BeagleBone Black Audio Cape Buffer Overruns

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1

I'm currently struggling with the BeagleBone Audio cape on a BeagleBone black. I keep getting ALSA buffer xruns when capturing audio. Has anyone successfully done any recording using the audio cape and if so how did they do it?

I am currently running 3.13-rc7 mainline and I was experiencing the same behaviour on 3.8. Recording to a uSD card is worst, then eMMC and I have even seen buffer overruns when recording directly to tmpfs once or twice. I am worried that it may be a problem with the audio driver, or something is blocking interrupts for too long and the interrupt to empty the ALSA buffer is being missed.

Does anyone have any input?

Cheers,

2

The best “temporary solution” that worked for me was using SoX for recording audio (instead of the “arecord” command). I get just a few buffer overruns, once in a while…
But, definitely, this is not a solution. It would be nice if someone could clarify this issue.

Regards,

Ezequiel

3

Thanks Ezequiel, I'm currently chasing this down at a kernel driver level so will update if I manage to get anywhere. Good (?) to hear that I'm not the only one with problems.

4

I managed to fix my issues by hacking the buffer size of the driver in
the kernel. There is something still not quite right with the
implementation as the max_buffer_bytes seems to be calculated wrong
somewhere, but I can't seem to find where.

So, if you are interested in helping fix your buffer xrun problems I
would suggest changing the buffer_bytes_max value of the
snd_pcm_hardware capture struct in sound/soc/davinci/davinci-pcm.c,
256*1024 will give you 64K of buffer, rather than the current 32K.

Cheers,

5

I think the dma transfers that are happening due to writing to the uSD/eMMC are causing high latency in the IRQ's, which therefore stops data being pulled out of the buffer and as such overrunning.

I think there are a couple of factors to it in all honesty and this is just a quick fix, but to really fix it I think whatever IRQ is hogging the scheduler needs to be fixed.

I mentioned in my email the file that I was hacking in order to increase the buffer:

sound/soc/davinci/davinci-pcm.c

Which is part of the kernel. I am using 3.13, but i expect it will apply to 3.8 or whatever you are running too.

Cheers,