Cache Directory Stuck Bit Detection and Defective Member Marking
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Solution Overview
Problem
Conventional methods for handling hard errors in cache directories are inefficient, as they often require redundant circuitry that wastes space and degrades system performance, and existing error correction techniques either fail to correct stuck bits or repeatedly attempt to correct errors without success, leading to system downtime.
Innovation Solution
A method that detects stuck bits in cache directory tags, marks defective members, and routes address information through error-correction pipeline circuitry to temporarily store and transmit corrected data, ensuring directory integrity without penalizing access time and using redundant structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant circuitry is used to handle hard errors in cache directories, then reliability is improved, but device complexity and space consumption increase
Solution Approach 1:
The patent extracts the error correction function from redundant hardware circuitry and implements it through software-based detection and marking mechanisms. By identifying stuck bits through error detection and marking defective members, the system eliminates the need for extensive redundant circuitry while maintaining reliability.
Solution Approach 2:
The cache directory system performs self-diagnosis and self-correction by detecting errors in its own tags, marking defective members, and excluding them from future operations. This self-service approach reduces the need for external redundant hardware while maintaining system reliability.
2Reliability
If conventional error correction techniques are used, then some errors can be corrected, but stuck bits cannot be corrected and system downtime increases
Solution Approach 1:
The system performs preliminary detection and marking of defective members before they cause system-wide failures. By detecting stuck bits and marking affected directory members in advance, the system prevents future operational failures and reduces downtime.
Solution Approach 2:
The patent implements feedback mechanisms where error detection results are used to mark defective members, which then feed back into the exclusion logic to prevent future errors. This closed-loop approach ensures that stuck bits are accounted for and prevent system downtime.
3Reliability
If error correction is attempted repeatedly, then more errors can be detected, but access time is penalized and performance degrades
Solution Approach 1:
Instead of attempting full error correction on every access, the system performs partial action by pre-marking known defective members. This allows the system to skip unnecessary correction operations for marked members, maintaining reliability while avoiding performance penalties from excessive correction attempts.
Data Source
AI summary
A method of handling a stuck bit in a directory of a cache memory which detects an error in a stored tag having an address field, a state field and an error-correction field, determines that the error is associated with a stuck bit of the directory member, marks the directory member as defective, and casts out corrected address information. The error is detected during processing of a cache directory access request, and is determined to be associated with a stuck bit of the directory member by attempting to correct a first error and then detecting a second error after the first correction attempt. The address information is cast out by routing a surrogate tag contained in a surrogate member of the cache directory through error-correction pipeline circuitry while transmitting the address information from the surrogate member to a cast-out machine.