I have found some strange behavior of DDRSDRAM-controler.
when power up my system, the core does not work good. but, once I put reset signal in the SOPC builder. it works well. I thought this is matter of time. so, I made counter which count till 1sec ( I tried 10 sec as well ). and make reset signal. but the reset does not work. no matter how long it waits. then I put reset signal externally, it works again. what happens in the SDRAM?