CAM Error Recovery via Backup RAM and Replay FIFO
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Solution Overview
Problem
Content addressable memory (CAM) systems face challenges in error recovery due to the limited storage capacity and the need for efficient error detection and correction mechanisms, as they typically require extensive comparisons and have limited space for storing backup data and request results.
Innovation Solution
A method and system for CAM error recovery involving a backup random access memory (RAM) for storing data copies, a replay FIFO structure for storing match requests, and a results FIFO structure for temporarily storing results, with a master state machine that detects errors, clears incorrect results, and replays match requests using corrected data from the backup RAM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a CAM system stores data in limited capacity entries and performs extensive comparisons, then data retrieval speed is improved, but storage capacity is reduced
Solution Approach 1:
The patent implements a backup RAM that stores copies of CAM entries and a replay FIFO that stores copies of match requests. When errors are detected in CAM entries, the system retrieves correct data from the backup RAM and re-performs match requests from the replay FIFO, enabling error recovery without losing the fast comparison capability of CAM while maintaining limited storage capacity.
2Measurement precision
If a CAM system performs extensive comparisons to identify data locations, then data retrieval accuracy is improved, but device complexity is increased
Solution Approach 1:
The patent introduces a backup RAM as an intermediary storage component that holds copies of CAM entries, and a replay FIFO as an intermediary buffer that stores match requests. These intermediaries enable error detection and correction by providing fallback data sources and request buffers, maintaining high retrieval accuracy while managing system complexity through modular error recovery mechanisms.
3Reliability
If a CAM system uses limited storage space for backup data, then error recovery capability is improved, but storage capacity is reduced
Solution Approach 1:
The patent segments the storage system into multiple functional components: the primary CAM for fast data retrieval, a separate backup RAM for error recovery, a replay FIFO for request buffering, and a results FIFO for storing match results. This segmentation allows the backup storage to be dedicated specifically to error recovery without competing with the primary CAM for storage space, improving reliability while efficiently utilizing limited storage resources.
Data Source
AI summary
A method for content addressable memory (CAM) error recovery that includes detecting an error in an entry of a CAM, identifying an address of the entry in the CAM, copying data from the address in the backup random access memory (RAM) into the entry of the CAM to obtain a corrected CAM, clearing a results (first in first out) FIFO structure based on detecting the error, performing, using the corrected CAM, a match request stored in a replay FIFO structure to obtain a revised result, and storing the revised result in the results FIFO structure.