AsRock 970 Fatal1ty Crossfire

dinin70 wrote: [URL=][/URL]Dear community, I'm trying to run Crossfire with two R9 Fury (16 slot each). I cannot succeed... Every game I run provides me with negative scaling. On AMD site, no one can help me... On page 16 of the manual I can see the following table PCIe Slot Configurations Single Graphics Card = lane width pcie2: x16 lane width pcie4: N/A pcie5: N/A Two Graphics Cards in CrossFireX Mode = lane width pcie2: x8 lane width pcie4: x8 lane width pcie5: N/A Does the lane refers to the 2x8 pins for the PSU connection? Does this means the Motherboard is actually preventing me from using properly two Fury in crossfire with 16 lanes each? Or it has nothing to do with it? Thank you in advance. Sincerely, Dinin70 Here are my specs FX8350 8GB Ram Corsair 1600 AsRock 970 fatal1ty 2x Sapphire R9 Fury Nitro OC Trixx Corsair rm1000x Windows 10 64b

Assuming you have the Fatal1ty 970 Performance board.

The mother board itself is not preventing you from running your two video cards in x16 lane mode, it is the limitations of the board's 970 chipset.

The AMD 970 chipset provides 22 PCIe 2.0 electrical lanes to the PCIe slots on a mother board. Yes, twenty two PCIe 2.0 lanes. Far short of the 32 PCIe lanes needed for dual x16 video cards.

No PCIe lanes are provided to the board by the FX series processors.

Of those 22 PCIe 2.0 lanes, four are reserved (by AMD spec) for a PCIe 2.0 x4 electrical slot, that may be x16 physically in length.

Two more of those PCIe 2.0 lanes are allocated to the PCIe 2.0 x1 slots.

That leaves 16 PCIe 2.0 lanes that may be allocated to one PCIe 2.0 x16 physical slot, or split into two PCIe 2.0 x8 lane allocations, to two PCIe 2.0 x16 physical slots.

The board's specification of PCIE2 and PCIE4, both at x8 lane width is correct, when both lanes are in use in two card Crossfire mode.

Only the 990FX chipset can provide enough PCIe 2.0 lanes to supply two PCIe x16 slots with 16 PCIe 2.0 lanes each.

So obviously no, the x8 lanes does not refer to the eight pin power connectors found on video cards.

The best you will get with any 970 chipset board is two PCIe 2.0 x16 slots, at x8 lanes each, plus one more PCIe 2.0 x16 slot, with x4 lanes, sorry to say. That is exactly what your board provides.

The PCIe lane limitation is simply caused by the AMD 970 chipset. Any and all mother boards made by any manufacture using the 970 chipset will have the same number of PCIe 2.0 lanes available for the PCIe slots.

We must be careful when looking at mother boards with multiple PCIe x16 slots. Just because a PCIe slot is x16 in length physically, does not mean it will automatically have 16 PCIe electrical lanes allocated to each one.

Mother boards with two PCIe x16 slots that both have x16 lanes are very rare. Only the AMD 990FX chipset boards will have that, and the Intel X79 and X99 boards, with certain Intel HEDT processors. There are a few boards that use switching chips to multiplex the PCIe lanes between the PCIe x16 slots, but they are expensive and aren't seen often anymore.

The AMD forum was unable to explain this to you? Or was it something else?

You should not be getting negative scaling even at x4 + x4. You would see lower performance (marginally) than another system running at x8 + x8 but certainly not negative scaling. Parsec's description explains how the lane allocation works, x1, x4, x8, x16 etc but when it comes to crossfire x4 + x4 is the minimum requirement.

Edited by Xaltar - 03 Dec 2016 at 5:11pm

@ Xaltar et all

https://community.amd.com/thread/208578

Hello,

So here is what I exactly did:

- uninstall all drivers through the control pannel
- reboot
- reboot in safe mode
- DDU clean and shutdwon
- shutdown
- clear CMOS, take off card 2
- set the RAM to XMP 1.3
- reboot
- update bios to v1.2
- Reboot
- install last drivers, last ones.
- Reboot
- check everything is installed properly (control pannel /
Radeon Settings)
- shutdown
- plug second card
- on startup screen flashes black as it recognizes the second grapic card.


And still:
- negative scaling in Overwatch for about 30 FPS less
- minimal gain (a couple of FPS) on Warhammer Total War.

Maybe I'm only playing poorly optimized for Crossfire...

Very good point Xaltar. I'll try this now