The PowerupCLK option is mentioned in the Software Manuals, yet there is no mention of this feature anywhere else. What does it do?
This option was included in the software when Xilinx was considering adding the "Powerdown" feature to Spartan-II. As this feature was not provided in the final product, no documentation on the options controlling this feature was created. (The option would have controlled the clock used during the re-powering of the device.) Therefore, this option is no longer used.