FAILURE MAP
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FA-92251 / PLC ladder logic scan cycles / Open access

Free-running clock timer mishandles the tick counter rollover · case 01

A delay that spans the 65535-to-0 rollover reports negative elapsed time and never finishes.

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

ROOT CAUSE

Elapsed is computed as a plain difference without modulo-65536 wrap.

THE FAILURE

Elapsed is computed as a plain difference without modulo-65536 wrap.

Unsuccessful approach: Taking the absolute difference measures the wrong interval across the rollover.

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 = None
            done = False
            out.append([False, 0])
            continue
        if start is None:
            start = clock
        elapsed = clock - start
        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: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['regression: scenario 6',
   [40000,
    [[True, 63614],
     [True, 63728],
     [True, 22150],
     [True, 22324],
     [True, 22510],
     [True, 22616],
     [True, 22811],
     [True, 26381],
     [True, 40962],
     [True, 4300],
     [True, 4446],
     [True, 6819]]],
   [[False, 0],
    [False, 114],
    [False, 24072],
    [False, 24246],
    [False, 24432],
    [False, 24538],
    [False, 24733],
    [False, 28303],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000]]],
  ['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]]],
  ['control: 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: 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]]],
  ['control: 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]]]],
 [['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 9',
   [65535,
    [[True, 50243],
     [True, 50414],
     [True, 54443],
     [True, 54585],
     [True, 54684],
     [False, 63787],
     [True, 63849],
     [True, 7734]]],
   [[False, 0],
    [False, 171],
    [False, 4200],
    [False, 4342],
    [False, 4441],
    [False, 0],
    [False, 0],
    [False, 9421]]],
  ['regression: 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]]],
  ['control: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['control: 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: 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 5',
   [5,
    [[True, 36141],
     [True, 56668],
     [False, 56831],
     [True, 56893],
     [True, 6106],
     [True, 24708],
     [True, 45326],
     [True, 65076],
     [True, 65184]]],
   [[False, 0], [True, 5], [False, 0], [False, 0], [True, 5], [True, 5], [True, 5], [True, 5], [True, 5]]],
  ['regression: scenario 9',
   [65535,
    [[True, 44901],
     [False, 62429],
     [True, 62596],
     [True, 62792],
     [True, 21296],
     [True, 21309],
     [False, 21419],
     [False, 21455],
     [True, 21477]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 196],
    [False, 24236],
    [False, 24249],
    [False, 0],
    [False, 0],
    [False, 0]]],
  ['regression: 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]]],
  ['control: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['control: 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]]],
  ['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 12',
   [1000,
    [[True, 53638],
     [True, 11442],
     [False, 11564],
     [True, 24156],
     [False, 44990],
     [True, 45016],
     [True, 539],
     [False, 562],
     [True, 677],
     [True, 8181],
     [True, 18211],
     [False, 18406],
     [True, 18528],
     [True, 18593]]],
   [[False, 0],
    [True, 1000],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [True, 1000],
    [False, 0],
    [False, 0],
    [True, 1000],
    [True, 1000],
    [False, 0],
    [False, 0],
    [False, 65]]],
  ['regression: scenario 26',
   [40000,
    [[False, 62137],
     [True, 62189],
     [True, 62205],
     [True, 3058],
     [True, 3093],
     [True, 3203],
     [True, 3254],
     [False, 3435],
     [False, 3460],
     [True, 3482],
     [True, 3516],
     [True, 3537],
     [False, 3676],
     [True, 22059]]],
   [[False, 0],
    [False, 0],
    [False, 16],
    [False, 6405],
    [False, 6440],
    [False, 6550],
    [False, 6601],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 34],
    [False, 55],
    [False, 0],
    [False, 0]]],
  ['regression: 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]]],
  ['control: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['control: 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]]],
  ['control: 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 13',
   [65535,
    [[True, 49642],
     [True, 49736],
     [True, 12136],
     [False, 12149],
     [False, 22343],
     [True, 34105],
     [True, 34175],
     [True, 49582],
     [False, 8498],
     [True, 10010],
     [True, 10081],
     [True, 10163],
     [True, 38620],
     [True, 62085]]],
   [[False, 0],
    [False, 94],
    [False, 28030],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 70],
    [False, 15477],
    [False, 0],
    [False, 0],
    [False, 71],
    [False, 153],
    [False, 28610],
    [False, 52075]]],
  ['regression: scenario 28',
   [40000,
    [[True, 34331],
     [False, 34410],
     [False, 34523],
     [True, 34686],
     [True, 34828],
     [True, 35005],
     [True, 43248],
     [True, 221]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 142],
    [False, 319],
    [False, 8562],
    [False, 31071]]],
  ['regression: 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]]],
  ['control: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['control: 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]]],
  ['control: 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: clock wrap[[False, 0], [False, 30], [False, -65460], [False, -65436], [False, 0]][[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]Failed
regression: scenario 6[[False, 0], [False, 114], [False, -41464], [False, -41290], [False, -41104], [False, -40998], [False, -40803], [False, -37233], [False, -22652], [False, -59314], [False, -59168], [False, -56795]][[False, 0], [False, 114], [False, 24072], [False, 24246], [False, 24432], [False, 24538], [False, 24733], [False, 28303], [True, 40000], [True, 40000], [True, 40000], [True, 40000]]Failed
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
control: enable after idle[[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]][[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]Passed
regression: scenario 1[[False, 0], [False, 42], [False, -43381], [False, 0], [False, 0], [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: scenario 2[[False, 0], [True, 100], [True, 100], [False, 0], [False, 0], [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]]Passed
control: scenario 3[[False, 0], [False, 0], [False, 0], [False, 4187], [False, 0], [False, 0], [False, 0], [False, 11775], [False, 11911]][[False, 0], [False, 0], [False, 0], [False, 4187], [False, 0], [False, 0], [False, 0], [False, 11775], [False, 11911]]Passed

