FAILURE MAP
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FA-92261 / PLC ladder logic scan cycles / Open access

Free-running clock timer captures its start tick while disabled · case 01

After an idle period the timer finishes immediately because time before the enable is counted.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The disabled path records the current clock as the start tick.

THE FAILURE

The disabled path records the current clock as the start tick.

Unsuccessful approach: Capturing only when no start is stored still keeps a stale start from an earlier idle period.

Case contract

Delay timer built on a 16-bit free-running clock register (ticks wrap from 65535 to 0). samples is a list of [enable, clock] read each scan. The first enabled scan captures the start tick; elapsed is (clock - start) modulo 65536. Done latches once elapsed >= preset and stays set while enabled even if the elapsed value later wraps. A disabled scan clears start and done. Return [done, elapsed capped at preset once done] per scan, [False, 0] when disabled.

Why this case matters

Ladder programs are executed as repeated scans; each defect here changes what a rung, timer, counter or data-table instruction reports on a particular scan, which is how commissioning and field faults are actually observed.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(preset, samples):
    start = None
    done = False
    out = []
    for enable, clock in samples:
        if not enable:
            start = clock
            done = False
            out.append([False, 0])
            continue
        if start is None:
            start = clock
        elapsed = (clock - start) & 0xFFFF
        if elapsed >= preset:
            done = True
        out.append([done, preset if done else elapsed])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 1',
   [100,
    [[True, 53593],
     [True, 53635],
     [True, 10212],
     [False, 10250],
     [True, 24553],
     [True, 35364],
     [True, 35501],
     [True, 35591],
     [True, 65279],
     [True, 65379],
     [True, 65509]]],
   [[False, 0],
    [False, 42],
    [True, 100],
    [False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: scenario 2',
   [100,
    [[True, 17304],
     [True, 20531],
     [True, 27559],
     [False, 57396],
     [True, 19489],
     [True, 46000],
     [True, 46035],
     [True, 46209],
     [True, 5526]]],
   [[False, 0],
    [True, 100],
    [True, 100],
    [False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100]]],
  ['regression: scenario 3',
   [40000,
    [[True, 42783],
     [False, 4625],
     [True, 4670],
     [True, 8857],
     [False, 15422],
     [False, 15500],
     [True, 15560],
     [True, 27335],
     [True, 27471]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 4187],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 11775],
    [False, 11911]]],
  ['control: scenario 4',
   [100,
    [[True, 2607],
     [True, 18576],
     [True, 18609],
     [True, 18619],
     [True, 45272],
     [True, 45282],
     [True, 55824],
     [False, 61503]]],
   [[False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [False, 0]]]],
 [['regression: scenario 1',
   [1000,
    [[False, 39404],
     [False, 39599],
     [True, 39752],
     [True, 39914],
     [False, 49270],
     [True, 53547],
     [True, 53700],
     [True, 4426]]],
   [[False, 0], [False, 0], [False, 0], [False, 162], [False, 0], [False, 0], [False, 153], [True, 1000]]],
  ['regression: scenario 2',
   [5,
    [[True, 40525],
     [True, 40666],
     [True, 40725],
     [True, 58227],
     [True, 18319],
     [False, 25775],
     [True, 25797],
     [True, 25799]]],
   [[False, 0], [True, 5], [True, 5], [True, 5], [True, 5], [False, 0], [False, 0], [False, 2]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 3',
   [5,
    [[False, 30258],
     [True, 30296],
     [True, 45510],
     [True, 2343],
     [True, 12538],
     [True, 12596],
     [False, 12635],
     [True, 37410],
     [True, 53676],
     [True, 10497],
     [True, 10628],
     [False, 10824],
     [True, 27527],
     [True, 55148]]],
   [[False, 0],
    [False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [False, 0],
    [False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [False, 0],
    [False, 0],
    [True, 5]]],
  ['regression: scenario 4',
   [65535,
    [[True, 43066],
     [True, 60153],
     [False, 2292],
     [True, 2392],
     [True, 12076],
     [False, 28626],
     [False, 28693],
     [False, 45850],
     [True, 5636]]],
   [[False, 0],
    [False, 17087],
    [False, 0],
    [False, 0],
    [False, 9684],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0]]]],
 [['regression: scenario 2',
   [40000,
    [[True, 54821],
     [True, 18035],
     [True, 32212],
     [True, 38340],
     [True, 38521],
     [True, 38565],
     [True, 38691],
     [True, 52834],
     [True, 6573],
     [False, 6717],
     [True, 13602]]],
   [[False, 0],
    [False, 28750],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [False, 0],
    [False, 0]]],
  ['regression: scenario 3',
   [5,
    [[False, 23870],
     [True, 46782],
     [True, 46917],
     [True, 46976],
     [True, 56255],
     [True, 61627],
     [True, 1767],
     [True, 1874]]],
   [[False, 0], [False, 0], [True, 5], [True, 5], [True, 5], [True, 5], [True, 5], [True, 5]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 1',
   [100,
    [[False, 22859],
     [True, 23009],
     [True, 46893],
     [True, 47082],
     [True, 47173],
