Memory carousel: LLVM-based bitwise wear leveling for nonvolatile main memory

Emerging nonvolatile memory yields, alongside many advantages, technical shortcomings, such as reduced cell lifetime. Although many wear-leveling approaches exist to extend the lifetime of such memories, usually a tradeoff for the granularity of wear leveling has to be made. Due to iterative write schemes (repeatedly sense and write), wear out of memory in certain systems is directly dependent on the written bit value and thus can be highly imbalanced, requiring dedicated bit-wise wear leveling. Such a bit-wise wear leveling so far has only be proposed together with a special hardware support. However, if no dedicated hardware solutions are available, especially for commercial off-the-shelf systems with nonvolatile memories, a software solution can be crucial for the system lifetime. In this work, we propose entirely software-based bit-wise wear leveling, where the position of bits within CPU words in the main memory is rotated on a regular basis. We leverage the LLVM intermediate representation to adjust load and store operations of the application with a custom compiler pass. Experimental evaluation shows that the lifetime by applying local rotation within the CPU word can be extended by a factor of up to 21× . We also show that our method can incorporate with coarser-grained wear leveling, e.g., on block granularity and assist achievement of higher lifetime improvements

Analysis of Dynamic Faults in Embedded-SRAMs: Implications for Memory Test

International audienceThis paper presents the results of resistive-open defect insertion in different locations of Infineon 0.13 μm embedded-SRAM with the main purpose of verifying the presence of dynamic faults. This study is based on the injection of resistive defects as their presence in VDSM technologies is more and more frequent. Electrical simulations have been performed to evaluate the effects of those defects in terms of detected functional faults. Read destructive, deceptive read destructive and dynamic read destructive faults have been reproduced and accurately characterized. The dependence of the fault detection has been put in relation with memory operating conditions, resistance value and clock cycle, and the importance of at speed testing for dynamic fault models has been pointed out. Finally resistive Address Decoder Open Faults (ADOF) have been simulated and the conditions that maximize the fault detection have been discussed as well as the resulting implications for memory test