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Weak unknown driver poisons a strongly driven net · case 04

An unknown value from a weaker driver turns a strongly driven net into x.

Member previewVariant 4 · 3 implementations · 11 checks per implementation

Case contract

Input [drivers, keeper]: drivers are [value, strength] with value in 0/1/x/z and strength weak < pull < strong. 'z' drivers are ignored. With no active driver the net is the keeper value, or 'z' when keeper is None. Otherwise only drivers at the highest present strength matter: a single agreed value wins, any disagreement (including x) gives 'x'.

Why this case matters

Resolved nets in switch-level and RTL simulators combine drivers by strength; mixing up strengths or keepers changes observed bus values.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
weak unknown under strong driver	`"x"`	`"0"`	Failed

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