USB keyboard LED lights cause audio to stutter

Dominic Marks dom at
Wed Sep 27 02:51:36 PDT 2006


Has anyone else noticed this? Here is how to repeat it:

1. USB Keyboard
2. Sound card (CMedia 8738 in my case)
3. Recent -STABLE

 > uname -v
FreeBSD 6.2-PRERELEASE #10: Mon Sep 18 15:46:33 BST 2006

Now, play some music (I'm using XMMS) and press on any keyboard
key which toggles an LED once a second is enough, just press it often
you will observe that the audio slows down immediately and will slow
down more the quicker you hammer on NUM-LOCK, CAPS-LOCK etc.
Once you stop pressing the key the audio will resume the correct 
All other activities on the system seem to be unaffected by it.

Other keys do not have the same impact. I'm pretty sure this only 
happening recently but I could have just not noticed it as much.

 From watching `systat -vmstat 1` during this it seems that whenever
an LED key is pressed atkb receives between 20 and 100 interrupts and
the slow down occurs.

I'll catch up to -STABLE soon to check if it is still happening.



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