FAILURE MAP
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FA-92081 / PLC ladder logic scan cycles / Open access

Sequencer wraps to the home element instead of step 1 · case 01

After the last step the machine outputs the home pattern and needs an extra advance before step 1.

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

ROOT CAUSE

The wrap assigns position 0.

THE FAILURE

The wrap assigns position 0.

Unsuccessful approach: Computing the wrap as position modulo length breaks a two-element file.

Case contract

Sequencer output (SQO). words is the sequencer file whose element 0 is the home step; position starts at 0. On each rising edge of enable the position advances; past the last element it wraps to 1 (not 0). Each advance writes dest = (dest AND NOT mask) OR (word AND mask) in 16 bits. A reset input returns position to 0 without writing dest and has priority over a coincident advance; the enable edge memory is always updated. steps is a list of [enable, reset]; return [position, dest] per scan.

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(words, mask, start_dest, steps):
    pos = 0
    dest = start_dest
    prev = False
    length = len(words) - 1
    out = []
    for en, res in steps:
        en = bool(en)
        if res:
            pos = 0
        elif en and not prev:
            pos += 1
            if pos > length:
                pos = 0
            dest = (dest & ~mask & 0xFFFF) | (words[pos] & mask)
        prev = en
        out.append([pos, dest])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['control: scenario 1',
   [[26918, 50611, 8879, 59828],
    65535,
    52597,
    [[False, False],
     [False, False],
     [False, False],
     [True, True],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False]]],
   [[0, 52597],
    [0, 52597],
    [0, 52597],
    [0, 52597],
    [0, 52597],
    [0, 52597],
    [0, 52597],
    [1, 50611],
    [1, 50611],
    [1, 50611]]],
  ['control: scenario 2',
   [[42968, 29173, 43546],
    255,
    5794,
    [[True, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [False, False],
     [False, False],
     [False, False],
     [True, True],
     [False, False]]],
   [[1, 5877],
    [1, 5877],
    [1, 5877],
    [1, 5877],
    [2, 5658],
    [2, 5658],
    [2, 5658],
    [2, 5658],
    [0, 5658],
    [0, 5658]]],
  ['control: scenario 3',
   [[16785, 47110, 21847, 45361],
    61440,
    41889,
    [[True, False],
     [True, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False]]],
   [[1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985]]],
  ['control: scenario 4',
   [[26660, 61415, 54040],
    65535,
    45106,
    [[True, False], [True, False], [True, False], [False, False], [False, False], [True, False]]],
   [[1, 61415], [1, 61415], [1, 61415], [1, 61415], [1, 61415], [2, 54040]]]],
 [['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['regression: scenario 7',
   [[52955, 10653],
    61440,
    49142,
    [[False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False]]],
   [[0, 49142],
    [0, 49142],
    [0, 49142],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278]]],
  ['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['regression: scenario 1',
   [[8488, 43469, 38296, 4034],
    255,
    44563,
    [[False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False]]],
   [[0, 44563],
    [1, 44749],
    [1, 44749],
    [1, 44749],
    [1, 44749],
    [2, 44696],
    [2, 44696],
    [3, 44738],
    [3, 44738],
    [1, 44749],
    [1, 44749],
    [2, 44696]]],
  ['control: scenario 2',
   [[43079, 20640, 23622, 26553],
    255,
    15109,
    [[False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [False, True]]],
   [[0, 15109],
    [0, 15109],
    [1, 15264],
    [1, 15264],
    [1, 15264],
    [1, 15264],
    [2, 15174],
    [2, 15174],
    [2, 15174],
    [2, 15174],
    [3, 15289],
    [0, 15289]]],
  ['control: scenario 3',
   [[16618, 36272, 41924, 55813],
    3855,
    48911,
    [[True, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [False, False]]],
   [[1, 48384], [1, 48384], [1, 48384], [1, 48384], [1, 48384], [2, 45828], [2, 45828]]]],
 [['regression: scenario 2',
   [[36741, 30504],
    65535,
    26589,
    [[True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [False, False],
     [True, True],
     [True, False],
     [False, False]]],
   [[1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [0, 30504],
    [0, 30504],
    [0, 30504]]],
  ['regression: scenario 18',
   [[6005, 39810],
    255,
    1846,
    [[False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, True],
     [False, False]]],
   [[0, 1846],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [0, 1922],
    [0, 1922]]],
  ['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['control: scenario 1',
