When using the LogiCORE Ethernet 1000BASE-X PCS/PMA or SGMII Core in Virtex-4, a DCM is instantiated in the top-level wrapper file to meet the GMII input timing. How do the new Virtex-4 timing parameters affect these DCM? Is the DCM_STANDBY macro required?
Refer to (Xilinx Answer 21605) for details on how different Virtex-4 stepping levels affect your design when targeting Virtex-4 devices.
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 (Xilinx Answer 21127) for more information on how to use the macro.