IRQ SLEUTH GUIDE
2007 Version
Some video capture hardware (notably the DPS Perception Video Recorder and its cousin audio card the A4V) are extremely reluctant to share IRQ resources. What are IRQ's you ask? This stands for "Interrupt Request". In "Wintel" architecture computers there are 15 channels through which hardware devices can get the processor's attention - to interrupt it and say, "excuse me, this user here wants you to do something." Hence it's called an Interrupt Request. While there are actually 15 IRQ channels, ONLY 4 of them can be assigned to the PCI bus - the slots where you plug your cards in. Since computers these days generally have more than 4 PCI slots, and the AGP graphic slot, onboard USB, 1394 "Firewire" and SCSI ALSO use the PCI bus, there's a whole lotta sharin' goin' on!. What you have to do is figure out which slot(s) do not share with anything else and locate your IRQ sensitive hardware there.
First, if you have everything installed and it's all working OK, then Bill Gates has performed a miracle and you can get to work and make some money. As they say, "if it ain't broke don't fix it". But if you've installed a 1394 card and it works, but your network card just quit...or if you turned on USB and suddenly your sound doesn't work, THEN it's time to do IRQ sleuthing.
[NOTE: This applies to older computers WITHOUT PCI-e slots. We have not had these problems on machines with PCI-E, but then we have not installed legacy hardware in a PCI-e machine. These steps may work with PCI-e, but try them at your own risk.]
Start by getting a flashlight and looking inside your computer. The slot with your video card that is set back aways from the others is known as the AGP slot, for Advanced Graphics Port. The PCI slot next to it is usually slot #1. Most motherboards have the slot numbers etched near the slots. Write down which cards are in which slots.
Next, see what Windows says about your IRQs. You'll want to find the System Information applet, which resides in various places depending on your OS:
In Windows NT, START | administrative tools-common | Windows NT Diagnostics | Resources tab.
In WXP/Vista: Start | Run | then type "msinfo32.exe"
Once you get to System Info, click on Hardware Resources and choose IRQs. If your numbers go 1 to 15 (maybe skipping a few in between), you're going to be able to manually control things. If everything on the PCI bus uses the same IRQ (often #9) or your IRQ numbers go above 15 (known as "vector IRQs") this means you have the Advanced Configuration automatically controlling things. The bad news is you're probably going to have to reinstall Windows (see below). Regardless, check to see if all your components are listed and write down what you see. In W2k and XP you can also check the Conflicts/Sharing and see what it reports on IRQ and memory address spaces that are shared.
Next, it's time to reboot and see what BIOS says.
(An aside to computer neophites: BIOS stands for Basic Input-Output System, and it's the code programmed into a chip that is on your motherboard that controls all this basic stuff. It assigns IRQs to various components, turns on or off features on the motherboard, controls voltages and clock speed to the processor, and a whole lot more. The BIOS is also known as a "chipset", and there are several vendors, including Phoenix, AMI, Intel, and Via. Via is most commonly found in AMD computers.)
When you reboot, watch the BIOS talk to you as it does its memory check, scan for disks, etc. (If you have a name-brand store bought system from Compaq, IBM or HP you may have a problem with this - if when you first turn the machine on you see a big red 'Compaq' or other splash screen, try hitting Esc, or if it flahes "Press [X] to see BIOS Progress" or some such thing, then you should be able to see the BIOS checking memory and other things.) At the end, just before you get the OS chooser screen, most BIOSs will flash a full-screen report. When it appears hit the PAUSE key on the keyboard so you can study this report. It should contain system setting information for all the resources in use. At the top you'll see parallel and serial addresses and IRQs. At the bottom you should see the IRQ status of all your installed PCI cards and onboard devices. If you've noted which card is in which slot, you can determine what "real" IRQ each one is using, even if Windows reports a vector number. (If no IRQ is listed, that device doesn't use one.) If you see two devices using the same IRQ, you may have trouble - read on.
Now on your sheet of paper you should be able to map which IRQs are assigned to which slots, and which slots share with onboard devices. Find a slot that has an IRQ all its own and move your IRQ-sensitive device there. You will have to shuffle cards around.
