Is there any documentation available on creating a dynamic voltage frequency scaling tool in C? I've been unable to find anything on Google and the only applications I seem to be able to find using DVFS are closed source. My preference would be for a Windows based system as that is what I'll be using it on.

Those functions are exposed by the chipset you are trying to control in this way. Not sure how or if the Operating system would get in the way of sending those OP codes to those target devices without writing a driver that bypasses those restrictions or using an existing one. I am also not aware of any standard assembly keywords or interrupts that have standardized that function among various platforms.

I would be interested to know if anyone knows more about this topic. You may want to ask the assembly forum since this is a subject at a lower level than C, although I'm sure its easy to create a wrapper C function once you know the interface.

I would also suggest looking up the datasheet to the main chipset processor that deals with motherboard control systems on your target computer to see what functions are available and what interrupts control that specific function. Then you'd have to tell the CPU to issue those commands to the chipset.