Flash Memory Page Scanning for Reliable Erased Area Detection
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Solution Overview
Problem
Flash memory systems face challenges in identifying and managing pages that are not fully programmed due to low host writing activity or power cycles, leading to inefficiencies in data storage and retrieval.
Innovation Solution
A method and system utilizing ECC and EDC decoders to scan flash memory blocks by identifying pages with all bits set to '1' as erased and those with mixed bit states as programmed, allowing for efficient determination of the last programmed page through a decoding and verification process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single decoder is used to read flash memory pages, then the device complexity is reduced, but the reliability of identifying erased pages deteriorates
Solution Approach 1:
The patent combines two decoders (first decoder for initial decoding and second decoder for verification) into a unified scanning process. This merging allows the system to maintain high reliability by cross-verifying decoded data while managing complexity through integrated control logic that coordinates both decoders in a systematic scanning approach.
Solution Approach 2:
The patent implements a feedback mechanism where the first decoder's output is verified by the second decoder. The verification results feed back into the identification process, allowing the system to confirm whether a page is truly erased or contains valid data. This feedback loop ensures reliable erased page identification even when individual decoder readings may be ambiguous.
2Measurement precision
If comprehensive verification of decoded data is performed, then the measurement precision of page state identification is improved, but the loss of time increases
Solution Approach 1:
The patent performs preliminary decoding with the first decoder before conducting the more time-consuming verification with the second decoder. This preliminary action allows the system to quickly identify candidate erased pages that warrant further verification, reducing the overall scanning time by avoiding exhaustive verification of all pages while maintaining high identification accuracy for pages that require it.
Solution Approach 2:
The patent applies different levels of verification to different pages based on local characteristics. Pages that show strong indicators of being erased undergo full two-decoder verification for high precision, while pages with ambiguous characteristics may be handled with less intensive verification. This localized quality approach balances measurement precision with time efficiency across the entire flash memory scan.
Data Source
AI summary
The subject technology provides for scanning blocks of a flash memory device for erased pages. A first codeword read from a page of a block in a flash memory device is received and provided to a first decoder for decoding. In response to receiving a first success indicator from the first decoder indicating that the first codeword was successfully decoded, first decoded data is provided from the first decoder to a second decoder for verification of the first decoded data. In response to receiving a first failure indicator from the second decoder indicating that the first decoded data was not verified, the page of the block is identified as being in an erased state based on the first success indicator received from the first decoder and the first failure indicator received from the second decoder.