SHA-256 / cbec1045f2ae5130283e04af934ae6624599f62b629c8b8b78c4faa80b7c205b

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:
            start = None
            done = False
            out.append([False, 0])
            continue
        if start is None:
            start = clock
        elapsed = abs(clock - start)
        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: clock wrap',
   [100, [[True, 65500], [True, 65530], [True, 40], [True, 64], [False, 70]]],
   [[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]],
  ['regression: scenario 6',
   [40000,
    [[True, 63614],
     [True, 63728],
     [True, 22150],
     [True, 22324],
     [True, 22510],
     [True, 22616],
     [True, 22811],
     [True, 26381],
     [True, 40962],
     [True, 4300],
     [True, 4446],
     [True, 6819]]],
   [[False, 0],
    [False, 114],
    [False, 24072],
    [False, 24246],
    [False, 24432],
    [False, 24538],
    [False, 24733],
    [False, 28303],
    [True, 40000],
    [True, 40000],
    [True, 40000],
    [True, 40000]]],
  ['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]]],
  ['control: 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: 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]]],
  ['control: 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]]]],
 [['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 9',
   [65535,
    [[True, 50243],
     [True, 50414],
     [True, 54443],
     [True, 54585],
     [True, 54684],
     [False, 63787],
     [True, 63849],
     [True, 7734]]],
   [[False, 0],
    [False, 171],
    [False, 4200],
    [False, 4342],
    [False, 4441],
    [False, 0],
    [False, 0],
    [False, 9421]]],
  ['regression: 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]]],
  ['control: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['control: 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: 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 5',
   [5,
    [[True, 36141],
     [True, 56668],
     [False, 56831],
     [True, 56893],
     [True, 6106],
     [True, 24708],
     [True, 45326],
     [True, 65076],
     [True, 65184]]],
   [[False, 0], [True, 5], [False, 0], [False, 0], [True, 5], [True, 5], [True, 5], [True, 5], [True, 5]]],
  ['regression: scenario 9',
   [65535,
    [[True, 44901],
     [False, 62429],
     [True, 62596],
     [True, 62792],
     [True, 21296],
     [True, 21309],
     [False, 21419],
     [False, 21455],
     [True, 21477]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 196],
    [False, 24236],
    [False, 24249],
    [False, 0],
    [False, 0],
    [False, 0]]],
  ['regression: 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]]],
  ['control: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['control: 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]]],
  ['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 12',
   [1000,
    [[True, 53638],
     [True, 11442],
     [False, 11564],
     [True, 24156],
     [False, 44990],
     [True, 45016],
     [True, 539],
     [False, 562],
     [True, 677],
     [True, 8181],
     [True, 18211],
     [False, 18406],
     [True, 18528],
     [True, 18593]]],
   [[False, 0],
    [True, 1000],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [True, 1000],
    [False, 0],
    [False, 0],
    [True, 1000],
    [True, 1000],
    [False, 0],
    [False, 0],
    [False, 65]]],
  ['regression: scenario 26',
   [40000,
    [[False, 62137],
     [True, 62189],
     [True, 62205],
     [True, 3058],
