This worked for me
I picked up a 5770 cheap yesterday to run along with a 5830. Noticed 100% cpu usage once I started mining. I had 0% usage when running one card. Seems to be a common problem caused by the openCL drivers. Here's what I did to fix it. Running WIN7 64 bit / Phenom II dual core cpu.
I have one monitor installed to both cards (HDMI / VGA port)
Boot with both cards plugged in. Go to screen resolution display settings and on the drop down menu for multiple displays select " Show desktop only on 1" (for 1st installed card)
start up your miner for that card. Go back to display settings and select "show desktop only on 2" (for 2nd card) Now start up another miner for that card.
I am now getting 0% cpu usage. I'm assuming this will work for Windows XP also. You may have to select extend display or detect first for Windows to recognize both cards before doing the above.
Does it have to be a real monitor and/or the same monitor? I tried with 1 real monitor and the other with a dummy plug, 1 attached to each card, and I still get cpu bug. 11.9 release drivers with the sdk that comes with it, guiminr, phoenix 1.6.2, phatk 2.2, -a 250 -k phatk2 VECTORS WORKSIZE=128 FASTLOOP=true AGGRESSION=4 (dont need to specify bfi_int anymore)
I'm using two real monitors.
Edit: I switch both displays on to set the clocks. Then I close off a display and start a miner, then close the other display and start the other miner.
Oh, you're using 2 seperate monitors. I was about to say "I followed this to the letter, still doesnt work", but now I have to hook up TWO monitors... I was using 1 monitor that had both vga and dvi on the back and I just switch it on the monitor... BRB
Edit: Hooked up my dell 30" via dvi to my main gpu 5830, hooked up a 22 inch hanns G on VGA on my 5870 that normally is used just for mining and usually has no monitor on it. Booted computer with both monitors on and had extend displays as it was turned on. I went to screen resolution and picked "show on 1" and started the miner thats respective for the monitor that is currently showing stuff (the other one automatically switches to standby at this point). That miner is always 100% cpu bug on 1 core. While it is mining, I do "show desktop on 2", the main monitor goes on standby, other moni9tor turns on, and I turn on the miner respective to that gpu. It's still 100% cpu bug. I already force both instances to 1 core so it's still using up 1 core.
What drivers are you using? what sdk? What miners? You're using the same os as me so it cant be that, and i dont thin kthe card difference should do anything since you're using 2 diffrent cards as am i.. this is so frustrating. It's not an option to use 2.1 sdk either because for some reason guiminer as well as phatk 2.0/2.1/2.2 won't run with sdk 2.1