About DMA problem..please help me

There could still be a cache problem, because with your memcpy statement, you are using the cached address, and as a result the NIOS CPU may not immediately write the cache contents to the buffer area. After that you read and display the uncached values, so they could be different than what was written by memcpy.

I wouldn't recommend to keep the memset with DEPTH*2. You are writing on the stack in a space that was probably allocated for something else, and it could trigger all kind of unexplainable bugs in your code.