I have a successfully routed Vivado 2015.2 design. However when the design is migrated to Vivado 2015.3, it has the following routing errors:
Why is this happening?
In the error message above, a change in opt_design causes the routing issue. opt_design is moving a IBUFDS_GTE2 -> BUFG -> LUT connection to a IBUFDS_GTE2 -> LUT connection.
This change causes a new BUFHCE global clock resource to be used, but not counted as the IBUFDS_GTE2 -> LUT connection is not a global clock.
This fails routing instead of failing in place_design.
To work around this issue, the following parameter can be set:
Alternatively, a DONT_TOUCH constraint can be used on the affected nets.
This issue has been resolved for the 2016.1 version of Vivado.