The following timespec definition is not understood by Constraints Editor:
timespec ts05 = from pads(pclk) to ffs = 6 ns;
The following warning is generated:
WARNING: Unable to create FROM TO with ts05.
The warning can either be ignored, or you can modify the UCF file to include the timegrp, and then the timespec.
timegrp pad_pclk = pads(pclk);
timespec ts05 = from pad_pclk to ffs = 6ns;
This is fixed in the 4.1i software release.