IRQ issues with AMD/VIA

[V8VENOM]

Can anyone verify that IRQ sharing on AMD/VIA based systems has some issues/problems? Under WinXP, I've noticed that on Intel P4 based systems unique IRQs are assigned to each device and rarely is the same IRQ shared. With AMD/VIA systems just the opposite seems to happen, NIC, Video, USB, Sound often share IRQs, sometimes they all share a single IRQ.

The reason I'm asking is that many folks have identified problems with IRQ sharing which are resolved when these IRQs are forced in the BIOS & at OS level to be separate (not shared).

Anyone have detail info on the specifics of IRQ assignment on P4 chipsets & AMD chipset in relationship to WinXP? Is this just a matter of cost cutting design of VIA chipsets?

Rob.

 

[Clarentavious]

AMD doesn't actually make motherboard chipsets (at least not anymore, I think their last was the Irongate 760, which I believe failed miserably - if they do make them, they sure don't sell very many).

You've got to be referring to a VIA chipset supporting AMD processors (Via board with a socket 462 on it)

It won't be related to your OS, Win XP or otherwise, because your OS can't create IRQs past your hardware's limit.

I have in fact encountered this problem with my VIA 266A board by Abit. I don't know why Abit bothered to include 6 PCI slots, because if you filled all of those, your PC proly wouldn't boot (you'd proly get an Interrupt ReQuest or resource exclusion at post).

I've noticed when looking at the INTs (the 4 that there are), there are already some spaces filled. There are 3 for serial bus controllers; but I can't pinpoint what this is referring to. I don't think it is all USB, but of the COM 1 and 2 ports, and I don't think there are 3 USB controllers. I wonder if they are necessary system parts, or optional parts.

What has become more of a problem for my board is, a single piece of hardware that has more than 1 IRQ. My Creative Sound Blaster Live for example, has a built in port for game control pads/joysticks. So there is an IRQ for the audio chip controller itself, then the additional one for the gameport (though I have disabled the gameport for this very reason, to prevent it from tieing up system resources) - not to mention the Multimedia interface, and the SB16 Emulation (sound mode for DOS by Creative Labs, which does use some resources).

So my sound card has more than 1 IRQ, but my D-Link NIC for example only had 1. Even if I put hardware with only 1 IRQ into each of the 6 PCI slots, I still think I wouldn't be able to post.

So yes VIA does seem to have a problem with this, though I can't say Intel is any better.

I'm hoping my new SiS board will fair out better. Maybe the vendors just need to limit the number of PCI slots to avoid this problem. Not to mention other expansion devices that aren't connected though PCI slots.


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Benchmarks don't lie

 

[lhgpoobaa]

Personally i havn't had many problems, in 3 boards the only problem i had was the modem not liking com3 for some reason.

In general, the first PCI slot should be avoided cauz it shares its IRQ with the graphics card, at least on Via boards. 4/5 also shares on certain chipsets.

Running windows 2000 with APCI enabled means that many devices share IRQ's anyway.. ive got about 5 sharing IRQ 11 with no problems.

<b>The Intel Celleron 2.1 & 2.2Ghz processors provide consumers with a great way to get on the Internet. Which one of the 478 pins plug into the phone socket? - <i>Intel & The Inquirer</i></b>

 

[Clarentavious]

Yes, but sharing IRQs generally isn't a good idea (if it can be avoided anyhow). The same is the case with my board and the first PCI slot. You'll probably not want to put anything close to your AGP card anyhow, so it can get more ventilation (if there is some sort of circuit board right below, the fan on the heatsink might not be able to pull air out as well, plus you'll be having it more crowded and heat more closer to it)

On 266A PCI slot 4 also shares IRQs with USB (if you have assign IRQ for USB enabled anyhow). Though what I am saying is, I'm not sure Intel has allowed for any more maximum number of IRQs. My parents have a Pentium 2 board (with like 3 or 4 PCI, and 2 ISA slots on it), and their NIC would only fit in ONE slot correctly without getting an IRQ conflict with the vid card in their AGP.


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Benchmarks don't lie

 

[lhgpoobaa]

heheh yes true.
I dont use my first or second PCI slots for that reason... Infact i CANNOT use the first or second pci slot cauz i glued on a monster heatsink onto my geforce2pro! hehehe
It now runs fanless.

<b>The Intel Celleron 2.1 & 2.2Ghz processors provide consumers with a great way to get on the Internet. Which one of the 478 pins plug into the phone socket? - <i>Intel & The Inquirer</i></b>

 

[V8VENOM]

The OS is not completely irrelevant and can and does reassign IRQs if permitted by the BIOS -- hence ACPI.

What I have noticed is that Intel P4 chipsets seem to work more intelligently with the OS when it comes to assignment of IRQs, it seems fewer are shared. With Via chipsets for AMD CPUs, the opposite seems true, assigning them ALL to a single IRQ in many cases. In some AMD/VIA system this is OK, in others it presents some minor issues such as frame freeze, frame skip, pauses when playing games (especially Force Feed back games using USB devices).

Also, I thought IRQs below 15 (or is that 9) are NOT 32 bit? Is this still correct?

Does anyone have the real details on how a chipset actually shares an IRQ with devices and communicates with the CPU?

 

[V8VENOM]

Found some scraps of info in the follow Microsoft articles

http://support.microsoft.com/default.aspx?scid=kb;en-us;314068

http://support.microsoft.com/default.aspx?scid=kb;EN-US;299340