Using PCM in Next-generation Embedded Space Applications

Dynamic RAM (DRAM) has been the best technology for main memory for over thirty years. In embedded space applications, radiation hardened DRAM is needed because gamma rays cause transient errors; such rad-hard memories are extremely expensive and power hungry, leading to lower life (or increased battery weight) for satellite and other devices operating in space. Despite these problems, DRAM has been the technology of choice because it has better performance and it scales well. New, more energy efficient, non-volatile, scalable, radiation resistant memory technologies are now available, namely phase-change memory (PCM), making the DRAM choice much less compelling. However, current approaches require changes to PCM device internal circuitry, the operating system and/or the CPU cache-memory organization/interface. This paper presents a new, practical, detailed architecture, called PMMA, to effectively use PCM for main memory in next-generation embedded space systems. We designed PMMA avoiding changes to commodity PCM devices, the operating system, and the existing CPU cache-memory interface, enabling plug-in replacement of a conventional DRAM main memory by one constructed with PMMA. Our architecture incorporates novel mechanisms to address PCM´s limitations including expensive write operations, asymmetric read/write latency, and limited endurance. In our evaluation we show that PMMA achieves a 60% improvement in energy-delay over a conventional DRAM main memory.