nForce2 has more IRQs?

[Slaimus]

My friend's A7N8X shows max # of 22 for used IRQs under device manager in winxp. I thought IRQs are limited to 0-15?

 

[jiffylube1024]

Yeah it does. I'm running an Epox 8RDA+ and it also has 22. It's the newer "APIC" setting in the bios I believe that does it. This is also available on new Intel mobos as well. For example, I had an ASUS P4B266 that also supported this, as I'm sure the subsequent P4B533, P4PE, etc. all do.

 

[Zap]

Hardware IRQs are limited to 0-15, but Windows XP/2000 remaps them and allows more (don't know the technical details, but it seems to work). Perhaps someone else has more info on this?

 

[microAmp]

I have mine go up to 21 on a VIA chipset.....

WinXP for sure, don't remember about W2K now uses virtual IRQ's. IRQ conflicts are pretty much a thing of the past.

 

[AndyHui]

Hardware IRQs from 0-23 are available on most newer single processor chipsets which support the IO-APIC. Some APICs support even more IRQs.

The IO-APIC on these chipsets (all Intel i8xx, nForce, late VIA KxXXX chipsets, SIS P4 chipsets) is available for use with fully compliant ACPI BIOSes and Windows 2000 or Windows XP with the ACPI HAL.

Dual processor chipsets offer a lot more IRQs.

Note APIC and ACPI are different.

 

[Soulkeeper]

i remember that acpi apic whatever junk would remap everything to irc 8 and make things share
that caused a grip of problems for me and other people whose devices didn't like this
**

I could definately use more ircs tho

 

[Peter]

Originally posted by: Zap
Hardware IRQs are limited to 0-15, but Windows XP/2000 remaps them and allows more (don't know the technical details, but it seems to work). Perhaps someone else has more info on this?

No remapping going on. What you have there is a more advanced programmable interrupt controller (APIC) hardware (originally introduced for dual processor systems, but now found in any modern chipset). These have more than the 15 inputs offered by the legacy pair of PICs. Typically there are four to eight separate inputs for the PCI/AGP and integrated peripherals, separating them from the lower 16 where the legacy system peripherals connect. Serious server chipsets have many more interrupt inputs to the APIC controllers, up to over 100.

regards, Peter

PS: AndyHui, using APICs is not restricted to ACPI-supporting operating systems. There has been (and still is) the legacy "MPS" method for BIOS to describe an APIC-enabled system. Windows NT/2K/XP have an "MPS Uniprocessor" HAL that does use the APIC(s) then, and Linux usually goes for the MPS table too.

 

[AndyHui]

Thanks Peter.

 

[HdwGuy]

Not only does Windows remap IRQ it ingnores open and valid IRQ,s . Example on my system I have both serial ports disabled in BIOS. These normally take IRQ's 3 and 4. In XP it does not use 3 or 4 but insteed uses 22,and 23 for other devices. It works but is strange!

 

[Peter]

You didn't listen obviously. When running on APIC hardware, the PCI interrupt inputs are not routed to IRQ 0-15 anymore, they have their own dedicated inputs (numbers 16 and above). These are hardwired by chipset and mainboard design choices, and cannot be rerouted.

And besides, PCI devices that by said design choices physically attach to the same PCI interrupt line can NEVER be separated by software, no matter how many system interrupt vectors you have free.