Found this usefull app note (TN-29-06) which is a controller for a Micron NAND flash which presents a standard sram interface to the procesor and generates the control signals for flash memory,as it is the sram interface is 16 bit but its wouldn't be hard to change it to a standard 8052 interface,as for the xilinx spartanIII device most of that appears to be taken with two 2k byte buffers which could be cut down as required to fit into smaller and cheaper devices.

http://www.micron.com/products/...hnote.html