asterisk users - Feb 2006 - Lots of lost interrupts when running HFC ISDN card in NT1 mode

Hi,

I'm setting up an asterisk server with this hardware configuration:

AMD Athlon 1000 Mhz
256 MB ram
3ware ATA raid controller
2 * Ethernet controller
2 * ISDN HFC controller

One ethernet controller is connected directly to the internet (public 
IP)
One ethernet controller is connected to the internal lan
One ISDN controller is connected to the public telephone network
One ISDN controller is connected to the internal S0 bus in NT mode

Software:
bristuff-0.3.0-PRE-1l, including asterisk 1.2.4 and zaphfc driver
zaphfc driver is patched with Florian Zumbiehl's patch to reduce 
interrupt load

Dialing into the box from the PSTN is no problem. Clear audio quality, 
no errors logged.

However, dialing into the box over the internal S0 bus is next to 
impossible. As soon as the call starts dozens of errors per second 
are logged to /var/log/messages:

Feb 15 22:56:39 office kernel: zaphfc: empty HDLC frame or bad CRC 
received (framelen = 5, stat = 0xff, card = 1).
Feb 15 22:56:39 office kernel: zaphfc: empty HDLC frame or bad CRC 
received (framelen = 3, stat = 0xff, card = 1).
Feb 15 22:56:47 office kernel: zaphfc: dropped audio (z1=7575, 
z2=7558, wanted 8 got 17, dropped 9).
Feb 15 23:31:57 office kernel: zaphfc[0]: received d channel frame 
with bad CRC.
Feb 15 23:31:57 office kernel: zaphfc[0]: empty HDLC frame received.

The card doesn't share interrupts. The card connected to the PSDN does 
share interrupts with the USB controllers.
The card in NT mode is used as the timer card: that's the one 
generating interrupts.

We've had the card working in another box, so I don't think it's a 
hardware problem.

Any clues on how to solve this problem?
-- 
Erik Hensema (erik@hensema.net)