I have experimented a bit with an ath@cardbus and ath@pci to see if I
can stop them from printing 'ath0: device timeout'.

Turning off Tx interrupt mitigation with 'sysctl -w
hw.ath0.txintrperiod=1' helps widen the gap between timeouts from seconds
to minutes, but it does not stop them.

It looks like all interrupts (Rx & Tx) have ceased when a device timeout
occurs, and actual radio transmissions seem to stop, too.  However,
it looks like the DMA engine continues to mark descriptors on the Tx
ring as completed.

I have experimented with both the PCI exception reporting and PCI
performance parameters on my Soekris net45xx boards, and I see my
ath@pci on a net4526 report many "delayed transaction timeouts," which
indicates that one of my PCI devices does not play nice and retry PCI
transactions.  I am not sure, yet, if the Atheros adapter is guilty.
I am going to see if I can enable the same exception reporting on my
net4521's Cardbus bridge.

000:00:0: Advanced Micro Devices Elan SC520 System Controller (host bridge)
000:16:0: Atheros Communications AR5212 Wireless LAN (ethernet network, revision 0x01)
000:18:0: National Semiconductor DP83815 10/100 Ethernet (ethernet network)

Dave

-- 
David Young             OJC Technologies
dyoung@ojctech.com      Urbana, IL * (217) 278-3933 ext 24