This is our proprietary mobo. In case you want a quick glance, http://www.nexcom.com/product/nex/nex7220/
North Bridge: E7501 South Bridge: ICH3 - S SuperIO: SMSC(LPC47B27x) I base on the code for tyan/s2735.
If it was the serial interrupt, why didn't it happen earlier? It starts getting slow at certain point in the linux kernel.
gin