Cache Tag Evaluation With Parallel ECC Hit-Miss Confirmation
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Solution Overview
Problem
Existing cache controllers with error detection and correction capabilities suffer performance degradation due to the need for separate pipeline stages for error evaluation and cache hit/miss determination, leading to increased latency and resource utilization.
Innovation Solution
A cache tag comparison unit that speculatively compares cache tag data with request tag data to determine a provisional cache hit or miss, followed by parallel evaluation of error detection and correction codes to verify the initial comparison, allowing for confirmation of cache hit or miss within a single pipeline stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error detection and correction codes are implemented in cache memory, then data reliability is improved, but pipeline stage complexity increases and performance degrades
Solution Approach 1:
The patent combines error detection/correction evaluation and cache tag comparison into a single unified pipeline stage. The tag comparison unit simultaneously performs speculative tag comparison and error code evaluation, merging two previously separate functions into one concurrent operation, thereby maintaining data reliability while improving cache access speed
Solution Approach 2:
The patent implements speculative tag comparison that proceeds in parallel with error code evaluation rather than waiting for error verification to complete first. This preliminary action allows the cache system to prepare hit/miss determination while error checking is ongoing, reducing overall latency
2Reliability
If error detection and correction evaluation is performed before cache tag comparison, then data reliability is improved, but pipeline stages increase and latency increases
Solution Approach 1:
The patent enables continuous cache tag comparison operation by implementing speculative comparison that does not pause for error code evaluation to complete. The tag comparison unit continuously operates by speculatively comparing tags while error evaluation proceeds in parallel, ensuring uninterrupted cache access and minimizing latency
3Measurement precision
If separate pipeline stages are used for error evaluation and cache tag comparison, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the tag comparison unit and error evaluation logic into a single integrated pipeline stage. The tag comparison unit incorporates both speculative tag comparison functionality and error code evaluation capability, reducing the number of separate pipeline stages while maintaining accurate error detection through simultaneous parallel operation
Data Source
AI summary
A cache tag comparison unit in a cache controller evaluates tag data and error correction codes to determine if there is a cache hit or miss. The cache tag comparison unit speculatively compares the tag data with the request tag without regard to error correction. The error correction code verifies whether this initial comparison is correct and provides a confirmed cache hit or miss signal. The tag data is compared with the request tag to determine a provisional cache hit or miss, and in parallel, the error correction code is evaluated. If the error code evaluation indicates errors in the tag data, a provisional cache hit is converted into a cache miss if errors are responsible for a false match. If the error code evaluation identifies the locations of errors, a provisional cache miss is converted into a cache hit if the errors are responsible for the mismatch.