I need some help of creating shared ddr sdram memory

Ummmmm I forget.... I haven't done this stuff since school but you can take a look at this to see if it gives you any ideas: http://www.altera.com/support/examples/nios2/exm-multi-nios2-hardware.html?gsa_pos=4&wt.oss_r=1&wt.oss=multi That design shares data between two CPUs using a Mutex and on-chip RAM

If I remember correctly the mailbox was essentially two mutexes, a 'binding' to some physical memory in your system, and some software protocol implemented in the driver for the component. Maybe looking at the driver will give you some ideas of what to do while you eliminate anything you don't need that might slow it down.