The bit-reversal SDRAM address mapping

Abstract

The performance contributions of SDRAM address mapping techniques in the main memory of an embedded system are studied and examined. While spatial locality existing in the access stream increases SDRAM row hit rate, it also increases row conflicts. Mapping of the physical address bits into SDRAM column, row, bank and rank index impacts system performance significantly. A novel address mapping scheme, called bit-reversal, is described and experimentally compared against known methods. The bit-reversal address mapping increases SDRAM row hit rate from 43% to 66% by distributing conflicting memory accesses over independent SDRAM banks. Bit-reversal address mapping reduces the average memory access latency by 26%-29% over other methods, resulting in a 11.7%-13.5% reduction of total execution time. The configuration space of bit-reversal address mapping is explored. Finally, limited studies examining the impact of address mapping techniques in conjunction with SDRAM controller policy and virtual paging illustrate that mapping is better suited to virtual memory free embedded systems than desktop workstations incorporating paging mechanisms.