Virtex6的MMCM问题

在用Virtex6的MMCM时，到MAP的时候就会提示如下错误：
"physical_group_UUT/CLKOUT1/UUT/MMCM_BASE_inst"' has its target frequency,
   FVCO, out of range. Valid FVCO range for speed grade "-1" is 600MHz -
   1200MHz. The computed FCVO is a function of the input frequency
   CLKIN1_PERIOD, the division factor divCLK_divIDE, and the CLKFBOUT_MULT_F
   attribute (FVCO = 1000*CLKFBOUT_MULT_F/(CLKIN1_PERIOD*divCLK_divIDE)). The
   CLKIN_PERIOD attribute may have been set by ngdbuild based on the user
   specified PERIOD constraint. The current calculated FVCO is INFINITE because
   CLKIN1_PERIOD is 0. To resolve this error, either the attribute should be
   changed to a non-zero value, or CLKIN1 input should be disconnected.
   Reference the V6 architecture Users Guide or search the Xilinx Answer Records
   database for the error code.

可是我CLKIN1_PERIOD不是设的0啊，哪位大哥指点一下哈输入时钟是50MHZ,我用COREGEN和language template都提示同样的错误啊

如果是coregen生成的时钟模块，一般不可能有问题（我没有遇到过），如果是自己直接配置的，需要检查下多个时钟输出是否是可行的，检查各属性设置是否正确。
貌似频率低于10M也是不行的。

VCO的输出是由频率限制的，太低了也不行，至少600M，查一下div/MUL的设置。

好的，谢谢各位哈