Hi Marc

At 16:52 10/3/99 , you wrote:
 > Can somebody tell me what PCI Steering is? Every time I run Nuts
 > and Bolts diagnostics, I get this message: "IRQ holder for PCI
 > steering has been disabled."

PCI bus IRQ Steering is an artifice used by Win95b and Win98 [**]
to override the IRQ assigned by the motherboard BIOS to any PCI
device. It is perfectly normal to have one or more instances of
"IRQ Holder for PCI Steering" in Device Manager. These instances
of "IRQ Holder for PCI Steering" do not indicate IRQ conflicts.

[**]  In Win95 and Win95a (OSR1), the IRQs assigned to PCI
       devices by the motherboard BIOS could not be changed.

"PCI bus IRQ steering" allows Windows to give IRQs to PCI devices
that are normally given to Plug and Play ISA devices. (ISA slots
are the other "longer" slots on your motherboard.) This gives
Windows flexibility in rebalancing Plug and Play PCI and ISA
resources around non-Plug and Play ISA devices.

If you go to Device Manager and double-click the System Devices
branch, then the PCI Bus, and then click the IRQ Steering tab,
you should see either "IRQ Steering Enabled" or "IRQ Steering
Disabled". You can turn it on or off. Make sure it is enabled...
maybe things will work better. On my systems, disabling PCI
steering does not get rid of the instances of "IRQ Holder for
PCI Steering" in Device Manager.

 > I'm trying to install a Creative Vibra 128 soundcard (PCI) on
 > Win 98 and it chooses IRQ 12, which I think is conflicting
 > (PCI steering uses IRQ 11 and 12).

Is your video card using IRQ 12? Is any other device? Perhaps
your sound card was not designed to use IRQ 12. In theory, PCI
devices are supposed to be able to share IRQs, but in practice,
some devices do not work when their IRQ is shared. (However,
as I mentioned above, the fact that an IRQ has been assigned
as "IRQ Steering Enabled" does not necessarily mean the IRQ
is shared.)

Motherboard manufacturers often hard wire two PCI or AGP slots
to use the same IRQ. Using the BIOS to change the IRQ assigned
to one of these slots unfortunately changes the IRQ of the
other slot as well. In other words, you can't get these two
slots to use different IRQs. In my experience, Windows' IRQ
steering often (always?) cannot get two such slots to use
different IRQs.

Important:

You may have to open the case and physically move your sound
card to a different PCI slot. In my experience, this is often
the only way to resolve apparent IRQ resource conflicts.
Consider also that your sound card might only work with certain
particular IRQ, Input/Output, DMA, or Memory ranges. Windows
may assign a free resource to a device that the device was not
designed to work with. Unfortunately, juggling the PCI cards
in different PCI slots is a fact of life with some motherboards
and devices.

More on PCI Steering:

When Windows is loading and decides that it must give a PCI
device a different IRQ from the one already assigned to it by
the system BIOS, it first disables the PCI device and then goes
about obtaining an IRQ for it by reprogramming an ISA type IRQ
to a PCI type IRQ. It assigns an IRQ holder to this IRQ which
is used during the time that the PCI device is being reenabled
and given the newly reprogrammed IRQ.

As an example of how this all works, suppose your computer's
BIOS is unaware of non-Plug and Play ISA cards and you are using
either the original Win95 or Win95a. If the BIOS has set a PCI
device to IRQ 10, you may have a resource conflict when you add
a non-Plug and Play ISA device that is configured for IRQ 10.

However, with PCI bus IRQ steering, Windows can resolve this
IRQ resource conflict. To do so, Windows first disables the PCI
device and reprograms a free IRQ to be a PCI IRQ, for example
IRQ 11. Then it assigns an "IRQ holder" to IRQ 11 and then moves
the PCI device to IRQ 11. Finally it reprograms IRQ 10 to be an
ISA IRQ and removes the IRQ holder for IRQ 10.

If an IRQ Holder for PCI Steering is displayed when you view
the System Devices branch of Device Manager, it indicates that
an IRQ has been programmed to PCI mode and is *unavailable for
ISA devices*, even if no PCI devices are currently using that
IRQ.

Regards,
Bill

               PCBUILD mailing list is brought to you by:
                            The NOSPIN Group
                  http://nospin.com - http://nospin.org