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
-----
hw_ptr : 26942906
appl_ptr : 26942906
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).
This didn't happen with earlier versions of alsa using the same playing software.
I hope this helps the developers in tracking down any bugs.
Thanks, - Steve
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