R9 280X crossfire in 2006 Mac Pro?

[chackett]

I've gotten an MSI R9 280X flashed (thanks Mr. Zarniwoop and everyone over at Netkas) and running like a champ in my 2006 Mac Pro. It's working so well that I decided to try to set up a crossfire setup (for gaming in Windows). I have a second MSI R9 280X, and bought a Seasonic 600W external PSU to power the cards. Both of the cards work great individually, but as soon as I hook them together and try to enable crossfire - instant BSOD. I've tried the latest Omega drivers, the most recent beta drivers, the Boot Camp drivers from early last year - none of them work.

Has anyone been able to get this to work? I (somehow) managed at one point, and it was working great; almost a 60% improvement in framerate; but I had flashed the first card but not the 2nd, and connecting them messed up the display on "About This Mac" somehow. I decided to get clever and flash the 2nd card too, and ever since then I haven't been able to get crossfire going again. Frustrating. I should have just left well enough alone.

 

[MacVidCards]

If they have the switch, put them both in PC mode.

 

[chackett]

If they have the switch, put them both in PC mode.

Yeah, they do; I'll give that a shot. Should that be done before I reboot into Windows? Or afterwards? And same question about going back the other direction - can I boot into Yosemite with both switches on the UEFI position, or should I change them back to the legacy (flashed) side before I reboot?

 

[h9826790]

Switch them before you boot, once bootup, the switch basically doing nothing.

E.g. If you are in OSX now, you can switch it to UEFI mode when the card still running, and then reboot the machine into Windows.

 

[chackett]

If they have the switch, put them both in PC mode.

Holy cow, thanks for the tip! What a difference! Everything worked just as it was supposed to - installed both cards and the crossfire bridge, booted into Windows 7, installed the Omega drivers, and Crossfire was automatically enabled.

Tried booting into Windows with the switches set back to legacy, and instant BSOD (no surprise to someone who knows what they're doing, probably). But having to use the System Preferences/Control Panel to switch operating systems is a small price to pay. I can always flip to legacy if catastrophe strikes and I need the boot manager for some reason.

Thanks again for your help.

 

[MacVidCards]

To clarify, legacy would typically mean the BIOS only position. Most of the cards ship for PC with one EEPROM loaded with just BIOS and the other liaded with UEFI & BIOS hybrid used by UEFI PCs.

Since Mac EFI is a UGA offshoot the GOP UEFI is basically invisible, in which case it just loads the PC BIOS. When you run the Mac EFI side you gain bootscreens and proper name for card, and ability to see "PCI" section of system profiler. Sadly you frequently lose ability to Crossfire in Windows too.

So what is on other side of switch from Mac EFI can be either the regular PC BIOS or the UEFI BIOS Hybrid, all that is important is that there is no Mac EFI, for whatever reason it breaks Crossfire.

And before I get a storm of questions, this only applies to AMD Tahiti cards, as far as I know. NVIDIA cards use SLI and presence of EFI isn't a problem, getting past NVIDIA board check is.

 

[Jasper6120]

I just want to ask something, because I have a R9 280x in my mac and it is running very slowly. I have not hooked it up to an external power supply. Do I need to do that in order to give it the wattage it needs to run efficiently? (sorry for the hijack, I just can't seem to find an answer anywhere and figured you'd know)

 

[chackett]

I was initially running mine without an external power supply and it seemed fine. I was getting benchmarks much like those reported in the following thread: https://forums.macrumors.com/thread...-boot-screens-pci-system-information.1808938/

Somewhat slower than maximal speed because it's PCI 1.0 (and running OS X) but I was happy with the performance. Especially in Windows. There is a danger that you may end up drawing more power than your motherboard can safely handle (although I never had any problems), but I haven't heard anyone complain about speed. I can't rule out that there's something special about the software you're having trouble with, though. Try running the Unigene benchmarks and see what you get.

I did add an external supply, but I had no choice since I've set up two cards for Crossfire in windows. No way to power both of those without an external supply. I could re-run the Unigene benchmarks but I bet I won't see any difference.

 

[Jasper6120]

Hi yes I ran Unigene Heaven on the highest settings and it is hovering around the 20fps mark. I don't know. My GTX 660ti got way higher. Its a head scratcher. I'm just starting to think that the card is malfunctioning :/