When using the Gigabit Ethernet MAC Core with the RGMII physical interface, two DCMs are instantiated in the top-level wrapper file. How do the new Virtex-4 timing parameters affect these DCMs? Is the DCM_STANDBY macro required?
For details on how different Virtex-4 stepping levels affect your design when targeting Virtex-4 devices, refer to (Xilinx Answer 21605).
For information on the new Virtex-4 timing parameters, see (Xilinx Answer 21127). Notice that the DCM_STANDBY macro is required to meet the DCM_INPUT_CLOCK_STOP and DCM_RESET requirements. The DCM_STANDBY macro can be manually instantiated or automatically inserted by ISE depending on the stepping level of the device that is being targeted, as indicated in (Xilinx Answer 21605).
If it is determined that manual insertion of the macro is required, refer to (Xilinx Answer 21127) for more information on how to use the macro.