why don't you leave the fan at default speed? I will try to work something out for the next release.
do you see the fan rpm reported in other programs for the x770? I think it does not read out fan speeds or the drivers do not tell the program that is why it bails out.
I really don't need to change the fan speed since I'm generally running at 100% all the time (one card runs at 50% though since it is well ventilated). However, being able to collect the fan speed will allow me to write a script that will let me auto-tweek the speed based on temperature, if needed.
Currently, I am using MSI Afterburner to monitor fan speed. This program, along with the ATI Catalyst program both report the speed as a percentage so there must be some API in place to retrieve this data; maybe I can pop a question to the RivaTuner author and ask which API he uses for this purpose. Since I am not using the ATI program actively, my default fan control is in fact whatever MSI Afterburner chooses to do.
My goal is to ultimately use your tool without relying on MSI Afterburner to monitor and report fan speeds (if possible).