Flash Memory Defect Block Management via Table Storage
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Solution Overview
Problem
Flash memory systems face issues with defective blocks that can lead to incorrect data reading when there are no more free blocks for writing, and existing solutions either lose management information during power failures or increase system complexity and cost.
Innovation Solution
A method is introduced to manage defective blocks by detecting and storing their addresses in a table block within the flash memory, setting the memory to read-only when defective blocks exceed a threshold, and allowing continued programming of free pages in defective blocks before transitioning to read-only mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If management information for bad blocks is stored in a separate memory such as EEPROM, then the reliability of defect block management is improved, but the device complexity and cost increase
Solution Approach 1:
The patent merges the defect block management information storage function into the flash memory itself by using a reserved area within the flash memory to store the defect block table. This eliminates the need for separate EEPROM or RAM components, thereby reducing device complexity and cost while maintaining the reliability of defect block management. The controller integrates both the flash memory storage and the defect management functionality in a single component.
2Ease of operation
If management information for bad blocks is stored in RAM, then the ease of operation is improved, but the reliability deteriorates due to power failure data loss
Solution Approach 1:
The patent implements preliminary action by continuously maintaining the defect block table in the reserved area of the flash memory, which is non-volatile. This ensures that defect block management information is persistently stored and automatically available after power failure, eliminating the need for re-detection while maintaining easy access through the controller's integrated management functions.
3Productivity
If defect blocks are continuously written to, then the productivity is improved, but the reliability deteriorates due to incorrect data reading
Solution Approach 1:
The patent implements feedback by having the controller check the defect block table before each write operation to determine if the target block is defective. This feedback mechanism prevents writing to defect blocks, ensuring data reading accuracy is maintained while allowing continuous writing to valid blocks, thus preserving productivity.
4Reliability
If the flash memory is set to read-only when defect blocks exceed threshold, then the reliability is improved, but the productivity deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the flash memory into valid blocks and defect blocks, managing them separately through the defect block table. This allows the system to maintain data integrity by preventing writes to defect blocks while still permitting continuous writing to valid blocks, thus avoiding complete read-only mode and preserving productivity.
Data Source
AI summary
A method for managing defect blocks in a non-volatile memory essentially comprises the steps of detecting defect blocks in the non-volatile memory, storing addresses of the defect blocks in a table block of the non-volatile memory, and setting the non-volatile memory to be read-only if the quantity of defect blocks in the non-volatile memory exceeds a threshold and no free blocks remain in the non-volatile memory. In a preferred embodiment, the free pages in the defect block continue to be programmed before setting the non-volatile memory to be read-only.