We copied the ICE core design but had difficulty getting the upper 128MB of DDR2 working without "aliasing" back on the lower 128MB. The issue was actually a GEL file configuration problem, since it was set for 75 ohm and the ICE is 50 ohm (or less) termination. The following line in the GEL file needs to be changed:
#define DDR2_SDRAM_CONFIG 0x43805332 //termination = 1 (50ohm)
// original GEL file below
//#define DDR2_SDRAM_CONFIG 0x41805332 //termination = 1 (75ohm)