HYPNOS - Co-Design of Persistent, Energy-efficient and High-speed Embedded Processor Systems with Hybrid Volatility Memory Organisation

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Project HYPNOS explores how emerging non-volatile memory (NVM) technologies could beneficially replace not only main memory in modern embedded processor architectures, but potentially also one or multiple levels of the cache hierarchy or even the registers and how to optimize such a hybrid-volatile memory hierarchy for offering high speed and low energy tradeoffs for a multitude of application programs while providing persistence of data structures and processing state in a simple and efficient way. On the one hand, completely non-volatile (memory) processors (NVPs) that have emerged for IoT devices are known to suffer from low write times of current NVM technologies as well as by orders of magnitude lower endurance than, e.g., SRAM, thus prohibiting an operation at GHz speeds. On the other hand, existing NVM main memory computer solutions suffer from the need of the programmer to explicitly persist data structures through the cache hierarchy. HYPNOS (Named after the Greek god of sleep) systematically attacks this intertwined performance/endurance/programmability gap by taking a hardware/software co-design approach:Our investigations include techniques fora) design space exploration of hybrid NVM memory processor architectures} wrt. speed and energy consumption including hybrid (mixed volatile) register and cache-level designs,b) offering instruction-level persistence for (non-transactional) programs in case of, e.g., instantaneous power failures through low-cost and low-latency control unit (hardware) design of checkpointing and recovery functions, and additionally providingc) application-programmer (software) persistence control on a multi-core HyPNOS system for user-defined checkpointing and recovery from these and other errors or access conflicts backed by size-limited hardware transactional memory (HTM).d) The explored processor architecture designs and different types of NVM technologies will be systematically evaluated for achievable speed and energy gains, and for testing co-designed backup and recovery mechanisms, e.g., wakeup latencies, etc., using a gem5-based multi-core simulation platform and using ARM processors with HTM instruction extensions.As benchmarks, the hierarchyfrom i) simple data structures, ii) sensor (peripheral device) I/O and finally iii) transactional database applications shall be collaboratively investigated and evaluated.