Research On The Simulation And Application Of Phase Change Memory

As the scalability of DRAM is reaching the limitation,DRAM cannot meet the high performance computers' requirement for large capacity memory.Phase Change Memory(PCM)is a kind of emerging non-volatile memories and is a potential alternative for DRAM.PCM has the advantage of better scalability,lower idle power and non-volatile data than DRAM.However,there are obstacles that restrict wide adoption of PCM as main memory,such as long latency,limited write endurance,and high write power.Wear-leveling and error correction are two useful methods to extend the lifetime of PCM.However,there is a lack of mature PCM device for research on lifetime of PCM.Simulating PCM with Software is useful method for such research.This thesis is focused on simulation and lifetime of PCM.The main contributions are as follows:We design a memory trace-driven simulator for simulating both wear-leveling and error correction of PCM.LPCMsim reads memory trace to generate requests,and then simulates wear-leveling or error correction.At last it makes statistics and outputs results.We propose 4 strategies to resolve key problems on PCM simulation,including accuracy,complexity and speed.Firstly,it does not simulate latency.Secondly,we use the methodology of modulation design,and separate the framework and simulation of specific algorithms.Thirdly,LPCMsim is focused on simulation of wear-leveling and error correction and directly simulates accessing of memory.It ignores unessential modules,and does not simulate the process of instructions.Lastly,we optimize the simulation of different algorithms according to their characteristics.The experimental results demonstrate that the simulation time of PCM with LPCMsim is much lower than that with 2 architecuture simulators and LPCMsim is an efficient lightweight PCM simulator.To improve lifetime of PCM under malicious attacks,we improve the mapping of the region-based Start-Gap algorithm from two aspects,and call the new algorithm multi-direction Start-Gap algorithm.Firstly,it transforms the static region mapping to dynamic region mapping,so the mapping cannot be figured out and it can help PCM survive attacks.Secondly,it transforms the region-to-region mapping to region-to-all mapping,and so a logical address can be mapped to any address in the whole address space.As a result,it improves the effect of wear-leveling.We implement the multi-direction Start-Gap algorithm on LPCMsim.The experimental results demonstrate that our algorithm improves wear-leveling and can survive attacks better.