Storage Controller Read-Level History for Faster NAND Error Correction
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Solution Overview
Problem
The operating speed of storage devices with nonvolatile memory, such as NAND flash, decreases due to the deterioration of cell distribution over time, leading to increased errors in read operations, which complicates the determination of optimal read levels and soft decision offset values for error correction decoding.
Innovation Solution
A method for operating a storage controller that involves receiving a read command, performing initial error correction decoding, and if failed, determining a new read level and soft decision offset value using predetermined methods, storing successful combinations as a history log to improve subsequent read operations, thereby enhancing error correction and reducing the need for repeated read operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple read operations are performed to determine soft decision offset value, then error correction capability is improved, but operating speed decreases
Solution Approach 1:
The patent stores the determined soft decision offset value and read level as history information in advance. When a subsequent read operation is needed, the stored history information is reused without requiring repeated read operations and soft decision offset determination, thus improving operating speed while maintaining error correction capability
Solution Approach 2:
The patent creates a copy of the determined soft decision offset value and read level parameters and stores them as history information. This copied information can be reused in future operations, avoiding the need to重新 perform the complex determination process and multiple read operations
2Device complexity
If read level is fixed in advance, then device complexity is reduced, but data reliability deteriorates due to cell distribution deterioration
Solution Approach 1:
The patent makes the read level dynamic by determining it based on the soft decision offset value that adapts to cell distribution changes. The read level is no longer fixed but adjusts according to the determined offset value, maintaining data reliability while managing complexity through automated determination and history storage
Data Source
AI summary
A method for operating a storage controller includes receiving a first read command, performing a first read of data stored in a nonvolatile memory using a first read level and receiving a first read data, performing first error correction decoding of the first read data to determine whether the first error correction decoding succeeds, determining a second read level using a predetermined method, and determining a first soft decision offset value of the second read level, reading data stored in the nonvolatile memory using the determined second read level and the first soft decision offset value and receiving a first soft decision data, performing second error correction decoding of the first soft decision data to determine whether the second error correction decoding succeeds, and storing the second read level, a first method used to determine the second read level and the first soft decision offset value.