DDR SDRA IP local address

The number of address bits are determined by this formula:

log2 ([SDRAM address span * 8] / [SDRAM local data width])

For a given memory device the address span is fixed so if you wanted more or less address bits you need either wider or more narrow memory. Assuming you are mastering this memory with a 64-bit data path then you would just wire the word addresses from the memory master to the SDRAM controller. You may have the last 27th address bit floating but that just means you are not using up the entire addressable memory of your master.