Cannot enable CrossfireX on 2* Radeon 4870

[streetster]

Hi Guys,

I just picked up another 4870 for cheap off ebay to pair up with my other 4870 I bought 2 years ago.

Both are Sapphire 512mb flavours, the ebay one has a different cooler and the card layout is slightly different... GPU-Z for the cards is:



left = ebay
right = original

If I fire up CCC it says that the 2nd adaptor (original card) is disabled, though both appear in Device Manager.

I've got Catalyst 10.7 installed (reinstalled a couple of times too), but am losing the will to live as to why it doesnt work.

Motherboard is an Asus P7P55D-E, there is a newer bios available which I'll try tonight, but no mention of crossfire in any of the bios updates, or within the bios menu itself.

I've had a quick google this morning and it seems some people may have issues with crossfire on 10.7 with the 4xxx range of cards (suggestion is to try 10.4), so I'll try an older driver tonight...

But... does anyone have any ideas why it doesnt work? Ie - do they have to have the same bios revision etc? or should it not mind?

[scaryjim]

Noticable thing: the right hand one is running at PCIe x1, not x16 - the left hand one is running at PCIe 2.0 x8. Looks like a PCIe lane issue to me. I'd have a dig round the motherboard BIOS to see if you can find any settings for split up the PCIe lanes evenly.

[DDY]

Do you have any other PCI-E cards installed? Other than the two graphics cards of course.

Maybe the USB3/SATA6G chipset is taking up too many PCI-E lanes, disable the USB3/SATA6G chipset in the BIOS and see if that solves the problem.

[streetster]

I'll have another pootle round the bios this evening, in terms of other pci-e cards - I've got an Abit Airpace wifi card in one of the x1 slots.

What should they be?

[jimbouk]

Ideally x16 and x16, but usually x8 and x8. It's a bit odd that one is PCI-E 2.0 and one not if they're meant to work with crossfire well. I'd see what your manual says about crossfire support.

[streetster]

Seems I cant upload anything here... so, the manual says:

PCI Express 2.0 x16 slots

This motherboard has two PCI Express 2.0 x16 slots that support PCI Express x16 2.0 graphics cards complying with the PCI Express specifications. Refer to the figure below for the location of the slots:

-- PCIe x1_1 slot
-- PCIe 2.0 x16_1 slot (blue, at x16 link)
-- PCIe x1_2 slot
-- PCI slot 1
-- PCIe 2.0 x16_2 (black, at x4 link)
-- PCI slot 2
-- PCIe x1_3 slot

so, obviously the two graphics cards are in the blue and black slots, wifi card is in the top PCIe x1_1 slot, and my soundcard is in the PCI slot 1.

[scaryjim]

OK, the board won't do symmetric crossfire whatever, because the second slot only runs at x4 anyway. But that still doesn't explain why it's negotiating to x1 instead. Have you tried swapping the cards over to see what GPUz says about the PCIe lanes then? According to the manual one should say PCIe 2.0 x16 @ x16, the other should say PCIe 2.0 x16 @ x4. So something is going amiss somewhere...

[Terbinator]

does it not mention anywhere when running in CFX both will drop down too x8 ? x4 is going to be a bottleneck i would of thought.

[streetster]

balls...

The second PCIe x16 slot (black) and the three PCIe x1 slots share the bandwidth from the Intel® PCH. When any of the PCIe x1 slots is occupied, the second PCIe x16 slot will be switched to x1 mode.

from here.

Soooo looks like i'll be reverting to a USB wifi card from tonight. Balls.

[Terbinator]

Must be because the rest of the spare bandwidth is dedicated to the USB3/SATA6 ports.

[streetster]

Hmmm, according to these guys there shouldn't be too much of a loss running at 4x vs 8x or 16x, seeing as that is a 5870 rather than a 4870 too.

I guess I'll find out later!

[scaryjim]

That'd make sense: a couple of PCIe lanes for each of those would leave 4 to share between the PCIe slots. <snip>

Still, odd that the primary GPU only got 8x - very odd indeed... I'd be putting each GPU in that primary slot separately in case there's an issue with the card - should be running at x16 in an x16 slot...

EDIT: ignore that thing about PCIe 1, it's utter rubbish: it provides PCIe 2.0 lanes. Sorry!

[streetster]

Ok, so found an old netgear wireless dongle, faffed about with 64bit drivers (thanks fal1!), removed my pci-e wifi card, fired up the machine and was prompted for crossfireX. woop!

Sooo now gpu-z looks like this;



left=ebay
right=existing card

sooo... it still says PCIE 2.0 x16 @ x8 2.0, and worryingly the other card says PCIE x16@ x4

Ran 3dmark06, got ~23k, disabled crossfire and got ~17k, so seems like it's doing something. Will have a browse of ORB to see if that is a fair result for my rig.

[Pob255]

That board runs one pci-e x16 at x16 when only one graphics card is use
when you use 2 cards the first x16 slots drops to x8 and the 2nd runs at x4
However the 2nd pci-e x16 running at x4 is shareing lanes with the other pci-e x1 slots, what this means is that they are normally turned off if nothing is pluged in, plug in a pci-e x1 card and it turns them on reduceing the pci-e x16 (x4) to a x1 slot.

Why I'd a void the plane or LX asus mother boards and go for the Pro, EVO or Delux versions. which run a full x16 or x8/x8 without shareing the bandwidth with the other pci-e slots