(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@gmail.com 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=sharin...
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