Flexicache: Highly Reliable and Low Power Cache under Supply Voltage Scaling

Processors supporting a wide range of supply voltages are necessary to achieve high performance in nominal supply voltage and to reduce the power consumption in low supply voltage. However, when the supply voltage is lowered below the safe margin (especially close to the threshold voltage level), the memory cell failure rate increases drastically. Thus, it is essential to provide reliability solutions for memory structures. This paper proposes a novel, reliable L1 cache design, Flexicache, which automatically configures itself for different supply voltages in order to tolerate different fault rates. Flexicache is a circuit-driven solution achieving in-cache replication with no increase in the access latency and with a minimum increase in the energy consumption. It defines three operating modes: Single Version Mode, Double Version Mode and Triple Version Mode. Compared to the best previous proposal, Flexicache can provide 34% higher energy reduction for L1 caches with 2× higher error correction capability in the low-voltage mode.