[ntp:hackers] Strange Dell

David L. Mills mills at udel.edu
Tue Oct 24 20:09:50 PDT 2006


Guys,

A Dell Optiplex 280 fell from the sky to land on my lap. I intend to use 
this machine to watch miscellaneous exotic audio signals (WWV, etc), 
since it has a small footprint and can fit in odd corners of my home 
office/machine room. I found very strange behavior with FreeBSD 6.1. 
Once each minute a 120-ms slip occurs in the audio codec samples. Each 
slip loses 960 (more or less) from the sample stream. The slips have not 
occured in any other machine running Solaris or FreeBSD.

A 120-ms slip once a minute does not seem likely due to ACPI, but to be 
sure I turned ACPI off. It doesn't seem likely due to lost interrupts, 
as something would have to disable interrupts for 960 codec samples. The 
codec buffer size is 180 samples or 22.5 ms, so lost packets don't seem 
credible. Just to make sure I used the Unix netstat -m to watch for mbuf 
leaks and there were none. The WWV driver code is identical to that 
runing fine in other FreeBSD boxes with the same operating system and 
configuration.

I configured the machine to use the resident CDMA server and ran it for 
a couple of days with no problem. Whatever is happening seems to affect 
only the audio codec, which is almost certainly AC97 compliant. Any ideas?

Dave




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