   [[38610, 2229],
    65535,
    14704,
    [[False, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, True],
     [False, False]]],
   [[0, 14704], [0, 14704], [0, 14704], [0, 14704], [0, 14704], [1, 2229], [1, 2229], [0, 2229], [0, 2229]]],
  ['control: scenario 3',
   [[45414, 65173, 31151, 4829],
    3855,
    46402,
    [[False, True],
     [False, False],
     [True, True],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False]]],
   [[0, 46402],
    [0, 46402],
    [0, 46402],
    [0, 46402],
    [0, 46402],
    [0, 46402],
    [1, 48709],
    [1, 48709],
    [1, 48709]]]],
 [['regression: scenario 2',
   [[57902, 51779],
    61440,
    26811,
    [[True, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False]]],
   [[1, 51387], [1, 51387], [1, 51387], [1, 51387], [1, 51387], [1, 51387], [1, 51387], [1, 51387]]],
  ['regression: scenario 20',
   [[9876, 56752],
    255,
    50114,
    [[False, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False]]],
   [[0, 50114],
    [0, 50114],
    [0, 50114],
    [0, 50114],
    [0, 50114],
    [0, 50114],
    [1, 50096],
    [1, 50096],
    [1, 50096],
    [1, 50096],
    [1, 50096],
    [1, 50096]]],
  ['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['regression: scenario 1',
   [[61786, 58708],
    255,
    45362,
    [[False, False],
     [False, False],
     [False, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False]]],
   [[0, 45362], [0, 45362], [0, 45362], [1, 45396], [1, 45396], [1, 45396], [1, 45396]]],
  ['control: scenario 3',
   [[35305, 48952, 41314, 29239, 28773],
    65535,
    11028,
    [[False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [True, True]]],
   [[0, 11028],
    [0, 11028],
    [1, 48952],
    [1, 48952],
    [1, 48952],
    [1, 48952],
    [2, 41314],
    [2, 41314],
    [2, 41314],
    [2, 41314],
    [2, 41314],
    [0, 41314]]]],
 [['regression: scenario 15',
   [[10064, 26257],
    255,
    24919,
    [[True, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, True],
     [True, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False]]],
   [[1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [0, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977]]],
  ['regression: scenario 21',
   [[12086, 47767],
    65535,
    46065,
    [[False, False],
     [False, False],
     [True, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, True],
     [True, True],
     [True, False],
     [False, False],
     [False, False]]],
   [[0, 46065],
    [0, 46065],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [0, 47767],
    [0, 47767],
    [0, 47767],
    [0, 47767],
    [0, 47767]]],
  ['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['regression: scenario 1',
   [[39974, 26951],
    3855,
    4546,
    [[False, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, True]]],
   [[0, 4546],
    [0, 4546],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [0, 6599]]],
  ['control: scenario 2',
   [[43067, 57880, 6921, 33106, 51712],
    255,
    13830,
    [[True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, True],
     [True, True],
     [False, False],
     [True, False],
     [False, False]]],
   [[1, 13848],
    [1, 13848],
    [1, 13848],
    [2, 13833],
    [2, 13833],
    [2, 13833],
    [3, 13906],
    [3, 13906],
    [0, 13906],
    [0, 13906],
    [0, 13906],
    [1, 13848],
    [1, 13848]]]]]
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: wrap past last step[[1, 43793], [1, 43793], [2, 43810], [2, 43810], [0, 43776], [0, 43776]][[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]Failed
regression: two element file[[1, 9], [1, 9], [0, 5], [0, 5], [1, 9]][[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]Failed
control: reset while enabled[[1, 65523], [0, 65523], [0, 65523], [1, 65523]][[1, 65523], [0, 65523], [0, 65523], [1, 65523]]Passed
control: reset with advance[[0, 170], [0, 170], [0, 170], [1, 426]][[0, 170], [0, 170], [0, 170], [1, 426]]Passed
control: scenario 1[[0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [1, 50611], [1, 50611], [1, 50611]][[0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [1, 50611], [1, 50611], [1, 50611]]Passed
control: scenario 2[[1, 5877], [1, 5877], [1, 5877], [1, 5877], [2, 5658], [2, 5658], [2, 5658], [2, 5658], [0, 5658], [0, 5658]][[1, 5877], [1, 5877], [1, 5877], [1, 5877], [2, 5658], [2, 5658], [2, 5658], [2, 5658], [0, 5658], [0, 5658]]Passed
control: scenario 3[[1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985]][[1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985]]Passed
control: scenario 4[[1, 61415], [1, 61415], [1, 61415], [1, 61415], [1, 61415], [2, 54040]][[1, 61415], [1, 61415], [1, 61415], [1, 61415], [1, 61415], [2, 54040]]Passed

