BUFGCTRL – Internal Global Clock Buffer
Any BUFGCTRL can drive any DCM in the Virtex-4 device using dedicated global
routing. A BUFGCTRL can drive the DCM CLKIN pin when used to connect two
DCMs in series.
我也没有这样用过,不过你看这段话对你有帮助没?第一个DCM的输出是不是不满足第二个DCM输入的条件?