Here is what happens if you have hardware crossfirex enabled

[smc13]

I decided to try crossfire since I now have two hd4850 video cards. I got a crossfire interconnect bridge from a friend, I put the 2nd card into pci-2, connect the two cards with a bridge, and boot into windows. It works fine. Now for the fun test of trying it under OSX. I boot up, it goes to the boot screen then it give me a light blue screen for a long time before presenting me with the login screen. Once I am at the login screen, it works just like it would with one card, but it has one heck of a delay before the login screen. The issue is the card in pci-2. The OS doesn't seem to know what to do with it. Here a snippet from the kernel.log:

 

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: ** Device in slot: SLOT-2 **

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: ** GPU Debug Info Start **

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00009442

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x000000cb

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000001

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000018

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x0000fbce

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000001

Mar 13 09:58:56: --- last message repeated 1 time ---

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00009442

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000001

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000015

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000000

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000001

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000047

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000000

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000001

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000058

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000012

Mar 13 09:58:55 Steve-Cohens-Mac-Pro kernel[0]: 0x00000001

 

This repeats several times for a few minutes:

 

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0xb27d21b9

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0x89dbfa33

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0xfb8daad6

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0x21577b94

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0x2a7dcd1e

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0xcbddeff1

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0x58aaeaf3

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0x33d3258b

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0x8b29a154

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0xa1298630

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0xd1a208da

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0xaaf4c3c3

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0x30902d54

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: 0x86d91185

Mar 13 10:00:45 Steve-Cohens-Mac-Pro kernel[0]: ** GPU Debug Info End **

 

Almost two minutes of waiting before continuing, but the operating system does work.

 

Also, both video cards show up in system profiler, though the one in slot-2 isn't usable. I plugged a second monitor into it and no picture. oh well.