AR# 34219: Virtex-6 MMCM - Cascaded MMCMs may not work in hardware
Virtex-6 MMCM - Cascaded MMCMs may not work in hardware
In the Virtex-6 FPGA,cascaded MMCMs may not work in hardware. The behavior seen is that the second MMCM in the chain does not lock.
The ISEimplementationsoftware automatically selects the COMPENSATION mode for thecascaded MMCM. In some cases, the software does not set this attribute correctly.The workaround to this issue is to manually set theCOMPENSATIONattribute to CASCADE for the second MMCM in the user design. This issue will be fixed in ISE 12.4 software.