I understand that the OpenCL compiler first places and routes the design with an unrestricted fmax and then, based on the timing report, chooses the maximum possible fmax for the design and reroutes it with that value used as timing constraint. Even thought this process ensures that the design will run at its maximum frequency, it prevents user control over the operating frequency and creates a lot of trouble when benchmarking small changes in a fixed kernel since the user will also have to take the effect of the variable fmax into account which is not necessarily linear.
Is there a [hidden] compiler switch to force the OpenCL compiler to place and route the design at a fixed operating frequency, or is there a way to manually redo the last rerouting step with a user defined operating frequency in an OpenCL design?
P.S. I already know the --fmax switch but that only changes the target fmax which controls the number of registers the compiler inserts into the pipeline; it does not allow the user to fix the operating frequency.