Where to initialize DDR3?

What is the recommended place to initialize DDR3 memory? As far as I understood, DDR3 initialization could be done in boot table format by supplying an appropriate table whereas DDR3 initialization is actually done by the EVM's IBL. Is there also a way to accomodate DDR3 initialization in a ROMFS image? If a specific application is to be loaded to DDR3 memory and the application wants to use DDR3 settings different from those in IBL, how would one do that? I can imagine that running DDR3 at reduced speed could decrease power consumption. regards Guenter