The PCI Core description instructs users not to use a CLKDLL with the Virtex PCI Core. Why?
The DLL would violate the PCI specification for two reasons:
1. The PCI specification state that the clock can vary from 0 to 33 MHz. The DLL would loose lock in this case.
2. The DLL makes the clock to output delay slightly too fast for the PCI spec.
If you are using PCI in an embedded system in which the clock frequency can be kept constant, the DLL can be used.