[asterisk-ss7] Strange interrupt issue with zaptel and chan_ss7

Kai Militzer km at westend.com
Fri Jul 7 02:10:58 MST 2006

Hello everyone,

I have a very strange issue with a TE205P, zaptel and chan_ss7 regarding 
interrupts. As I think this is originated somehwere in the zaptel 
driver, I crosspost this to -dev, hope that's OK.

As chan_ss7 need not d-channel, the configuration in /etc/zaptel.conf is 
as follows:


That's the first difference to a config with zaptel, where dchannels 
need to be configured.

I came across the issue, when I started to get a lot of CRC16 errors on 
the MTP2 part of chan_ss7 resulting at last in a flapping of the 
complete SS7 signaling every few minutes. Together with these CRC16 
errors I got messages, that chan_ss7 ran into an "Excessive poll delay" 
and that the Zaptel input buffer went full, directly followed by a empty 
zaptel output buffer. What was/is strange is the fact, that I have two 
machines configured the same, only differing in DPC and OPC codes in 
chan_ss7 and different CPUs. The machine working without problems runs 
with a AMD Duron with 1300 MHz, the one with the CRC-errors on a P4 with 

My first step to find the source of the problem was to put the Card into 
a different System, also running a P4, but this time only with 1.8GHz. 
That resulted in the same errors, the SS7 part wouldn't even start with 
that one.

So I started to dig deeper. I made a crosslink cable and connected two 
E1 ports with it, started two instances of asterisk with chan_ss7 and 
experienced the problem (that proved at last, that there was no problem 
with the Switch from the TelCo). So my next step was to start the two 
instances with chan_zap instead of chan_ss7 and everything is fine. No 
erros in any way.

As I knew, that the Card in my other system with an AMD worked, I now 
changed Hardware again, this time putting the card in AMD Athlon XP 
3000+, crosslinked the two E1s again and started two instances of 
asterisk running chan_ss7. And voila, no problem. At least at first it 
looked this way. I let it run over night (only asterisk is running, no 
traffic or whatsoever may distract the system) and when I came back this 
morning, I had CRC errors + the other error messages on the screen. So 
now I suspected the card (which I still do for a bit). To test, if the 
TE205P works as it should, I made a crossover plug (Pin 1-4 and 2-5) and 
ran a patlooptest, a loop test with zttool, a zttest and also 
uncommented #define CONFIG_ZAPTEL_WATCHDOG in zconfig.h. All looks fine, 
  no errors whatsoever. The card is assigned an interrupt for itself 
without anything else using it. All looked good.

Then finaly I came across the behavior that puzzles me. Asterisk was 
running with two instances over the crosslink and the console screen was 
blanked on the console. So I wanted to press Shift to unblank it, but 
accidently pressed the CapsLock key. When the screen was unblanked and I 
  started to type, I realized, that CapLock was on. I pressed it again 
and in this moment, I got a CRC16 error. I thought that was strange and 
pressed it again twice, and there it was again, Packets from the zaptel 
driver to chan_ss7 got lost. The same behavior happens, when I press 
ScollLock or NumLock. The Keyboard runs on interrupt 1 and the TE205P on 
IRQ11, so there shouldn't be any impact when the keyboard uses this 

As you can see, I am stuck now, why does this happen and why only with 
chan_ss7? I cannot say if I can reproduce the errors on my "running 
system" (the one without the errors) as it is located elswhere without a 
keyboard connected. Any ideas how to solve this are greatly appreciated, 
as I need to get the system back to work.

Best regards,

Kai Militzer                 WESTEND GmbH  |  Internet-Business-Provider
Technik                      CISCO Systems Partner - Authorized Reseller
                              Lütticher Straße 10      Tel 0241/701333-14
km at westend.com               D-52064 Aachen              Fax 0241/911879

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