SHA-256 / f1a8c7e2820a06916e3a9b06dcb43c02feb58fe07553b5037dc43cdea2e20c80

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(words, mask, start_dest, steps):
    pos = 0
    dest = start_dest
    prev = False
    length = len(words) - 1
    out = []
    for en, res in steps:
        en = bool(en)
        if res:
            pos = 0
        elif en and not prev:
            pos += 1
            if pos > length:
                pos = pos % length
            dest = (dest & ~mask & 0xFFFF) | (words[pos] & mask)
        prev = en
        out.append([pos, dest])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['control: scenario 1',
   [[26918, 50611, 8879, 59828],
    65535,
    52597,
    [[False, False],
     [False, False],
     [False, False],
     [True, True],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False]]],
   [[0, 52597],
    [0, 52597],
    [0, 52597],
    [0, 52597],
    [0, 52597],
    [0, 52597],
    [0, 52597],
    [1, 50611],
    [1, 50611],
    [1, 50611]]],
  ['control: scenario 2',
   [[42968, 29173, 43546],
    255,
    5794,
    [[True, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [False, False],
     [False, False],
     [False, False],
     [True, True],
     [False, False]]],
   [[1, 5877],
    [1, 5877],
    [1, 5877],
    [1, 5877],
    [2, 5658],
    [2, 5658],
    [2, 5658],
    [2, 5658],
    [0, 5658],
    [0, 5658]]],
  ['control: scenario 3',
   [[16785, 47110, 21847, 45361],
    61440,
    41889,
    [[True, False],
     [True, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False]]],
   [[1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985]]],
  ['control: scenario 4',
   [[26660, 61415, 54040],
    65535,
    45106,
    [[True, False], [True, False], [True, False], [False, False], [False, False], [True, False]]],
   [[1, 61415], [1, 61415], [1, 61415], [1, 61415], [1, 61415], [2, 54040]]]],
 [['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['regression: scenario 7',
   [[52955, 10653],
    61440,
    49142,
    [[False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False]]],
   [[0, 49142],
    [0, 49142],
    [0, 49142],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278],
    [1, 12278]]],
  ['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['regression: scenario 1',
   [[8488, 43469, 38296, 4034],
    255,
    44563,
    [[False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False]]],
   [[0, 44563],
    [1, 44749],
    [1, 44749],
    [1, 44749],
    [1, 44749],
    [2, 44696],
    [2, 44696],
    [3, 44738],
    [3, 44738],
    [1, 44749],
    [1, 44749],
    [2, 44696]]],
  ['control: scenario 2',
   [[43079, 20640, 23622, 26553],
    255,
    15109,
    [[False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [False, True]]],
   [[0, 15109],
    [0, 15109],
    [1, 15264],
    [1, 15264],
    [1, 15264],
    [1, 15264],
    [2, 15174],
    [2, 15174],
    [2, 15174],
    [2, 15174],
    [3, 15289],
    [0, 15289]]],
  ['control: scenario 3',
   [[16618, 36272, 41924, 55813],
    3855,
    48911,
    [[True, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [False, False]]],
   [[1, 48384], [1, 48384], [1, 48384], [1, 48384], [1, 48384], [2, 45828], [2, 45828]]]],
 [['regression: scenario 2',
   [[36741, 30504],
    65535,
    26589,
    [[True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [False, False],
     [True, True],
     [True, False],
     [False, False]]],
   [[1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [1, 30504],
    [0, 30504],
    [0, 30504],
    [0, 30504]]],
  ['regression: scenario 18',
   [[6005, 39810],
    255,
    1846,
    [[False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, True],
     [False, False]]],
   [[0, 1846],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [1, 1922],
    [0, 1922],
    [0, 1922]]],
  ['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['control: scenario 1',
   [[38610, 2229],
    65535,
    14704,
    [[False, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, True],
     [False, False]]],
   [[0, 14704], [0, 14704], [0, 14704], [0, 14704], [0, 14704], [1, 2229], [1, 2229], [0, 2229], [0, 2229]]],
  ['control: scenario 3',
   [[45414, 65173, 31151, 4829],
    3855,
    46402,
    [[False, True],
     [False, False],
     [True, True],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False]]],
   [[0, 46402],
    [0, 46402],
    [0, 46402],
    [0, 46402],
    [0, 46402],
    [0, 46402],
    [1, 48709],
    [1, 48709],
    [1, 48709]]]],
 [['regression: scenario 2',
   [[57902, 51779],
    61440,
    26811,
    [[True, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False]]],
   [[1, 51387], [1, 51387], [1, 51387], [1, 51387], [1, 51387], [1, 51387], [1, 51387], [1, 51387]]],
  ['regression: scenario 20',
   [[9876, 56752],
    255,
    50114,
    [[False, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False]]],
   [[0, 50114],
    [0, 50114],
    [0, 50114],
    [0, 50114],
    [0, 50114],
