Hi Jez! I was the one that I was interested in SDR SDRAM interfacing to 8051. I had posted a message in my old post where I was writing that I found some free VHDL code for implementing an SDR SDRAM controller from Altera, Xilinx and Lattice. Of course necessary changes have to be made to these codes to interface it with an 8051, like the ones you made to Xilinx's VHDL design. Also recently I found another free VHDL design for implementing an SDR SDRAM controller. Anyone interested can visit this site: http://www.cmosexod.com/
You can make some changes to all the above VHDL codes to implement even a DDR SDRAM controller.