(Ping) I'm afraid I still don't understand why this is failing. I found that a call to sdn_pcm_wait() when -EAGAIN is returned fixes the problem because it waits for samples to be ready, but I don't understand why it is a problem in the first place. Much of the sample code is written in a way that suggests that the call to snd_pcm_wait() is optional, and only required when directly reading/writing from the device (MMAP, I'm not doing this). I'm just wondering what is wrong with basically looping over a call to snd_pcm_readi() in non-blocking mode, reacting to errors, and capturing frames. This produces awful static (which is basically garbage samples), is it a requirement that I call snd_pcm_wait() when -EAGAIN is passed back to wait for a full period to be ready? Thanks, - Trent Reed On Tue, Jun 28, 2016 at 7:27 PM, Trent Reed <treed0803@xxxxxxxxx> wrote: > Hey All, > > I've been banging my head against the wall for about a week on this bug. > The following gist shows my sample reproduction code: > https://gist.github.com/TReed0803/985c5d5c3d295245e19006a27be447c3 > > I'm simply opening up a non-blocking PCM capture stream and writing the > contents of the reads to stdout. > (Originally, I was writing to the playback stream, but I was hearing this > strange static occasionally!) > > It's the static I'm trying to debug. It doesn't happen every time. In > fact, sometimes I'll go a few consecutive executions without hearing it. > I was able to capture some of the bad data, and I loaded it up in Audacity > for visualization: > > https://drive.google.com/file/d/0B-1aumGKQcQTcUJoZzIwRWhYSFE/view?usp=sharing > > It looks like the internal buffer occasionally is sending me more data > than it actually captured, and I end up either reading old PCM data from > the internal ring buffer, or (at the very beginning) a bunch of zeros. > > Can anyone help me understand what is going on? What could cause these > definitely incorrect samples to be recorded? (I get the same effect > regardless of hardware, but I will list hardware just in case.) > > I hope I have all the information you might need: > Hardware: Samson Meteor Mic (USB-Audio, USB Mixer) [Though, it even > happens with my built-in microphone] > ALSA version: Advanced Linux Sound Architecture Driver Version > k4.4.0-28-generic. > apt-cache policy (installed alsa-lib version): 1.1.0-0ubuntu1 > > Thanks, > - Trent Reed > _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
