System Upgrade - AGP Video Board Broke the Network

System Upgrade - AGP Video Board Broke the Network
September 13, 2002

Well, I don't want to point fingers on this one - but it might even be a BOIS problem. At any rate,

Changing from a PCI video card to an AGP video card caused the network to stop working

(Hey, it only took 2 days to fix this one) :(

System Configuration

The relevant items are

Windows 98 with Service Pack 1
SMC EZ Card 10/100 PCI (SMC 1211 Series)
Matrox AGP Video card

This is basically the same configuration that had network problems before. Those were fixed by loading the OS service pack and getting new device drivers for the network card.

Symptoms

I could see the local machine in the network neighborhood. However, I could not see any other machines. Interestingly, the other machines could see the bad computer, but they were unable to view any of the shared files.

ping would not work either.

This indicated that the broken machine could broadcast its name over the network but could not do any other communication. Since it could browse its own files, I assumed that the network was correctly configured. Therefore, the logical conclusion was that either the driver software had a problem or that the hardware was broken so that it could only send data and not receive any.

Of course, I checked for new drivers (I already had them).

Experience has taught to always check the interrupts for conflicts. (In Windows 9x, use Start / Settings / Control Panel / System / Device Manager. Double click on Computer to see the interrupts. In Windows XP, use Control Panel / System Properties / Hardware / Device Manager / View Resources. In most systems, the keyboard combination Windows-Break is a shortcut to the Device Manager.) The Network card and the AGP card were both using interrupt 12. Under PNP (Plug-And-Play), that's not supposed to matter. Supposedly, several hardware devices can share a single interrupt. (In your dreams.)

Sometimes it is possible to change the interrupt assignments via software. In Device Manager, under either Display Adapters or Network Adapters, double click on the adapter and select Resources. The general procedure is to uncheck "Use automatic settings", highlight the interrupt, and press the "Change Settings" button. Of course, neither device would let me change the interrupt.

(I really miss the old days when interrupts were set by board jumpers. Then you had control of these things - IF you had the documentation. With PNP, you are at the mercy of some programmer who never tested a system just like yours.)

At this point, I still did not know what the actual problem was. Interrupts were still just a guess - it could have been anything.

The Fix

This is unbelievable - I moved the network card from slot 1 to slot 2.

Now the AGP card uses interrupt 12, the network card uses interrupt 10, and the system works.

Apparently, PCI interrupts are assigned based on what slot the card is plugged into.

By the way, in finding this solution I went down may dead ends and tried many things not documented here. It was not as simple as this writeup makes it sound. The final clue was that one web page suggested that some BIOS's allow you to assign specific interrupts to specific slots. Well, my BIOS does not work that way, so I just decided to move the card and see what happens. (So again, I was lucky. I guess that if you are lucky a lot, it's called skill.)

Author: Robert Clemenzi - clemenzi@cpcug.org