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PIRQ x Use IRQ No.

Common Options : Auto, 3, 4, 5, 7, 9, 10, 11, 12, 14, 15

Quick Review

This BIOS feature allows you to manually set the IRQ for a particular device installed on the AGP and PCI buses.

It is especially useful when you are transferring a hard disk from one computer to another; and you don't want to reinstall your operating system to redetect the IRQ settings. By setting the IRQs to fit the original settings, you can circumvent a lot of configuration problems after installing the hard disk in a new system. However, this is only true for non-ACPI systems.

Here are some important notes from the reference motherboard (may vary from motherboard to motherboard) :-

  • If you specify a particular IRQ here, you can't specify the same IRQ for the ISA bus. If you do, you will cause a hardware conflict.
  • Each PCI slot is capable of activating up to 4 interrupts - INT A, INT B, INT C and INT D.
  • The AGP slot is capable of activating up to 2 interrupts - INT A and INT B.
  • Normally, each slot is allocated INT A. The other interrupts are reserves and used only when the PCI/AGP device requires more than one IRQ or if the IRQ requested has been used up.
  • The AGP slot and PCI slot #1 share the same IRQ.
  • PCI slot #4 and #5 share the same IRQs.
  • USB uses PIRQ_4.

Below is a table showing the relationship between PIRQ and INT in the reference motherboard :-

Signals

AGP Slot
PCI Slot 1

PCI Slot 2

PCI Slot 3

PCI Slot 4
PCI Slot 5

PIRQ_0

INT A

INT D

INT C

INT B

PIRQ_1

INT B

INT A

INT D

INT C

PIRQ_2

INT C

INT B

INT A

INT D

PIRQ_3

INT D

INT C

INT B

INT A

You will notice that the interrupts are staggered so that conflicts do not happen easily.

Even then, you should try not use up paired slots that share the same set of IRQs. In such cases, it is recommended that you use only one of the two slots.

In most cases, you should just leave the setting as Auto. This allows the motherboard to assign the IRQs automatically. But if you need to assign a particular IRQ to a device on the AGP or PCI bus, here is how you can make use of this BIOS feature.

  1. Determine the slot that the device is located in.
  2. Check your motherboard's PIRQ table (in the manual) to determine the slot's primary PIRQ.
  3. You can then select the IRQ you want by assigning the IRQ to the appropriate PIRQ.

Just remember that the BIOS will always try to allocate the PIRQ linked to INT A for each slot. It is just a matter of linking the IRQ you want to the correct PIRQ for that slot.

Please note the table, notes and INT details are only examples provided by the reference motherboard. They may vary from motherboard to motherboard.

 

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