    [0, 50114],
    [1, 50096],
    [1, 50096],
    [1, 50096],
    [1, 50096],
    [1, 50096],
    [1, 50096]]],
  ['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['regression: scenario 1',
   [[61786, 58708],
    255,
    45362,
    [[False, False],
     [False, False],
     [False, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False]]],
   [[0, 45362], [0, 45362], [0, 45362], [1, 45396], [1, 45396], [1, 45396], [1, 45396]]],
  ['control: scenario 3',
   [[35305, 48952, 41314, 29239, 28773],
    65535,
    11028,
    [[False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False],
     [True, False],
     [False, False],
     [True, True]]],
   [[0, 11028],
    [0, 11028],
    [1, 48952],
    [1, 48952],
    [1, 48952],
    [1, 48952],
    [2, 41314],
    [2, 41314],
    [2, 41314],
    [2, 41314],
    [2, 41314],
    [0, 41314]]]],
 [['regression: scenario 15',
   [[10064, 26257],
    255,
    24919,
    [[True, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, False],
     [False, True],
     [True, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False]]],
   [[1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [0, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977],
    [1, 24977]]],
  ['regression: scenario 21',
   [[12086, 47767],
    65535,
    46065,
    [[False, False],
     [False, False],
     [True, False],
     [False, False],
     [False, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [True, True],
     [True, True],
     [True, False],
     [False, False],
     [False, False]]],
   [[0, 46065],
    [0, 46065],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [1, 47767],
    [0, 47767],
    [0, 47767],
    [0, 47767],
    [0, 47767],
    [0, 47767]]],
  ['regression: wrap past last step',
   [[0, 17, 34],
    255,
    43776,
    [[True, False], [False, False], [True, False], [False, False], [True, False], [True, False]]],
   [[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]],
  ['regression: two element file',
   [[5, 9], 65535, 0, [[True, False], [False, False], [True, False], [False, False], [True, False]]],
   [[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]],
  ['control: reset while enabled',
   [[0, 3, 12], 15, 65520, [[True, False], [True, True], [False, False], [True, False]]],
   [[1, 65523], [0, 65523], [0, 65523], [1, 65523]]],
  ['control: reset with advance',
   [[0, 256, 512], 65280, 170, [[False, False], [True, True], [False, False], [True, False]]],
   [[0, 170], [0, 170], [0, 170], [1, 426]]],
  ['regression: scenario 1',
   [[39974, 26951],
    3855,
    4546,
    [[False, False],
     [False, False],
     [True, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, True]]],
   [[0, 4546],
    [0, 4546],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [1, 6599],
    [0, 6599]]],
  ['control: scenario 2',
   [[43067, 57880, 6921, 33106, 51712],
    255,
    13830,
    [[True, False],
     [False, False],
     [False, False],
     [True, False],
     [True, False],
     [False, False],
     [True, False],
     [False, False],
     [True, True],
     [True, True],
     [False, False],
     [True, False],
     [False, False]]],
   [[1, 13848],
    [1, 13848],
    [1, 13848],
    [2, 13833],
    [2, 13833],
    [2, 13833],
    [3, 13906],
    [3, 13906],
    [0, 13906],
    [0, 13906],
    [0, 13906],
    [1, 13848],
    [1, 13848]]]]]
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: wrap past last step[[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]][[1, 43793], [1, 43793], [2, 43810], [2, 43810], [1, 43793], [1, 43793]]Passed
regression: two element file[[1, 9], [1, 9], [0, 5], [0, 5], [1, 9]][[1, 9], [1, 9], [1, 9], [1, 9], [1, 9]]Failed
control: reset while enabled[[1, 65523], [0, 65523], [0, 65523], [1, 65523]][[1, 65523], [0, 65523], [0, 65523], [1, 65523]]Passed
control: reset with advance[[0, 170], [0, 170], [0, 170], [1, 426]][[0, 170], [0, 170], [0, 170], [1, 426]]Passed
control: scenario 1[[0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [1, 50611], [1, 50611], [1, 50611]][[0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [0, 52597], [1, 50611], [1, 50611], [1, 50611]]Passed
control: scenario 2[[1, 5877], [1, 5877], [1, 5877], [1, 5877], [2, 5658], [2, 5658], [2, 5658], [2, 5658], [0, 5658], [0, 5658]][[1, 5877], [1, 5877], [1, 5877], [1, 5877], [2, 5658], [2, 5658], [2, 5658], [2, 5658], [0, 5658], [0, 5658]]Passed
control: scenario 3[[1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985]][[1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985], [1, 45985]]Passed
control: scenario 4[[1, 61415], [1, 61415], [1, 61415], [1, 61415], [1, 61415], [2, 54040]][[1, 61415], [1, 61415], [1, 61415], [1, 61415], [1, 61415], [2, 54040]]Passed

SHA-256 / fd72f02480fb23135c76afd87f85010af2548df2005084cdf770219d1a120fc9

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 2026-09-29T14:51:42.336089+00:00.

Case digest / 06a12ae86f40b30821d4785f5a75a9910428cdb16405d602cf81cdbebb5f1292