Problem: interfacing DDR2 with Terasic DE-4 CALIBRATION FAILURE

Hi Gennaro, actually, we have never implemented simulation as you tried, thus not so clear about this part temporarily, here my partner advised another attached example, but an actual one for your reference, it can be executed instead. Anyway, hope it's of a little help. May I know your university is? I'm more than pleased to assist in further, free to drop me a line if you think necessary or more convenient, any queries, thanks!