TXOUTCLK from GTX is connected to the input of the MMCM. The MMCM and GTX of lane 0 which sources the clock to the MMCM must be in the same clocking region. The error occurs if the user attempts to move the MMCM out of the same region as GTX lane 0. A BUFG cannot be inserted on this path due to the requirements of the GTX delay aligner work-around; for details, see
(Xilinx Answer 39456). Starting with the cores released in ISE 13.1 (v2.3 (AXI) and v1.7 (legacy TRN)), the UCF contains placement constraints for the MMCM.
The error message means that the MMCM is in the same clock region as the lane 0 GTX is occupied.
Revision History:02/24/2011 - Initial release