[Place 30-519] REFCLK pin of IDELAYCTRL instance 'u_idelayctrl' is driven by 'u_ibufgds_200'{IBUFDS}. This will lead to unroutable situation. The REFCLK pin of a IDELAYCTRL instance should always be driven by clock buffer

我的差分时钟输入用的是IBUFGDS,为什么会出这种错误啊，求大神指导？