Yielding optimized dependability assurance through bit inversion

Phase change memory (PCM) is a promising alternative to conventional DRAM main memories, due to its read performance, density, and nonvolatility and resulting low static energy. Unfortunately, reliability is still a significant challenge as limited write endurance, exacerbated by process variation, leads to increasing numbers of stuck-at faults over the memory's lifetime. This includes a significant number of stuck-at faults that appear early in the memory's service. Error-correcting Pointers (ECP) is a popular proposal to mitigate stuck-at faults in PCM by recording the addresses and the values of faulty bits in order to extend the lifetime of the memory. We propose a method to extend the effectiveness of ECP coverage called Yoda, which utilizes a small number of additional encoding bits in order to dramatically improve the effectiveness and fault correction capability of ECP. By adding one additional bit to ECP which corrects f faults, Yoda can correct 2f +1 faults. Further improvements are possible introducing small numbers additional bits. Our simulation results demonstrate that Yoda has a 3.0× improvement in fault coverage compared to a fault-aware ECP with a similar overhead, while also providing a 2.5–3.0× improvement over state-of-the-art schemes with comparable complexity. Furthermore, Yoda provides a method to protect the auxiliary bits, also with a small overhead. By adding one auxiliary bit to protect the auxiliary bits, Yoda can achieve extra improvement. •Extending pointers with partition and flip methods improve guaranteed correction capabilities.•Using small additional computational overhead decreases the number of required encoding bits.•Applying partition and flip to the auxiliary bits can allow them to operate reliably in faulty memory.•Yoda improves tolerated faults by 2.5–3.0× compared to state-of-the-art designs.