Flash Memory Erased Sector Detection Using ECC Inversion
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Solution Overview
Problem
Existing flash memory systems face challenges in accurately detecting erased sectors, especially when they contain a low number of zero bits due to malfunctioning cells, leading to potential misidentification and system failure.
Innovation Solution
The method inverts the page contents, including the ECC field, to interpret an erased page with corruption as valid data, generates a new syndrome, and applies ECC correction to detect and quantify the level of corruption, allowing for the use of corrupted sectors within the ECC correction limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional ECC comparison methods are used to detect erased sectors, then detection speed is maintained, but detection accuracy deteriorates when sectors contain corrupted bits due to malfunctioning cells
Solution Approach 1:
The patent inverts the traditional approach by not directly comparing ECC fields to determine if a sector is erased. Instead, it assumes the sector is erased and attempts to correct it using ECC, then verifies if the correction succeeded. This inversion allows the system to handle corrupted bits effectively, as the correction process can tolerate a limited number of errors while still identifying truly erased sectors.
Solution Approach 2:
The patent applies ECC correction as a preliminary action before final verification. By attempting correction first and then checking if the corrected data matches the expected erased state (all 1s), the system can distinguish between genuinely erased sectors and those with corruption, improving detection accuracy without sacrificing reliability.
2Measurement precision
If all sectors are thoroughly checked for corruption, then detection accuracy improves, but system performance and speed deteriorate
Solution Approach 1:
The patent applies partial action by using ECC correction with a defined limit on the number of correctable errors. Rather than performing exhaustive checks on every bit, the system attempts correction up to the ECC capability threshold. This partial approach maintains high detection accuracy for corruptable sectors while preserving system performance by avoiding unnecessary exhaustive verification of all sectors.
3Reliability
If corrupted erased sectors are rejected, then data integrity is maintained, but storage capacity and usability deteriorate
Solution Approach 1:
The patent changes the parameter of error tolerance by allowing sectors with corrupted bits to be used for storage, provided the number of corrupted bits is within the ECC correction capability. This parameter change enables the system to maintain data integrity through correction while significantly improving storage usability by preventing rejection of recoverable sectors.
Data Source
AI summary
The present invention presents a non-volatile memory and method for its operation that allows instant and accurate detection of erased sectors when the sectors contain a low number of zero bits, due to malfunctioning cells or other problems, and the sector can still be used as the number of corrupted bits is under the ECC correction limit. This method allows the storage system to become tolerant to erased sectors corruption, as such sectors can be used for further data storage if the system can correct this error later in the written data by ECC correction.