Hypothesis 2:  We're barking up the wrong tree and the only thing wrong 
>>is that the proc entry is formmated poorly.  (but even if that is the 
>>case, the problem still happens where after prolonged time alsa stops us).
> 
> 
> at least, the values above make no sense.

Right, the values make no sense, but I think we've explained that away 
now.  So, what is causing alsa to eventually stop playing right?  Yes, 
that's not exactly a fair question... where should we start looking? 
Maybe a mutex, race condition, or an off-by-one error somewhere?

> 
> which version of ALSA driver are you using?
> 

Driver: 0.9.7c
Library: 0.9.7
(retrieved from the website just a few days ago)

Thanks,
- Steve



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