ATI CrossFire instability and horizontal bands?

Question

I recently added another ATI 5870 card to my system to experiment with ATI Crossfire (dual GPU) performance increases.

However, I've had a lot of intermittent stability problems, most seriously a set of oscillating horizontal bands which appear during gameplay and become quite severe, to the point that you can barely see the screen to exit the game!

It looks a little like this:

My system has an overclocked Sandy Bridge CPU that has been rock stable with a single 5870, but adding the second video card and enabling CrossFire seems to be problematic. The cards are both installed fine, fully seated with plenty of space between them, have both PCI 6-pin power connectors connected, and my 850 W power supply should be ample.

The Catalyst hardware properties look fine:

Primary Adapter     
Graphics Card Manufacturer  Powered by AMD  
Graphics Chipset    ATI Radeon HD 5800 Series   
Device ID   6898    
Vendor  1002    

Subsystem ID    2289    
Subsystem Vendor ID 1787    

Graphics Bus Capability PCI Express 2.0 
Maximum Bus Setting PCI Express 2.0 x8  

BIOS Version    012.018.000.001 
BIOS Part Number    113-C00801-XXX  
BIOS Date   2010/02/08  

Memory Size 1024 MB 
Memory Type GDDR5   

Core Clock in MHz   875 MHz 
Memory Clock in MHz 1225 MHz    
Total Memory Bandwidth in GByte/s   156.8 GByte/s   

Linked Adapter      
Graphics Card Manufacturer  Powered by AMD  
Graphics Chipset    ATI Radeon HD 5800 Series   
Device ID   6898    
Vendor  1002    

Subsystem ID    2289    
Subsystem Vendor ID 1787    

Graphics Bus Capability PCI Express 2.0 
Maximum Bus Setting PCI Express 2.0 x8  

BIOS Version    012.020.000.001 
BIOS Part Number    113-C00801-100  
BIOS Date   2010/03/31  

Memory Size 1024 MB 
Memory Type GDDR5   

Core Clock in MHz   850 MHz 
Memory Clock in MHz 1200 MHz    
Total Memory Bandwidth in GByte/s   153.6 GByte/s

I've tried the following:

• swapping the primary (ever so slightly faster at 850 MHz vs 875 MHz) and secondary cards, so now the primary is the slower not faster one.

• doing a clean driver remove with Driver Sweeper

• installing the latest beta ATI Catalyst drivers

• installing the latest CrossFire application profiles

All to no avail!

Answer 1

This was a tough one.

After many hours of trial and error, someone mentioned to me that overclocking could be the issue:

overclocking can create issues with dual card setups (both CrossFireX and SLI.) You have to be careful about PCIe timings.

I thought overclocking couldn't possibly be it, since this system has been ultra stable for MONTHS with the current settings.

But setting BCLK to 100 (default) from the "auto extreme overclocker" override of 103 and not overclocking does seem to have worked. I was able to play several BF2:BC rounds with no issues, though I did see a hint of the horizontal banding at one point, it went away by itself.

So, watch out for any PCI Express overclocks when running an ATI CrossFire video card setup!

edit: additionally, I was seeing some other .. oddities .. that were resolved by setting the two video cards to the exact same clock and memory timings in the Catalyst Control Center AMD Overdrive section (although they are both 5780 cards, obviously, they came from the manufacturer with slightly different clock and memory timings). Thus, I also strongly recommend making sure both cards in Crossfire have the same settings.