Assigning IRQs

[Squally Leonharty]

Hello there,

I've recently moved one (and the only) PCI card to another slot and that caused IRQ 16 to be assigned to it. The problem is that IRQ 16 also has the graphics card and the firewire controller. Is there any way to assign IRQ values manually in the BIOS? I'm not very familiar with this, so any help would be appreciated.

I could move the PCI card to yet another slot (fair enough for me), but I'd still like to try assigning IRQ values first, because the current location of the PCI card is optimal for the graphics card and the air flow through the case.

Edit: The PCI card is a HDD controller: Promise Ultra133 TX2.

 

[LTC8K6]

If you are running XP, it is entirely normal for IRQ's to be shared and it should cause no problems.

You didn't mention any problems....

 

[Peter]

It is normal for IRQs to be shared IN EVERY OPERATING SYSTEM. The PCI interrupt system has been designed to be like this.

Besides, if a modern PC is running on the APIC interrupt controllers, then there isn't even any IRQ routing going on. Everything is connected in hardware, hardwired to be on the APIC-IRQ input line the mainboard designer thought is good for each device. Again, if there's device sharing going on, it's meant to be this way and it's OK like that.

Just leave it alone. Accept the fact that shared IRQs are not a problem, despite the fact that there are still thousands of FAQs, support drones and other firm believers that tell you otherwise.

 

[Squally Leonharty]

Thing is that before I moved the card, it had a different IRQ assigned. Normally, a graphics card, especially more powerful ones, should be on a dedicated IRQ in order to prevent conflicts during hefty gaming or whatever stresses the graphics card. That reminds me of the old days with Windows 98. xD

Anyway, I guess I shouldn't worry too much about it then. I'll still try moving around the card, though. There is another possibility in the cards' positioning I'd like to try. Who knows that solves it, otherwise I'll just live with it.

Thanks for the replies!

 

[Peter]

Shared IRQs neither are nor cause "conflicts". Not even in Windows 98. As I said, don't believe the myth spinners.

There is nothing to "solve" either. Just leave it alone.

 

[imported_Harbinger]

Well , you dont have to worry since these IRQs are virtual. Nowadays hardware-physical IRQs in bios are reserved for internal mobo parts like clock, keyboard, floppy controller etc. Because of early IRQ number limitation microsoft had to create virtual IRQs in their OS's thus IRQs are controlled and assigned automatically by windows without causing any conflicts. Under DOS though it would be a different story \]

In fact my 6800GT, Audigy 2ZS and Firewire Controller use IRQ 16 Nice coincidence

 

[Squally Leonharty]

Heh, I see. Thanks for the replies. Now my motherboard only has to wait before it can embrace the new Leadtek graphics card. It has still not arrived yet, because it's extremely rare in the Netherlands. Neither the store nor their vendor have it in stock, so it goes all the way back to Leadtek. I wonder it has to be manufactured specially for me?

 

[Peter]

The IRQs aren't "virtual", and they aren't assigned by the OS. They're hardware IRQs, directly routed (by mainboard design) onto the multiple inputs of one or more "APIC" interrupt controllers. These are not limited to the 15 inputs available on the legacy pair of PICs, hence the higher IRQ numbers. Your average desktop chipset has something between 20 and 32 interrupt lines when running APIC mode; server chipsets have many more, easily 100 dedicated IRQ inputs. Still, sharing happens even on those.
For compatibility, the PIC pair is still there and wired up, to let APIC-unaware operating systems still run fine.

APIC mode is a prerequisite to running more than one CPU, hence it's found in many recent chipsets - even if the board implements just one CPU. HyperThreading pseudo-dual CPU mode also requires APIC mode.

 

[LTC8K6]

If it aint broke, don't fix it!

 

[anandMike]

Silly question, but is this what is done when you tell your m/b that a plug and play OS is installed?

The implementation of these IRQ's went completely by me. I knew the old stuff inside and out, but when a guy called me today and said the modem was on IRQ 17, I went looking and boy was I surprised ...

Mike

 

[Peter]

Nope, the "PnP OS installed" switch just changes how BIOS initialises ISA (!) PnP cards. If you say "Yes" here, only those that are potentially needed for boot are initialized and the rest left to Windows; if you say "No", then BIOS initialises and enables everything. The latter is to be preferred even if you do have a PnP OS installed - BIOS knows better.

IRQ line numbers above 15 occur whenever the system is using modern interrupt controller(s) instead of the ancient pair of ISA interrupt controllers. See my above post on the "virtual IRQ" myth and the reality behind it.

 

[Skoop]

Why exactly do you want to use this PCI card? Your motherboard has an on-board Promise controller that will support U133.