Beagleboard and USB DAC: Sound cracking and CPU load?

[bennerhq]

hello experts,

my beagleborad is spinning and everything is great... well except for one thing that i can't find a solution: when i want to play audio from a USB DAC the audio starts to crack and the CPU maxes out... audio playback via the build in audio is working perfect without maxing out the CPU.

anybody know if there is a solution to this?

thanks in advance,
br/benner

ps: have tried the suggestion from the following two links, but with no luck:
1) https://wiki.archlinux.org/index.php/Ad ... ound_Cards
2) http://alsa.opensrc.org/Usb-audio#Tunin ... _latencies

[pepedog]

I searched this forum for asound
1st hit looks good
viewtopic.php?f=27&t=2057&p=11121&hilit=asound#p11121

[bennerhq]

thanks a trillion!
br/benner

[Daimusou]

It has been observed that doing streaming USB I/O causes an inordinate number of "wakeups" (thousands per second), and each wakeup causes the "kworker" process to do something. kworker is actually part of the kernel, but you can see it in a 'top' display. It is kworker that is using up all the CPU time.

This has been observed with audio and with video to and from USB devices.

My own hypothesis is that this is caused by something at a low level using the minimum DMA buffer size (32 bytes) rather than something larger, but the culprit has not yet been located so this is just a guess at this point. The total amount of memory available to USB DMA operations is 32KB on the chip used in the BeagleBone.