Description

How do I choose between Global Clocking and Regional Clocking?

Solution

Both regional clocking and global clocking with DCM can operate up to 1 Gbps in a Virtex-4 device. Regional 

clocking requires fewer clock resources than global clocking with DCM; however, it places 

an area restriction on the logic that uses the regional clock. See the "Constraining The Core" section of the SPI-4.2 User Guide.