For MIG v3.2 Virtex-6 DDR3 component-based designs using on-die termination (ODT), MIG does not select the correct ODT values.
In a component design, Rtt_nom should be set to the appropriate value (40, 60, or 120 ohms) based on the user system requirements (e.g. based on signal integrity simulation), and dynamic ODT (Rtt_WR) should be disabled. However, for a component design, the MIG GUI only gives the user the option of setting Rtt_WR, and automatically disables Rtt_nom. Disabling Rtt_nom will cause ODT to be disabled during write-leveling - adversely affecting the signal integrity of the DQS nets and potentially affecting the accuracy or completion of write-leveling.
To work around this issue, modify the following parameters at the topmost level of the MIG hierarchy to the following values:
RTT_NOM = "40", "60", or "120" (depending on system requirements)
RTT_WR = "OFF"