As flash memory cells age, the boundaries between cell voltages corresponding to ‘1’ and ‘0’ change. Measuring the movement with time of the voltage boundaries (or thresholds, VTH), and the confidence in the location of the boundaries (log-likelihood ratios, LLR) is critical to the reliable performance of the memory. This disclosure describes techniques for experimentally determining voltage thresholds and log-likelihood ratios values in flash memories, such that optimal VTH and LLRs can be re-computed periodically or at predetermined ages. Once re-computed, the program-erase (P/E) cycle-optimized values can be used for reading and for soft decoding until the next re-computation of VTH and LLR. The techniques can enable flash memories to have a longer effective lifespan and reliability.

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