     [True, 47274],
     [False, 47358],
     [True, 47448],
     [True, 54303],
     [True, 54477],
     [False, 54574]]],
   [[False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100],
    [False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [False, 0]]],
  ['control: scenario 4',
   [5,
    [[True, 25219],
     [True, 25303],
     [True, 25491],
     [True, 33180],
     [True, 33370],
     [True, 34085],
     [True, 35832],
     [True, 46392],
     [True, 48652],
     [True, 48709],
     [True, 6073],
     [True, 6100]]],
   [[False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5]]]],
 [['regression: scenario 3',
   [65535,
    [[False, 15447],
     [True, 18837],
     [False, 18898],
     [True, 19006],
     [False, 33164],
     [True, 33164],
     [True, 41175],
     [True, 53503],
     [True, 53600],
     [True, 6331],
     [True, 35575],
     [True, 35594],
     [True, 35643]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 8011],
    [False, 20339],
    [False, 20436],
    [False, 38703],
    [False, 2411],
    [False, 2430],
    [False, 2479]]],
  ['regression: scenario 4',
   [40000,
    [[False, 63428],
     [False, 10454],
     [True, 36085],
     [False, 36231],
     [True, 36344],
     [True, 36357],
     [True, 36437],
     [True, 36476],
     [True, 59214],
     [False, 59324],
     [True, 23687],
     [True, 45223],
     [False, 61971]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 13],
    [False, 93],
    [False, 132],
    [False, 22870],
    [False, 0],
    [False, 0],
    [False, 21536],
    [False, 0]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 1',
   [65535,
    [[False, 3784],
     [False, 8211],
     [False, 33966],
     [True, 50163],
     [True, 63009],
     [False, 63184],
     [True, 63243],
     [True, 63325]]],
   [[False, 0], [False, 0], [False, 0], [False, 0], [False, 12846], [False, 0], [False, 0], [False, 82]]],
  ['regression: scenario 2',
   [1000,
    [[False, 46148],
     [True, 57365],
     [False, 57416],
     [True, 57439],
     [True, 57613],
     [True, 57776],
     [True, 61872],
     [True, 62038],
     [True, 9532],
     [True, 32841],
     [True, 32973]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 174],
    [False, 337],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000]]]],
 [['regression: scenario 5',
   [100,
    [[True, 65059],
     [True, 12093],
     [True, 36229],
     [True, 36982],
     [False, 57476],
     [True, 57575],
     [True, 12126],
     [True, 20887],
     [False, 28367]]],
   [[False, 0],
    [True, 100],
    [True, 100],
    [True, 100],
    [False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [False, 0]]],
  ['regression: scenario 6',
   [5,
    [[True, 49632],
     [True, 11081],
     [True, 11114],
     [True, 11176],
     [True, 11291],
     [False, 25142],
     [True, 49288],
     [True, 49464],
     [True, 49662],
     [True, 56076],
     [True, 56119],
     [False, 62264]]],
   [[False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [False, 0],
    [False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [False, 0]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 1',
   [40000,
    [[True, 14860],
     [True, 43167],
     [True, 43310],
     [True, 43470],
     [False, 65246],
     [False, 2333],
     [True, 20092],
     [True, 45967],
     [False, 64834],
     [True, 20225],
     [False, 20250],
     [True, 21773],
     [True, 26780]]],
   [[False, 0],
    [False, 28307],
    [False, 28450],
    [False, 28610],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 25875],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 5007]]],
  ['regression: scenario 2',
   [1000,
    [[True, 51184],
     [True, 56535],
     [True, 13279],
     [True, 24517],
     [True, 24685],
     [True, 32146],
     [True, 59255],
     [False, 21739],
     [True, 21822],
     [True, 43196]]],
   [[False, 0],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [False, 0],
    [False, 0],
    [True, 1000]]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: enable after idle[[False, 0], [False, 0], [True, 50], [True, 50], [True, 50]][[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]Failed
regression: scenario 1[[False, 0], [False, 42], [True, 100], [False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100]][[False, 0], [False, 42], [True, 100], [False, 0], [False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100]]Failed
control: clock wrap[[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]][[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]Passed
control: long enable past a full wrap[[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]][[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]Passed
control: elapsed returns to zero[[False, 0], [True, 5], [True, 5], [True, 5]][[False, 0], [True, 5], [True, 5], [True, 5]]Passed
regression: scenario 2[[False, 0], [True, 100], [True, 100], [False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100]][[False, 0], [True, 100], [True, 100], [False, 0], [False, 0], [True, 100], [True, 100], [True, 100], [True, 100]]Failed
regression: scenario 3[[False, 0], [False, 0], [False, 45], [False, 4232], [False, 0], [False, 0], [False, 60], [False, 11835], [False, 11971]][[False, 0], [False, 0], [False, 0], [False, 4187], [False, 0], [False, 0], [False, 0], [False, 11775], [False, 11911]]Failed
control: scenario 4[[False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [False, 0]][[False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [False, 0]]Passed

