The RS Decoder v6.0 GUI with ISE 9.1i can report a processing delay that is one less than it should be. This happens in certain cases when the number of clocks per symbol is greater than 1 AND the number of channels equals 1.
The RS Decoder v6.0 GUI will be updated with the future release of IP Update for ISE 9.1i. If the case is number of clocks per symbol is greater than 1 AND the number of channels equals 1, then add +1 to the processing delay.
Please see (Xilinx Answer 30176) for a detailed list of LogiCORE Reed Solomon Decoder Release Notes and Known Issues.