Error CMP409: DDR instance <DDR_instance_name> has fanout more than 1. It cannot be combined with the IO instance <instance_name>.

The DDR_OUT core is intended to be paired with a regular output I/O core, so as to use the built-in output DDR I/O function. The net connecting the DDR_OUT core to the regular output I/O macro must have a fanout of 1.

Action

Make sure to connect this DDR_OUT core to only one regular output I/O macro.