Memory System Erased State Persistence Across Power Cycles
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Solution Overview
Problem
Existing memory systems face challenges in erasing data in read-only mode, where non-volatile data retention is restricted, and maintaining an erased state during power cycling, as volatile memory loses initialization information.
Innovation Solution
A memory system configuration that includes a non-volatile memory for storing user data and lookup table initialization information, and a volatile memory for temporary data storage, where the controller manages logical-to-physical address conversions and initializes the lookup tables based on stored initialization information to maintain the erased state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is erased from non-volatile memory in read-only mode, then data security is improved, but the ability to maintain erased state across power cycles deteriorates
Solution Approach 1:
The memory system is divided into two distinct memory areas: a first area for storing user data and a second area for storing lookup table initialization information. This segmentation allows independent management of data storage and erasure verification, enabling secure erasure in read-only mode while maintaining state persistence through separate initialization information storage.
Solution Approach 2:
The system performs preliminary action by storing lookup table initialization information in the second area before power cycling occurs. During startup, the controller reads this pre-stored initialization information and uses it to initialize the lookup tables, thereby reconstructing the erased state without requiring actual data rewriting. This preliminary storage of initialization information enables the system to maintain the erased state across power cycles.
2Speed
If volatile memory is used for lookup table storage, then access speed is improved, but data retention during power cycling deteriorates
Solution Approach 1:
The second area of non-volatile memory acts as an intermediary between the volatile memory and permanent storage. It stores lookup table initialization information that serves as a bridge, allowing the volatile memory to be quickly initialized upon power-up without requiring persistent storage of the entire lookup table. This intermediary storage enables both fast access (through volatile memory) and state persistence (through non-volatile initialization information).
Solution Approach 2:
Instead of storing the complete lookup table in volatile memory, the system stores only the essential initialization information in the second area of non-volatile memory. During startup, this compact initialization information is read and used to reconstruct or initialize the full lookup table in volatile memory. This copying approach reduces the storage burden on volatile memory while ensuring rapid access performance.
3Reliability
If read-only mode is enforced for data protection, then data integrity is improved, but the ability to perform erasure operations deteriorates
Solution Approach 1:
The system extracts the erasure verification function from the main data storage area by creating a separate second area dedicated to storing lookup table initialization information. This extracted functionality allows erasure operations to be performed and verified in the read-only first area while maintaining the ability to initialize and verify erasure status using the separate initialization information in the second area, thereby preserving both data integrity and erasure capability.
Solution Approach 2:
The system implements self-service by using the initialization information stored in the second area to automatically verify and maintain the erased state of the first area. During startup, the controller reads the initialization information and uses it to initialize the lookup tables, thereby self- verifying the erasure status without requiring external intervention or writing to the read-only first area. This self-service mechanism maintains data integrity while enabling erasure operations.
Data Source
AI summary
According to one embodiment, a memory system includes: a non-volatile memory including a first area configured to hold first data received from an outside and a second area configured to hold second data; a volatile memory; and a controller. The non-volatile memory holds third data that associates a first address of the first data assigned to an instruction received from an outside with a second address of the first data that specifies a part of the first area. As a startup operation, the controller reads the third data from the non-volatile memory and holds the third data as fourth data in the volatile memory. The controller erases the fourth data from the volatile memory when the second data is held in the second area.