SHA-256 / a821e1d923e0da6a00a2213c7252ab13a41117472de55c88b3bcea64b62763ba

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(preset, samples):
    start = None
    done = False
    out = []
    for enable, clock in samples:
        if not enable:
            if start is None:
                start = clock
            done = False
            out.append([False, 0])
            continue
        if start is None:
            start = clock
        elapsed = (clock - start) & 0xFFFF
        if elapsed >= preset:
            done = True
        out.append([done, preset if done else elapsed])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 1',
   [100,
    [[True, 53593],
     [True, 53635],
     [True, 10212],
     [False, 10250],
     [True, 24553],
     [True, 35364],
     [True, 35501],
     [True, 35591],
     [True, 65279],
     [True, 65379],
     [True, 65509]]],
   [[False, 0],
    [False, 42],
    [True, 100],
    [False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: scenario 2',
   [100,
    [[True, 17304],
     [True, 20531],
     [True, 27559],
     [False, 57396],
     [True, 19489],
     [True, 46000],
     [True, 46035],
     [True, 46209],
     [True, 5526]]],
   [[False, 0],
    [True, 100],
    [True, 100],
    [False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100]]],
  ['regression: scenario 3',
   [40000,
    [[True, 42783],
     [False, 4625],
     [True, 4670],
     [True, 8857],
     [False, 15422],
     [False, 15500],
     [True, 15560],
     [True, 27335],
     [True, 27471]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 4187],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 11775],
    [False, 11911]]],
  ['control: scenario 4',
   [100,
    [[True, 2607],
     [True, 18576],
     [True, 18609],
     [True, 18619],
     [True, 45272],
     [True, 45282],
     [True, 55824],
     [False, 61503]]],
   [[False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [False, 0]]]],
 [['regression: scenario 1',
   [1000,
    [[False, 39404],
     [False, 39599],
     [True, 39752],
     [True, 39914],
     [False, 49270],
     [True, 53547],
     [True, 53700],
     [True, 4426]]],
   [[False, 0], [False, 0], [False, 0], [False, 162], [False, 0], [False, 0], [False, 153], [True, 1000]]],
  ['regression: scenario 2',
   [5,
    [[True, 40525],
     [True, 40666],
     [True, 40725],
     [True, 58227],
     [True, 18319],
     [False, 25775],
     [True, 25797],
     [True, 25799]]],
   [[False, 0], [True, 5], [True, 5], [True, 5], [True, 5], [False, 0], [False, 0], [False, 2]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 3',
   [5,
    [[False, 30258],
     [True, 30296],
     [True, 45510],
     [True, 2343],
     [True, 12538],
     [True, 12596],
     [False, 12635],
     [True, 37410],
     [True, 53676],
     [True, 10497],
     [True, 10628],
     [False, 10824],
     [True, 27527],
     [True, 55148]]],
   [[False, 0],
    [False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [False, 0],
    [False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [False, 0],
    [False, 0],
    [True, 5]]],
  ['regression: scenario 4',
   [65535,
    [[True, 43066],
     [True, 60153],
     [False, 2292],
     [True, 2392],
     [True, 12076],
     [False, 28626],
     [False, 28693],
     [False, 45850],
     [True, 5636]]],
   [[False, 0],
    [False, 17087],
    [False, 0],
    [False, 0],
    [False, 9684],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0]]]],
 [['regression: scenario 2',
   [40000,
    [[True, 54821],
     [True, 18035],
     [True, 32212],
     [True, 38340],
     [True, 38521],
     [True, 38565],
