ISE10.1警告

ERROR:Place:1018 - A clock IOB / clock component pair have been found that are not placed at an optimal clock IOB /
   clock site pair. The clock component <start_IBUF_BUFG> is placed at site <BUFGMUX_X1Y1>. The IO component <start> is
   placed at site <L6>.  This will not allow the use of the fast path between the IO and the Clock buffer. If this sub
   optimal condition is acceptable for this design, you may use the CLOCK_DEDICATED_ROUTE constraint in the .ucf file to
   demote this message to a WARNING and allow your design to continue. However, the use of this override is highly
   discouraged as it may lead to very poor timing results. It is recommended that this error condition be corrected in
   the design. A list of all the COMP.PINs used in this clock placement rule is listed below. These examples can be used
   directly in the .ucf file to override this clock rule.
   < NET "start" CLOCK_DEDICATED_ROUTE = FALSE; >