I have been trying to use an internal clock net in my offset constraint, sourced from a DCM instance. This appears to be legal, according to the CGD: "OFFSET is used only for padrelated signals, and cannot be used to extend the arrival time specification method to the internal signals in a design. A clock that comes from an internal signal is one generated from a synch element, like a FF. A clock that comes from a PAD and goes through a DLL, DCM, clock buffer, or combinatorial logic is supported."
But, this doesn't work for me. If I use the original clock pad in the constraint it works. However, these OFFSETS are driven by a DCM FX output, so the timing is different from the original. Will ISE infer this timing difference? It appears to be unclear to me...
Thanks,
-Brandon