This MIGHT be enough to solve the problem, but if you shuffle cards and the IRQs change, or if all your PCI components are on the same IRQ, you're going to have to take control over BIOS. Here's how:
MANUAL CONTROL (NOT ADVISED UNDER VISTA)
Reboot the machine and go into BIOS Setup. How you do that depends on the BIOS. Most have you hit Delete, but some use F2 or F10. If you're unsure, during the first few seconds of booting, hit all the function keys and one of them should work. Or you COULD look in your user manual.
Anyway once you're into BIOS, look for a PCI setting category. If you DON'T have a PCI setting category, shut down, remove your video hardware, and give this box to your kids to use for games or your secretary for word processing. Consumer-grade Compaq's, for instance, have very little that is user controllable in BIOS. That helps keep prying fingers from screwing things us, but that doesn't help when you have to control sharing.
OK, if you have a good BIOS, in PCI/PNP setup, you should find a place to assign IRQs to the PCI slots. They're probably all set to auto. If you see something like mine that says "slot 1&4", that's an instant clue that slot 1 and 4 are hard-wired to share an IRQ. So you can only use slot 1 or 4 if you have devices that need dedicated IRQs. (You can use a device in both slots if one of the cards does not use an IRQ.)
For the four Interrupts, A, B, C, and D, select unused IRQs. BIOS won't tell you which ones are already in use, so you'll have to make an intelligent guess, Usually, 5, 9, 10, and 11 are available. Standard configuration assigns the following permanently, so don't use them:
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1 - a system IRQ
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2 - duplicates 9, so don't use unless you don't use 9
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3 - Serial 2
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4 - Serial 1
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6 - Floppy
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7 - Parallel Printer Port
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9 - (see 2)
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12 - Commonly used for mouse
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13 - Occupied
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14 - Primary IDE
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15 - Secondary IDE
If you don't use the onboard mouse port or you use only one serial port, you can turn those resources off in BIOS and those IRQs will be available for assignment to your PCI slots.
If you have AGP or other onboard PCI resources like SCSI, you will have more "mystery shares", because each of those resources also share with a PCI slot. Most of the time motherboard manuals or BIOS settings don't tell you which slots share which resources, so you have to figure it out the hard way. Basically, save your configuration, reboot, and look at the BIOS report again to determine the true shares. You may need to shuffle boards around again to get the sharing-sensitive boards on their own IRQs.
Now your computer should be happy and everything works fine..
BUT!!!
If Windows detects that Automatic Power and Configuration Interface, you might still be in trouble, because Windows will think it knows more than you do, and shuffle around IRQs again and keep things from working. So if you have BIOS telling you things are clear, but Windows System Information gives you a different IRQ readout after making manual assignments, then you're going to have to reinstall Windows. Fortunately a Repair Reinstall will do this trick, so you won't have to reinstall your applications
TO REINSTALL
Make sure your BIOS is set to boot from CD. Put your Windows XP or 2k disk in and boot from the CD. When the Installer asks "Press F6 to install additional stuff", press F5 instead. You'll soon see a chooser screen to choose the type of computer this is. Use the arrow keys to scroll the list and highlight MPC Multiprocessor PC (assuming yours is a multiprocessor - use Uniprocessor if you have only one processor). Then continue the installation. At the first prompt for "Repair using the Recovery Console", chose to Continue and not repair. At the second prompt, after it finds the existing 2K or XP install, choose R for Repair. Once it's done, everything should be back to normal, though you should reinstall any service packs. This will force Windows to ignore the APCI stuff and your BIOS IRQs should match the Windows IRQs.
NOTE: THIS HAS NOT BEEN TESTED WITH WINDOWS VISTA! (We recommend you NOT switch to Vista if you have hardware that requires special IRQ configuration.)
FINALLY
Some devices will share with finicky ones! I've successfully installed a combo 1394/USB controller in the PVR system in a slot that shares with the Matrox G400 video card (it happens to be the only empty slot). This device uses a PCI Bridge controller, which extends the PCI bus to the two devices on the board, and the bridge shares with the normally-finicky sound card and works OK. So the moral to the story is...Your Mileage May Vary. This can get very complicated, and it can be very easy. So roll up your sleeves, get out the timing light and socket set, plugs & points, and tune this puppy up. You can't learn if you don't dig in and do it.
Just remember: if it ain't broke, don't fix it!!!
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