ipcore simultae in modelsim

hi,
there are ddr 、dma and other self_written master ip in sopc ，i want to know how can i simulte the system in modelsim . if i need to write testbench for singal ip or for the whole , right now i load some ip library in modelsim，and simulate some modules include simple ip core ,such as fifo ,ram . but i don't know how to simulate ip like ddr and dma which is the important part of the system

thanks for any help!!!