Exploiting Non-Volatile Memories to Improve Reliability of Processing Element for Railway Electronic Safety Systems

The tolerance of soft errors is vital for safety related electronic systems used especially in railways as defined by EN 50,129. With evolution of fabrication technology, the probability of this problem also increased due to aggressive scaling down of the channel length of transistors. Non-volatile memories (NVMs) are considered as a part of the solution because their cells are immune against soft errors without any extra software intervention. However, there is a critical problem to replace SRAM or DRAM with NVM because of the limited write endurance. Each cell is worn out when the number of modifications exceeds the threshold. To improve the lifetime of an NVM-based memory system, we propose herein a small value encoding scheme to reduce the number of write operations. A new array, which is called encoded value array (EVA), was added beside the traditional cache structure. The EVA fills the gap between the stored data in the data array and the original data. When the gap value is small, it is written instead of updating the whole cache data to reduce the write counts. The experimental results showed that our approach increased the lifetime by 7.32 times on average.