This problem affects DDR, DDR2, and DDR3 products with ALTMEMPHY.
The driver for the example designs for the DDR, DDR2, and DDR3 controllers with ALTMEMPHY contains a design limitation.
If you change the
to a value other than default value of 2, the example driver might
not behave properly. The resulting improper behavior would affect
the design in both simulation and hardware.