Michael, thanks for that excellent explaination.  I agree that a periodic
timer would be helpful .. especially with respects to the 3COM.  However,
I was able to recreate the "stopped logging" scenario within minutes of
booting .. So that wouldn't help with what was happening with the AHC.

I think for my situation, the short term solution is to just use a 
different card. 

> think that has been fixed in -current and 1.6).  I've been able to clear
> this condition by getting into the debugger and calling the routine to
> enable the interrupt (I can't remember the exact procedure at the moment).

Since it was occuring within seconds of running my for i in sd1a sd2a ...
it wouldn't help :(

Thanks again.