Flash Memory Sudden Power Off Recovery Using Dummy Pages
Solution Overview
Problem
Flash memory devices face challenges in recovering interrupted data programming operations due to sudden power off events, particularly in NAND flash devices which are not random access, making it difficult to access specific addresses for command execution.
Innovation Solution
A method involving a processing unit that reads pages of a current block sequentially after a power restart, marks the last correct page, configures dummy pages, and stores data from the last correct page and its previous pages in empty pages, using a flash access interface to handle sudden power off recovery in multi-level cell or triple level cell blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sequential reading of pages is performed after power restart, then data integrity is maintained, but recovery time increases
Solution Approach 1:
The patent applies preliminary action by creating dummy pages in advance before sudden power off occurs. These dummy pages are pre-configured in the flash memory block to serve as placeholders for data that may need to be recovered. When power is restored after SPO, the recovery process can immediately utilize these pre-prepared dummy pages, eliminating the need to sequentially read and reconstruct all pages from scratch, thus reducing recovery time while maintaining data integrity
Solution Approach 2:
The patent segments the flash memory block into multiple pages with specific roles: data pages, dummy pages, and empty pages. This segmentation allows the recovery process to target only specific segments (dummy pages containing recovered data) rather than processing the entire block sequentially. The dummy pages are positioned at specific locations (e.g., pages 4-7 out of 8 total pages) to enable efficient recovery operations on segmented portions of the memory block
2Productivity
If dummy pages are configured after the next page of the last correct page, then data storage efficiency is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by assigning different functions to different regions of the flash memory block. Specifically, dummy pages are configured in specific local regions (e.g., pages 4-7) rather than uniformly throughout the entire block. This localized configuration optimizes space utilization in critical recovery areas while maintaining simpler structures in other regions. The firmware complexity is managed by implementing targeted page configuration logic that operates locally on specific page ranges rather than requiring complex global management of the entire memory block
3Reliability
If data from the last correct page and previous pages is stored in empty pages, then recovery completeness is improved, but access time increases
Solution Approach 1:
The patent applies preliminary action by pre-configuring dummy pages in specific locations before SPO occurs. These dummy pages are ready to receive recovered data immediately upon power restoration. When recovering data from the last correct page and previous pages, the system can directly write to these pre-positioned dummy pages rather than searching for or creating storage locations during recovery, thus improving recovery completeness while minimizing the access time penalty
Solution Approach 2:
The dummy pages serve as intermediary structures between the data pages and the final storage locations. During recovery, data from the last correct page and previous pages is first written to dummy pages as an intermediate step. This intermediary mechanism enables complete recovery of data while managing access time by providing a buffer zone that decouples the recovery writing process from the final data access process
Data Source
AI summary
The invention introduces a non-transitory computer program product for handling a sudden power off recovery (SPOR) to include program code to: drive a flash access interface to read pages of a current block in sequence after a power restart subsequent to a sudden power off (SPO); mark the last correct page of the current block according to page read statuses for the current block; configure n1 pages after the next page of the last correct page of the current block as dummy pages; and drive the flash access interface to store data of the last correct page and its previous n2-1 pages of the current block in empty pages after the last dummy page of the current block, wherein any of n1 and n2 is a positive integer.