I am too trying to get a DDR controller up and running on a Spartan 3 and
have found MIG to be very frustrating. At the moment I am looking at the
DDR controller on opencores and have got it simulating under modelsim. Not
sure how easy it will be to get going on real hardware though. I have
posted a few messages on here regarding DDR and havent really got any
replies so either people are having trouble getting it working or are
keeping quiet

Jon

I am having a difficulty grasping project structure, generated by Xilinx
MIG007 software.
I?ve generated 16-bit data DDR1 SDRAM interface to Spartan3 xc3s500-4-efg208
device.
MIG user manual describes user signal interface and timing for ddr1_top
which is the main DDR SDRAM controller. But it?s hierarchically below
ddr1_test and mem_interface_top modules. These probably enhance user
interface or could be used for controller testing, I just can?t find any
documentation regarding their use. 
MIG007 also generated startup_spartan3 module, but here again no information
on how to use it.
I?d like to have a simple SRAM like user interface. If someone?s done this,
I would appreciate some pointers.