Distributed XOR Protection for UECC Recovery in Nonvolatile Memory
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Solution Overview
Problem
Nonvolatile semiconductor memory devices experience high error rates, leading to uncorrectable data (UECC) that conventional Error Correction Code (ECC) and Exclusive OR (XOR) operations struggle to recover efficiently, especially when multiple portions of data are UECC, resulting in time-consuming and incomplete data recovery.
Innovation Solution
Implementing a distributed XOR scheme across multiple planes of nonvolatile memory cells, where data portions are XORed with at least two other portions and stored in dedicated XOR metablocks, enabling rapid recovery by local control circuits without relying on other FIMs, and combining XOR data with related user data to correct UECC errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ECC and single XOR operation are used for data recovery, then the system structure remains simple, but the data recovery capability is insufficient when multiple portions of data are UECC
Solution Approach 1:
The patent divides the XOR protection mechanism into multiple independent XOR operations, where each portion of user data is XORed with different combinations of other data portions to generate multiple distinct XOR data portions. This segmentation allows the system to attempt recovery through multiple independent paths, improving reliability when some recovery paths fail due to UECC conditions.
Solution Approach 2:
The patent performs multiple XOR operations during the data writing phase, preliminarily generating multiple XOR data portions and storing them in dedicated XOR metablocks. This preliminary action ensures that when read errors occur, the system already has pre-computed recovery data available locally, eliminating the need for complex real-time computations or additional read operations from other FIMs.
2Reliability
If distributed XOR scheme with multiple operations is implemented, then data recovery reliability improves, but the control circuit complexity increases
Solution Approach 1:
The patent implements local quality by dedicating specific XOR metablocks to store XOR data generated from specific user data portions within the same FIM. Each XOR metablock is locally associated with particular data recovery tasks, allowing the control circuit to efficiently select and apply appropriate XOR operations without needing to manage a monolithic, globally complex recovery structure.
3Loss of time
If XOR data is stored in dedicated XOR metablocks within the same FIM, then recovery time is reduced, but the memory structure complexity increases
Solution Approach 1:
The patent merges the user data storage and XOR protection data storage into a unified memory structure where XOR metablocks are integrated within the same FIM architecture. This merging allows the system to manage both user data and recovery data through a single, cohesive structure, reducing the overhead of inter-FIM communication and enabling faster local recovery operations.
Data Source
AI summary
An apparatus includes control circuits that are configured to connect to a plurality of nonvolatile memory cells. The control circuits are configured to determine that a first portion of user data from the plurality of memory cells that was found to be uncorrectable by ECC is unrecoverable by a first Exclusive OR (XOR) operation using first XOR data and a second portion of user data. The control circuits are further configured to, in response to the determination, recover the first portion of user data by a second XOR operation using second XOR data and a third portion of user data.