Ok, go I have 3x Gigabyte 280X, decent Asus mobo that can deliver enough power to all three cards and the usual crap system just to make it work (Celeron, couple GB RAM, small HDD). I have an issue where one of the cards (randomly picks between the three) will either not start hashing at all, or at a very low rate (like 2-3Kh/s). The other two cards run just fine and dandy.
If I quit and restart cgminer (tried both 3.7.2 and 3.6.6) multiple times, sometimes 50 restarts, finally all three cards will work properly. Normally the AMD display driver will crash and restart about every other restart of miner as well. If I leave it running with just two cards hashing, cgminer will normally crash after a minute or two.
Sometimes I noticed it will work if I have Trixx open, sometimes if I have it closed so I don't think that is making a difference. It's clearly an AMD driver issue. I just moved up to the newest version of Catalyst (13.12) with the latest driver (126.96.36.199) and it has made no difference.
My config as follows:
-i 13, vectors 2, worksize 256, lookup-gap 2, thread concurrency 8192, shaders 2048, gpu-engine 1034, gpu-memclock 1500, powertune 20, gpu-threads 2
These settings work just fine, and then I use Trixx to adjust voltage to 0.999 (it works - gets me over 720Kh/s when it works right). I can't for the life of me figure out why one randomly selected card will fail to start properly each time I start cgminer. Any clues?