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W2K Plug and Play

Why are all my devices on a single IRQ? by TestNode
Posted: 7 Aug 01

Microsoft and several of the system manufacturers devised a protocol named ACPI (Advanced Configuration and Power Interface). To obtain a Made for Windows 2000 logo, a manufacturer must meet the ACPI standard and allow Windows 2000 to manage this device.

There are many PCI cards do not meet this standard, common cards that are commonly useful, like the 3COM905b networking card, or the Adaptec 2940 series of SCSI card. These hardware devices do not understand ACPI, they were designed long before that standard was implemented. A potential problem found later might be created at the point of installation. The installation process does not enumerate the devices in your PC. The installation process looks at the BIOS and looks for ACPI flags, then it checks against a list of known bad ACPI BIOS implementations, then finally checks against the BIOS date. If your BIOS is dated 1/1/1999 or newer, then the ACPI HAL is installed by default, regardless of whether your devices actually understand what ACPI is.

The type of problem created here is one of communication. The card manufacturers designed their device communications based on the PCI standard and would communicate through the system BIOS to exchange messages and data. In Windows NT 4.0 these messages were intercepted, but the OS was true to the BIOS manner of communicating and used the interrupts assigned by the BIOS. Windows 2000 adds a layer of complexity by not just intercepting messages, but translating these messages and rerouting them. A request for sound gets routed to IRQ 9, then a table lookup occurs and the the request is routed to IRQ 12. This is an implementation of a virtual address table, in this case a virtual device table. Very slick stuff, but there can be delays.

The implementation of ACPI allows W2k to work very well on laptops, and is intended to remove all issues of device contention or IRQ conflict. It is a step beyond Plug and Play. It works very well in systems designed for ACPI, or with devices designed for ACPI. However, if you have older devices the delays created by the virtual device lookups may cause mysterious, annoying problems. You may find device timeout messages in the event log, your machine may seem to remove itself from the network or domain, or your sound may be choppy, broken, or silent.

If you have system problems that you cannot resolve, or if you are attempting to change a device IRQ and cannot, consider removing the ACPI HAL and installing the Standard PC HAL. This method is not supported or offered by Microsoft, it is a solution I created and implemented through trial and error (testing).

The only way to change your IRQ is to remove ACPI. The only way to remove ACPI, is too remove the ACPI HAL and that requires a repair install and then some configuration.

First, have your Windows 2000 CD and all the information about your peripheral card that you can gather. The more info you get, the less experimenting you will have to do to configure IRQs.

Here is the process:

1. Insert your Windows 2000 CD into your CD drive and reboot.

2. Make certain that your BIOS is set to boot to the CD. (Read the manual for this info)

3. When Windows 2000 first turns the screen blue and writes in the status area, "Press F6 if you have....". Press F5 now! **Yeah thats odd, but thats the way it is.**

4. you will be presented a screen that contains a list of PC configurations - choose Standard PC.

5. Continue through the installation, doing a repair install. DO NOT ABORT THIS INSTALLATION! your system will not boot if you don't.

6. Reinstall your service pack level.

7. Right click on my computer and select Properties, choose Hardware, then choose the Device Manager. Click the plus sign next to Computer and right click on Standard PC - click Properties.

8. Click on IRQ Steering. You will see three boxes checked. FROM THE BOTTOM UP, uncheck these boxes.

9. You will be prompted to reboot. Do so...

Now the hard or easy part, I can't say.

PCI devices today are loaded with IRQ presets. Manufacturers have agreed to use certain IRQs for their devices. For instance sound card traditionally used IRQ 5. Unfortunately, Sound Blaster decided to break this habit, my current SB Live uses IRQ 12.

If your problem remains, it may now be the possibility of real IRQ conflicts - depending on your devices.

The most extreme manner of sorting out IRQ issues is this:

Remove all peripheral cards except for the video card, and your hard disk controller if that is on a PCI card. Boot Windows 2000, open Device Manager and set this card to use the desired IRQ. Shut down and readd your cards one by one, rebooting between each and setting the IRQ for each - or just accept where Windows 2000 slots them.

Back to Microsoft: Windows FAQ Index
Back to Microsoft: Windows Forum

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