help: the DDR2 controller works incorrectly

I use the DDR2 SDRAM Controller v9.1(not the high performance) and my memory is MT47H32M16cc-3. The parameters are set as follows:

clock speed 150MHz

Data bus width 16bit local width 32bit

Row 13bit Column 10bit Bank 3bit

CL 5

the DDR2 works correctly when I use the example driver which is generated by IP, but it works incorrectly sometimes when I replace the example driver by my own driver. My driver is very simple, just writes some data into ddr2, then reads back. But I compare the read back data with the write data, sometimes they are different. And I also find if I just write less then six data at once, there will be no errors. When I write more than six data, there will be errors sometimes. The attached files contain the SignalTap file and my own driver file. Does anyone can tell me where I am wrong?

Thanks a lot.