Re: negative timestamps on pcm?!?

[Takashi Iwai <tiwai@suse.de>]

At Mon, 20 Oct 2003 11:05:29 -0700,
Steve deRosier wrote:
> 
> All,
> 
> We've noticed a problem with the newest version of Alsa while doing some 
> stress testing of our devices.  Basically, the scenerio is we're playing 
> through a large library of .ogg files over the weekend.  When we checked 
> on the progress upon getting in on Monday, we discovered that the PCM 
> had ceased playing, and our ogg player had started a ton of instances 
> (one for each song it was supposed to play) and couldn't play on any of 
> them.  Looking at /proc/asound/card0/pcm0p/sub0/status:
> # cat status
> state: OPEN
> trigger_time: 642.000000000
> tstamp      : -1071072720.-1071072332
> delay       : 498
> avail       : -1072507698
> avail_max   : -1071072720

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


> -----
> 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.


> 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.

which version of ALSA driver are you using?


Takashi


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