FA-66979 / Railway interlocking logic / Member archive

Axle counter section supervision: state precedence · case 04

A section under preparatory reset is shown as ordinarily occupied while the sweep train passes.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

An axle-counter section counts axles in and out. Counting out below zero latches disturbed (count forced to 0). A reset is accepted only when the section is disturbed or the count is non-zero; it zeroes the count and enters preparatory state, which ends only when a sweep train has counted in and the count returns to zero on an out-count. query reports disturbed, prep, occupied (count>0) or clear, in that precedence.

Why this case matters

Interlocking logic decides whether trains may be given authority; a wrong decision at this point either grants unsafe movements or strands traffic.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: sweep train partly through	`["occupied", "clear"]`	`["prep", "clear"]`	Failed

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