Flash Memory Controller Rewriting Count Tracking

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Solution Overview

Problem

Conventional semiconductor recording devices face issues with data retention property deterioration and error accumulation due to increased rewriting times, especially with power shutdowns, which affect the reliability and accuracy of recording the number of rewritings in flash memory.

Innovation Solution

A memory controller and semiconductor recording device that divide nonvolatile memory into two regions: one for user data and another for tracking the number of updates, using an empty block management table and rewriting number conversion to manage physical blocks and notify the host apparatus of total rewriting times, thereby improving data retention and error handling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If the number of rewriting times increases to extend memory card life, then the usable capacity and rewriting flexibility improve, but data retention property deteriorates and errors accumulate due to power shutdowns

Engineering Contradiction:

Improvememory card lifeVSAvoiddata retention property

Core Design Contradiction:

Duration of action of moving objectVSReliability

Solution Approach 1:

The patent segments the memory card into two distinct regions: a first region for user data storage and a second region for storing rewriting count information. This segmentation allows independent management of data storage and rewriting tracking, preventing errors in one region from affecting the other and maintaining data retention reliability even as rewriting times increase.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediary mechanism (the second region dedicated to storing rewriting counts) that mediates between the act of rewriting user data and the need to track rewriting times. This intermediary region isolates the rewriting count storage from user data, preventing error accumulation in the critical data retention area while enabling accurate tracking of rewriting times.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If rewriting is performed frequently to maximize memory utilization, then productivity improves, but writing errors occur more frequently after 100,000 rewrites

Engineering Contradiction:

Improvememory utilizationVSAvoidwriting error rate

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent performs preliminary action by pre-allocating a second region specifically for storing rewriting count information before any rewriting operations begin. This preparation ensures that rewriting counts are tracked from the start, allowing the system to monitor and manage rewriting times proactively, thereby preventing writing errors by identifying when blocks approach their rewriting limits.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements a feedback mechanism where the rewriting count stored in the second region is continuously updated and referenced during rewriting operations. This feedback allows the system to track the number of rewrites, identify when blocks are approaching their reliability limits, and take appropriate actions to prevent writing errors, thus maintaining high productivity without sacrificing reliability.

Inventive Principle:

Principle #23Feedback

3Duration of action of moving object

If conventional leveling is applied to increase rewriting times, then the number of rewriting times increases, but the actual rewriting count cannot be recorded and life time cannot be informed to users

Engineering Contradiction:

Improvenumber of rewriting timesVSAvoidrewriting count visibility

Core Design Contradiction:

Duration of action of moving objectVSLoss of information

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent enables the memory card to self-monitor and self-report its rewriting count through the second region. The system automatically tracks and stores rewriting times without external intervention, and this information can be read back to inform users of the actual rewriting count and remaining life time, eliminating the information loss present in conventional leveling methods.

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS8397015B2Memory controller, semiconductor recording device, and method for notifying the number of times of rewriting

Publication Date: 2013.03.12 PANASONIC HOLDINGS CORP

AI summary

User data transferred from a host apparatus and a first information table 35 indicating correspondence between a logical address and a physical address are recorded in a first region of a flash memory 20. A second information table 38 composed of the physical block address storing the first information table 35 and the number of times of update of the physical block for recording the first information table from the time of manufacturing is recorded in a second region of the flash memory 20. The physical blocks of the first and the second regions are recorded independently from each other in a rotational manner. According to the recording of the second information table, the total number of times of rewriting of the first region is converted. This can suppress the number of times of rewriting of the second region and improve reliability of the number of times of update of the first information table from the time of manufacturing, the number being recorded in the second region.