FA-89055 / Digital logic simulation / Member archive

Blocking chain reads stale pre-step values · case 05

A value computed by a blocking statement is not visible to the next statement in the same step.

Member previewVariant 5 · 3 implementations · 6 checks per implementation

Case contract

Input [regs, stmts, cycles]. Each clock step executes stmts [kind, lhs, op, a, b] in order (ops copy/inv/and/xor on 0/1). Blocking ('b') statements update the working state immediately; non-blocking ('nb') statements evaluate their right side at the statement against the working state and queue the update. After all statements, queued updates apply in statement order (last write wins). Every variable, blocking or not, keeps its value into the next step. Return per-step values sorted by variable name.

Why this case matters

Event-driven RTL simulation depends on the active/NBA region split; mis-scheduling produces races that do not exist in hardware.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
blocking chain inside one step	`[[0, 0, 0], [0, 1, 0]]`	`[[0, 0, 0], [1, 1, 1]]`	Failed

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