PIRQ x Use IRQ No.

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

 

Quick Review of PIRQ x Use IRQ No.

The PIRQ x Use IRQ No. 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.

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.

 

Details of PIRQ x Use IRQ No.

The PIRQ x Use IRQ No. 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. The INT A entries are in bold to highlight the staggered arrangement.

Even then, you should try not use up paired slots that share the same set of IRQs. In this reference motherboard, such paired slots would be the AGP slot and PCI slot 1 or PCI slots 4 and 5. 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. For example, if you have a PCI network card in PCI slot 3, the table above shows that the slot’s primary PIRQ is PIRQ_2. Remember, all slots are first allocated INT A if it is available.
3. You can then select the IRQ you want by assigning the IRQ to the appropriate PIRQ. In our network card example, if the card requires IRQ 7, set PIRQ_2 to use IRQ 7. The BIOS will then allocate IRQ 7 to PCI slot 3. It is that easy! 🙂

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Just remember that the BIOS will always try to allocate the PIRQ linked to INT A for each slot. So, in our reference motherboard, the primary PIRQ for the AGP slot and PCI slot 1 is PIRQ_0 while the primary PIRQ for PCI slot 2 is PIRQ_1 and so on. 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. For example, Intel i8xx chipsets have 8 interrupt lines (INT A to INT H). In i8xx motherboards, the AGP slot will always have its own IRQ. Thanks to alex-the-cat for that info!

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