Selecting a single device/platform

[hashish]

I've got Device #1 and Device #2 on platform #1.

Wishing only to use device #2 for an attack.

appending the following hasn't worked:

-d 2
-D 1 -d 2
-d 1,2
-d 2,1

Does anyone know the correct command to only use the second GPU?

Thanks