     [True, 38691],
     [True, 52834],
     [True, 6573],
     [False, 6717],
     [True, 13602]]],
   [[False, 0],
    [False, 28750],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [False, 0],
    [False, 0]]],
  ['regression: scenario 3',
   [5,
    [[False, 23870],
     [True, 46782],
     [True, 46917],
     [True, 46976],
     [True, 56255],
     [True, 61627],
     [True, 1767],
     [True, 1874]]],
   [[False, 0], [False, 0], [True, 5], [True, 5], [True, 5], [True, 5], [True, 5], [True, 5]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 1',
   [100,
    [[False, 22859],
     [True, 23009],
     [True, 46893],
     [True, 47082],
     [True, 47173],
     [True, 47274],
     [False, 47358],
     [True, 47448],
     [True, 54303],
     [True, 54477],
     [False, 54574]]],
   [[False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [True, 100],
    [True, 100],
    [False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [False, 0]]],
  ['control: scenario 4',
   [5,
    [[True, 25219],
     [True, 25303],
     [True, 25491],
     [True, 33180],
     [True, 33370],
     [True, 34085],
     [True, 35832],
     [True, 46392],
     [True, 48652],
     [True, 48709],
     [True, 6073],
     [True, 6100]]],
   [[False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5]]]],
 [['regression: scenario 3',
   [65535,
    [[False, 15447],
     [True, 18837],
     [False, 18898],
     [True, 19006],
     [False, 33164],
     [True, 33164],
     [True, 41175],
     [True, 53503],
     [True, 53600],
     [True, 6331],
     [True, 35575],
     [True, 35594],
     [True, 35643]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 8011],
    [False, 20339],
    [False, 20436],
    [False, 38703],
    [False, 2411],
    [False, 2430],
    [False, 2479]]],
  ['regression: scenario 4',
   [40000,
    [[False, 63428],
     [False, 10454],
     [True, 36085],
     [False, 36231],
     [True, 36344],
     [True, 36357],
     [True, 36437],
     [True, 36476],
     [True, 59214],
     [False, 59324],
     [True, 23687],
     [True, 45223],
     [False, 61971]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 13],
    [False, 93],
    [False, 132],
    [False, 22870],
    [False, 0],
    [False, 0],
    [False, 21536],
    [False, 0]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 1',
   [65535,
    [[False, 3784],
     [False, 8211],
     [False, 33966],
     [True, 50163],
     [True, 63009],
     [False, 63184],
     [True, 63243],
     [True, 63325]]],
   [[False, 0], [False, 0], [False, 0], [False, 0], [False, 12846], [False, 0], [False, 0], [False, 82]]],
  ['regression: scenario 2',
   [1000,
    [[False, 46148],
     [True, 57365],
     [False, 57416],
     [True, 57439],
     [True, 57613],
     [True, 57776],
     [True, 61872],
     [True, 62038],
     [True, 9532],
     [True, 32841],
     [True, 32973]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 174],
    [False, 337],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000]]]],
 [['regression: scenario 5',
   [100,
    [[True, 65059],
     [True, 12093],
     [True, 36229],
     [True, 36982],
     [False, 57476],
     [True, 57575],
     [True, 12126],
     [True, 20887],
     [False, 28367]]],
   [[False, 0],
    [True, 100],
    [True, 100],
    [True, 100],
    [False, 0],
    [False, 0],
    [True, 100],
    [True, 100],
    [False, 0]]],
  ['regression: scenario 6',
   [5,
    [[True, 49632],
     [True, 11081],
     [True, 11114],
     [True, 11176],
     [True, 11291],
     [False, 25142],
     [True, 49288],
     [True, 49464],
     [True, 49662],
     [True, 56076],
     [True, 56119],
