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irq holder for pci steering

Posted on 1998-12-25
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would you please give a thorough, yet clear cut explanation as to exactly what this term means and what it does in the
PC's operation? Many thanks for all you can do to clarify tis subject.
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Question by:kerryc
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11 Comments
 
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Expert Comment

by:istal112898
ID: 1760705
The  'Irq-Holder for PCI-Steering' is just the 'device' that manages
the PCI sharing for your PCI devices. ---> Ignore them and everything
is fine.
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Expert Comment

by:istal112898
ID: 1760706
This is a mechanism for IRQ sharing between PCI cards.
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Expert Comment

by:istal112898
ID: 1760707
When you have a PnP PCI card in your system, Windows 95 automatically adds the IRQ-Holder for PCI Steering for each one. It is normal.
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Author Comment

by:kerryc
ID: 1760708
Too simplistic, I needed to gain an understanding of this subject as I asked in my original question. Although the reply belayed any anxiety over what the significance of this term is, it did not explain to me what exactly it is or how it fits in to the overall functon of win'95 etc...
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Author Comment

by:kerryc
ID: 1760709
Lets get a real tangable handle on how this thing works!
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Expert Comment

by:istal112898
ID: 1760710
there is not more than it does. that is all the function it does. what exactly you want?
IRQ is for VIDEO CARD, SOUND CARD,MODEM, those are the main IRQ PCI STEERING. it just make sure that the device communicate correctly. IRQ holder means that it will keep or share that IRQ with other devices like cascading . 2 or 9 or above. will depend on the device for that.
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Expert Comment

by:rmarotta
ID: 1760711
kerrc,
You might find the following article of interest:

http://www.idg.net/idg_frames/english/content.cgi?vc=docid_9-53174.html

I hope it helps.
Regards,
Ralph
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Accepted Solution

by:
MATTCEI earned 800 total points
ID: 1760712
Everything you always wanted to know about PCI IRQ Steering,from Microsoft:

Description of PCI Bus IRQ Steering     Article ID: Q182604
 
     Windows 95 OEM Service Release 2 (OSR2) and Windows 98 provide support for PCI bus IRQ steering.
     By using PCI bus IRQ steering, Windows can dynamically assign or "steer" PCI bus IRQs to PCI devices.
     Note that Microsoft Windows 95 (retail release) and Microsoft Windows 95 OEM Service Release 1
     (OSR1) do not provide support for PCI bus IRQ steering.

     ISA and PCI IRQs

     Multiple Industry Standard Architecture (ISA) devices cannot share an ISA IRQ, however, multiple PCI
     devices can share a PCI IRQ. On computers that use a PCI bus, the 16 standard IRQs can be
     programmed to either PCI or ISA mode. An IRQ cannot be programmed for both modes at once.

     How IRQs Are Assigned to PCI Devices

     In Windows 95 (retail release) and OSR1, the Basic Input/Output System (BIOS) assigns IRQs to PCI
     devices. With OSR2 and Windows 98, if PCI bus IRQ steering is disabled in Windows the BIOS assigns
     IRQs to PCI devices, but if PCI bus IRQ steering is enabled, Windows assigns IRQs to PCI devices.
     When IRQ steering is enabled the BIOS still assigns IRQs to PCI devices, and even though Windows
     has the ability to change these settings, it generally does not.

     CardBus Cards and OSR2

     PCI R3 Personal Computer Memory Card International Association (PCMCIA) cards (CardBus cards),
     look very similar to the more common ISA R2 PCMCIA cards. CardBus cards use 32-bit addressing and
     require a PCI-type shareable IRQ. R2 PCMCIA cards use 16-bit addressing with an ISA-type non-
     shareable IRQ. PCI bus IRQ steering gives the operating system the flexibility to reprogram PCI IRQs
     when it rebalances Plug and Play resources. Without PCI bus IRQ steering, Windows can only
     rebalance Plug and Play ISA IRQs to resolve resource conflicts.

     How OSR2 and Windows 98 Use PCI Bus IRQ Steering

     PCI bus IRQ steering gives OSR2 and Windows 98 the flexibility to reprogram PCI interrupts when
     rebalancing Plug and Play PCI and ISA resources around non-Plug and Play ISA devices. Windows 95
     (retail release) and OSR1 cannot rebalance PCI and ISA IRQs for Plug and Play devices around
     non-Plug and Play ISA devices to solve resource conflicts.

     For example, if your computer's BIOS is unaware of non-Plug and Play ISA cards, the operating system
     does not have PCI bus IRQ steering, and 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 the operating system can resolve this IRQ resource conflict. To do
     so, the operating system:

          Disables the PCI device.
          Reprograms a free IRQ to a PCI IRQ, for example IRQ 11.
          Assigns an IRQ holder to IRQ 11.
          Moves the PCI device to IRQ 11.
          Reprograms IRQ 10 to be an ISA IRQ.
          Removes the IRQ holder for IRQ 10.

     IRQ Holder

     An IRQ Holder for PCI Steering may be displayed when you view the System Devices branch of Device
     Manager. An IRQ Holder for PCI Steering indicates that an IRQ has been programmed to PCI mode and
     is unavailable for ISA devices, even if no PCI devices are currently using the IRQ. To view IRQs that
     are programmed for PCI-mode, follow these steps:

        1.Click Start, point to Settings, click Control Panel, and then double-click System.

        2.Click the Device Manager tab.

        3.Double-click the System Devices branch.

        4.Double-click the IRQ Holder for PCI Steering you want to view, and then click the Resources
          tab.

     How to Determine if Your Computer Is Using IRQ Steering

     To determine if your computer is using IRQ Steering, follow these steps:

        1.Click Start, point to Settings, click Control Panel, and then double-click System.

        2.Click the Device Manager tab.

        3.Double-click the System Devices branch.

        4.Double-click PCI Bus, and then click the IRQ Steering tab. You should see one of the following
          settings:

              - IRQ Steering Enabled
              - IRQ Steering Disabled

     NOTE: PCI bus IRQ steering is disabled by default in OSR2. If you are using OSR2, and IRQ steering is
     disabled, verify that the Use IRQ Steering check box is selected on the IRQ Steering tab.

     IRQ Steering may be displayed as disabled in Device Manager for any of the following reasons:

          The IRQ routing table that must be provided by the BIOS to the operating system may be
          missing or contain errors. The IRQ routing table provides information on how the motherboard is
          configured for PCI IRQ's.
          The Use IRQ Steering check box is not selected.
          The "Get IRQ table from Protected Mode PCIBIOS 2.1 call" check box is not selected.
          Your computers BIOS may not support PCI bus IRQ steering. For more information, contact the
          manufacturer of your BIOS.
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Expert Comment

by:istal112898
ID: 1760713
that's a cool answer. Give MATTCEI the points. :)
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Expert Comment

by:bushhead
ID: 1760714
agreed. it is a good answer, maybe give microsoft some points as well.

bush
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Author Comment

by:kerryc
ID: 1760715
That was an excellent answer, In fact it went on to clarify some related points! Much appreciated!!
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