hi,

Dual Port RAM is not DMA replacement. This RAM may be useful when you need data exchange buffer or something like it.
DMA is designed for another purposes: this hardware technique allows processor (or other hardware) to continue its work while Direct Memory Access module does perform copy, move, modify or exchange data over memory areas.
For example, one our comercial project has MCU, DataFlash, CPLD, temporal RAM and Video RAM. After power up, MCU unpacks work data from Flash into temporal RAM. It uses MOVXes for it.
Now CPLD contains SVGA refresh video engine which works with video RAM. Time to time MCU needs to display some data on monitor. If it would copy data from temp. RAM into Video RAM with just read-write by MOVXes then it losts productivity totally. Let say that for 800x600 resolution full screen copy may take some seconds. Instead it, MCU utilizes DMA engine programmed inside CPLD. By this way, MCU writes to DMA registers: start addresses of source and destination memories, the size of memory to be copied and sets "Do it!" bit finally. DMA engine shares read and write memory cycles with refresh engine and does full screen copy for some milliseconds and then generates MCU interrupt by which it reports about that task has been done. All this time MCU continues to do its main work instead thousands of movx,movx,movx...
This is example where I do not see how Dual Port RAM may help in place of DMA.

Regards,
Oleg