DETERMINISTIC READ RETRY METHOD FOR SOFT LDPC DECODING IN FLASH MEMORIES

摘要

A method is disclosed for performing LDPC soft decoding of data stored in a flash storage device. Upon occurrence of a hard read failure, one or more retries with soft decoding after each retry are performed until soft decoding is successful or a maximum iteration count is reached. For each retry thresholds for sensing a level of a cell are adjusted according to a specific sequence. Likewise, the LLR table for each retry is selected from pre-determined LLR tables each corresponding to a retry attempt and the thresholds used for the retry attempt. The LLR table is not adjusted between retries or based on outcomes of any retries. A step size by which thresholds adjusted may be tuned to improve performance.

主权项

1. A computer system comprising a processor and a storage device, the processor programmed to:
(a) perform an initial read of a code word from a plurality of cells of the storage device using one or more threshold levels; (b) adjust the one or more threshold levels to obtain one or more current threshold levels based on an iteration count; (c) retry reading the code word from the plurality of cells of the storage device using the one or more current threshold levels; (d) attempt to decode the code word using a log likelihood ratio (LLR) table of a plurality of LLR tables, outcomes of the initial read (a) and one or more retry readings (d), each LLR table of the plurality of LLR tables corresponding to the iteration count; and (e) if attempting to decode the code word at (c) is unsuccessful and the iteration count is less than a maximum iteration count, repeat steps (b) through (e).