     [True, 3093],
     [True, 3203],
     [True, 3254],
     [False, 3435],
     [False, 3460],
     [True, 3482],
     [True, 3516],
     [True, 3537],
     [False, 3676],
     [True, 22059]]],
   [[False, 0],
    [False, 0],
    [False, 16],
    [False, 6405],
    [False, 6440],
    [False, 6550],
    [False, 6601],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 34],
    [False, 55],
    [False, 0],
    [False, 0]]],
  ['regression: 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]]],
  ['control: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['control: 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]]],
  ['control: 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 13',
   [65535,
    [[True, 49642],
     [True, 49736],
     [True, 12136],
     [False, 12149],
     [False, 22343],
     [True, 34105],
     [True, 34175],
     [True, 49582],
     [False, 8498],
     [True, 10010],
     [True, 10081],
     [True, 10163],
     [True, 38620],
     [True, 62085]]],
   [[False, 0],
    [False, 94],
    [False, 28030],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 70],
    [False, 15477],
    [False, 0],
    [False, 0],
    [False, 71],
    [False, 153],
    [False, 28610],
    [False, 52075]]],
  ['regression: scenario 28',
   [40000,
    [[True, 34331],
     [False, 34410],
     [False, 34523],
     [True, 34686],
     [True, 34828],
     [True, 35005],
     [True, 43248],
     [True, 221]]],
   [[False, 0],
    [False, 0],
    [False, 0],
    [False, 0],
    [False, 142],
    [False, 319],
    [False, 8562],
    [False, 31071]]],
  ['regression: 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]]],
  ['control: enable after idle',
   [50, [[False, 0], [False, 400], [True, 900], [True, 930], [True, 960]]],
   [[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]],
  ['control: 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]]],
  ['control: 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: clock wrap[[False, 0], [False, 30], [True, 100], [True, 100], [False, 0]][[False, 0], [False, 30], [False, 76], [True, 100], [False, 0]]Failed
regression: scenario 6[[False, 0], [False, 114], [True, 40000], [True, 40000], [True, 40000], [True, 40000], [True, 40000], [True, 40000], [True, 40000], [True, 40000], [True, 40000], [True, 40000]][[False, 0], [False, 114], [False, 24072], [False, 24246], [False, 24432], [False, 24538], [False, 24733], [False, 28303], [True, 40000], [True, 40000], [True, 40000], [True, 40000]]Failed
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
control: enable after idle[[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]][[False, 0], [False, 0], [False, 0], [False, 30], [True, 50]]Passed
regression: scenario 1[[False, 0], [False, 42], [True, 100], [False, 0], [False, 0], [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]]Passed
control: scenario 2[[False, 0], [True, 100], [True, 100], [False, 0], [False, 0], [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]]Passed
control: scenario 3[[False, 0], [False, 0], [False, 0], [False, 4187], [False, 0], [False, 0], [False, 0], [False, 11775], [False, 11911]][[False, 0], [False, 0], [False, 0], [False, 4187], [False, 0], [False, 0], [False, 0], [False, 11775], [False, 11911]]Passed

SHA-256 / a950e29f8281441ac939797c4211386389b03a3d8b7d12f30ca8380523a425ab

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 2026-09-29T14:51:43.910331+00:00.

Case digest / 1cf6ef2b0a7d3d1a4aa581ad8d64f3ff194a96acd66e35cfa72ab5d9ec941364