Only one OCL device used and detected
I just ran into an issue with my R9 270 and my HD 6870. After I had to mess around with the drivers to get OpenCL working on the HD 6870, I started xmrig and saw that the HD 6870 was detected as OCL device but the R9 270 was not. After i checked the GPU utilisation of both cards, I recognized that the R9 270 was fully utilized but the HD 6870 was at idle. So the card that has been detected is not working, but that one that hasn't been detected is working...

Hopefully someone can help me with my problem.

I'm also uploading some screenshots, if that could help solving my problem.
![r9 270](https://user-images.githubusercontent.com/11699397/32631461-a6b1e5d6-c5a0-11e7-9751-985339da76e9.PNG)
![xmrig](https://user-images.githubusercontent.com/11699397/32631462-a6d31260-c5a0-11e7-936b-5f546d0bcb7e.PNG)
![6870](https://user-images.githubusercontent.com/11699397/32631463-a6f11bac-c5a0-11e7-86b3-90fda6af130e.PNG)
![config](https://user-images.githubusercontent.com/11699397/32631704-51cb4a2a-c5a1-11e7-90b6-a0c89929e664.PNG)
