I'm not sure what data pokesav expects, but the name suggests that it wants the EEPROM/SRAM/Flash "backup" data, rather than system RAM.
AR can save and restore the backup data stored on NDS cards. This is probably what you want -- and it's the easiest way to get at that data at the consumer level. (In contrast, I've created my own hardware and control-software that can do the same thing, but that's beyond the capabilities of most people.)
So give AR a try, maybe? "AR DSi" *cough*
can copy the data to/from a microSD.