IRQ Troubles on Razor

The Dell Dimension 4560, a.k.a. razor, that controls my Sherline CNC mill woke up without network support. That’s a showstopper, because all the G-Code files live on the server across the basement.

All my boxes have a network function dipstick test: the desktop background is an image on that same file server. When the NFS share wakes up dead, then the screen shows the default Ubuntu background: brown = down! (At least in Ubuntu 8.04 LTS, which is what EMC2 is built on right now.)


  • NFS share isn’t mounted
  • … and can’t be mounted
  • ifconfig shows eth0 up & active
  • can’t ping the server
  • can’t ping razor from the server
  • Link lights on network switch nailed to floor joist overhead are green
  • Link light on NIC on back panel
  • Activity lights on switch & NIC blink occasionally (??)
  • Swapping ports on the switch = no change
  • Laptop works fine plugged into switch = switch OK

So whatever is busted, is busted in the 4560. Drat!

(Should have checked cable between switch and NIC. Sometimes you get a data failure without affecting the link & activity lights. Weird, but stuff happens.)

Looking in dmesg shows that a bogus IRQ 11 occurred during startup:

[   44.439932] irq 11: nobody cared (try booting with the  irqpoll" option)
... time passes ...
... bad IRQ log dump gibberish ...
[   44.440440] Disabling IRQ #11

Fairly obviously, after that point nothing about the NIC or anything else on IRQ 11 will work: the hardware setup may be OK, you can write to it and read from it, but no actual data gets through.

A reboot didn’t cure the problem. Reboots in Linux rarely solve a problem; you’ve got to actually find the root cause and fix it, rather than shake the dice to see if a better combination comes up.


Restarted to get into Dell’s attenuated BIOS configuration routine, changed the NIC to IRQ 3 (just because it was first on the list), saved, restarted, and everything works. The bogus interrupt is gone, the NIC is running, NFS shares are OK.

It absolutely beats me. But at least this is written down so the next time it happens, I’ll remember what I did.

Oh, yeah. The Sherline CNC mill uses stepping motors and uses cutters, so it’s a Steppin’ Razor, of course, and is therefore named razor. I suppose I could have called it molly, but that’d be a stretch.