Problem with Pixel_Buffer_DMA and SDRAM

The reset vector is where the first instruction is read from.

If it references SDRAM something would have to initialise the SDRAM before the processor can execute the code from it.

(This is almost certainly possible if you hold the cpu in soft-reset while something else writes the code into SDRAM.)

Most of the boot sequences actually use the nios cpu (running from some internal memory) to write the code and data into the required memory areas.