     [False, 62264]]],
   [[False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [False, 0],
    [False, 0],
    [True, 5],
    [True, 5],
    [True, 5],
    [True, 5],
    [False, 0]]],
  ['control: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['control: long enable past a full wrap',
   [1000, [[True, 100], [True, 30100], [True, 60100], [True, 24564], [True, 700]]],
   [[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]],
  ['control: elapsed returns to zero',
   [5, [[True, 10], [True, 20], [True, 10], [True, 12]]],
   [[False, 0], [True, 5], [True, 5], [True, 5]]],
  ['regression: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['regression: scenario 1',
   [40000,
    [[True, 14860],
     [True, 43167],
     [True, 43310],
     [True, 43470],
     [False, 65246],
     [False, 2333],
     [True, 20092],
     [True, 45967],
     [False, 64834],
     [True, 20225],
     [False, 20250],
     [True, 21773],
     [True, 26780]]],
   [[False, 0],
    [False, 28307],
    [False, 28450],
    [False, 28610],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 25875],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 5007]]],
  ['regression: scenario 2',
   [1000,
    [[True, 51184],
     [True, 56535],
     [True, 13279],
     [True, 24517],
     [True, 24685],
     [True, 32146],
     [True, 59255],
     [False, 21739],
     [True, 21822],
     [True, 43196]]],
   [[False, 0],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [True, 1000],
    [False, 0],
    [False, 0],
    [True, 1000]]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: enable after idle[[False, 0], [False, 0], [True, 50], [True, 50], [True, 50]][[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]Failed
regression: scenario 1[[False, 0], [False, 42], [True, 100], [False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100]][[False, 0], [False, 42], [True, 100], [False, 0], [False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100]]Failed
control: clock wrap[[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]][[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]Passed
control: long enable past a full wrap[[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]][[False, 0], [True, 1000], [True, 1000], [True, 1000], [True, 1000]]Passed
control: elapsed returns to zero[[False, 0], [True, 5], [True, 5], [True, 5]][[False, 0], [True, 5], [True, 5], [True, 5]]Passed
regression: scenario 2[[False, 0], [True, 100], [True, 100], [False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100]][[False, 0], [True, 100], [True, 100], [False, 0], [False, 0], [True, 100], [True, 100], [True, 100], [True, 100]]Failed
regression: scenario 3[[False, 0], [False, 0], [False, 27423], [False, 31610], [False, 0], [False, 0], [False, 38313], [True, 40000], [True, 40000]][[False, 0], [False, 0], [False, 0], [False, 4187], [False, 0], [False, 0], [False, 0], [False, 11775], [False, 11911]]Failed
control: scenario 4[[False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [False, 0]][[False, 0], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [True, 100], [False, 0]]Passed

SHA-256 / 31cd6f21d27875a4e35448a4a6fc5cd1f6f59f03c7876d56f68b33d9d97cb2f4

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

A deterministic bounded teaching model of one PLC instruction or rung pattern evaluated scan by scan. The stated contract is a stipulated toy convention, not a claim of conformance to any vendor controller or IEC 61131-3 runtime. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:51:43.940159+00:00.

Case digest / 504e97650a142a3d2cbee0c6f0591a3443da3e5cfac530da107fa4fd2b2772c4