DDR for Spartan 3

Hi

I would like to design a DDR controller for a Spartan 3. I have trie using MIG 1.5 but without much success. It claims to work with all Sparta

3 devices, yet I have found it to be unreliable and not generate design with all Spartan 3 devices. Can I ask how others go about with DDR. Do yo design your own cores, buy a 3rd part core or use Xilin cores?

Thanks

Jon