Formal Verification Cover Properties for Complete Failure Traces
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Solution Overview
Problem
Formal verification systems often fail to observe bugs in hardware designs due to limited observability of failure traces, as generated traces end prematurely when a cover property condition is triggered, missing issues that manifest later in the design's operation.
Innovation Solution
Extend cover properties in formal verification by incorporating additional conditions to ensure traces reach an effective end-of-test stage, allowing for complete observation of design failures, and optionally halt data ingress to prevent interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cover property conditions are used to terminate formal verification traces, then verification efficiency is improved by early termination, but bug observability deteriorates because traces end prematurely before failures manifest
Solution Approach 1:
The verification process is segmented into multiple phases: initial verification phase that terminates on cover property hits, and extended verification phase that continues to end-of-test. This segmentation allows efficient early termination for covered cases while enabling complete trace observation for bug detection in the extended phase.
Solution Approach 2:
The patent applies partial action by extending verification traces beyond the standard cover property termination point. This excessive action (continuing past the normal termination condition) ensures that bugs manifesting later in the test are observed, while still maintaining efficiency by not extending all traces indefinitely.
2Measurement precision
If formal verification traces are extended to end-of-test stage, then bug observability is improved by capturing complete failure manifestation, but verification time increases
Solution Approach 1:
Verification cases are segmented into two categories: those that terminate early at cover property hits (maintaining efficiency) and those that extend to end-of-test (ensuring complete bug observation). This segmentation allows the system to achieve high bug observability without uniformly increasing verification time for all cases.
Solution Approach 2:
Instead of extending all verification traces to end-of-test (excessive action), the patent extends only those traces where bugs are suspected to manifest later (partial action). This selective extension minimizes the overall verification time increase while still capturing the necessary bug observability.
3Adaptability or versatility
If data ingress continues during extended verification, then design functionality is fully tested, but trace clarity deteriorates due to interference from additional data
Solution Approach 1:
The patent extracts or removes the data ingress input signal during the extended verification phase after a cover property hit. This extraction eliminates the interference of additional data on the failure trace, allowing clear observation of the bug manifestation without the confounding factor of continued data input.
Data Source
AI summary
Cover properties are extended in formal verification to reach an effective end-of-test stage for a design under test. A formal verification task for a design under test may be received at a verification system. A cover property asserted in the formal verification task may be identified. An additional condition may be implemented for the identified cover property to extend the identified cover property to cause performance of the formal verification task to generate a trace to reach an effective end-of-test stage for the design under test in the event of a failure of the cover property.