NIOS II IDE overwrites SDRAM

I'm using DE1 on board SDRAM, first I store the .hex file with control panel (after programing fpga with control panel .sof file), in control panel I can write and read SDRAM; after, I program the fpga with my own design .sof file (NIOS with timer,pio,sram, sdram, etc, etc) and load my c program with nios II IDE, but now, like you say me, I think the problem is the data refresh ........ but now the question is: How I can store data (in this case from a external file created in matlab) and use this data last time????. :confused: