I got a really strange experience

now, I have one more question.

if I want to use the niosII soft IP core, I should download the .sof file to the DE2 board, then the hardware of the system has been setup. And then, I run the niosII IDE to run software on the hardware which has been setup. It is right that I store the software on the FPGAs internal block RAM, but when I redownload the .sof file, the RAM in the FPGA should be cleared up. I definitely understand if I want to change the result of the program, I should clear the RAM of the system, but why I have to regenerate the .sof file which is stored in my PC not in FPGA.

thanks

--- Quote Start ---

The initial contents of the FPGAs internal block RAM is stored in the .sof file. If your NIOS code is being stored in internal block RAM, then your compiled code will be part of the .sof file. If you change your C code, you will then obviously need to also regenerate the .sof file.

Using the "Update Memory Initialization File" option on the Quartus "Processing" menu can be a short cut to recompiling the entire Quartus project.

While developing, you can also download updated NIOS code using JTAG to save having to generate a new .sof file every time. For example, from the Nios II Command Shell you can do "nios2-download -g filename.elf". Once you are happy with the results, you can then generate a new .sof file to make the changes more permanent.

--- Quote End ---