Optimizing Data Layout for Racetrack Memory in Embedded Systems

Racetrack memory (RTM), which consists of multiple domain block clusters (DBC) and access ports, is a novel non-volatile memory and has potential as scratchpad memory (SPM) in embedded devices due to its high density and low access latency. However, too many shift operations decrease the performance of RTM and cause un-predictable performance. In this paper, we propose three schemes to optimize the performance of RTM from different aspects, including intra-DBC, inter-DBC, and hybrid SPM with SRAM and RTM. Firstly, a balanced group-based data placement method for the data layout inside one DBC is proposed to reduce shifts. Second, a grouping method for the data allocation among DBCs is proposed. It helps with the shift reduction while using fewer DBCs by using one DBC as multiple DBCs. Finally, we use SRAM to further help the cost reduction, and a cost evaluation metric is proposed to assist the shrinking method which determines the data allocation for hybrid SPM with SRAM and RTM. Experiments show that the proposed schemes can significantly improve the performance of pure RTM and hybrid SPM while using fewer DBCs.