FA-89076 / Digital logic simulation / Open access

Only 0 to 1 counted as a rising edge · case 01

Rising transitions through unknown values (0->x, x->1, z->1) do not trigger posedge.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Posedge detection is limited to a literal 0->1 change.

THE FAILURE

Posedge detection is limited to a literal 0->1 change.

Unsuccessful approach: Requiring the destination to be 1 still ignores 0->x and 0->z.

Case contract

Input [seq]: a string of samples over '0','1','x','z'. Levels order 0 < {x,z} < 1 (x and z are the same middle level). A change to a higher level is a posedge (0->1, 0->x, 0->z, x->1, z->1), to a lower level a negedge; x<->z is no edge. The first sample has no predecessor. Return [posedge indices, negedge indices].

Why this case matters

Event controls on clocks and resets fire on unknown transitions; an edge classifier that only knows 0->1 misses or invents triggers.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(*args):
    seq = args[0]
    lvl = {'0': 0, '1': 2}
    pos, neg = [], []
    prev = None
    for i, b in enumerate(seq):
        a, prev = prev, b
        if a is None or a == b:
            continue
        la, lb = lvl.get(a, 1), lvl.get(b, 1)
        if (a, b) == ('0', '1'):
            pos.append(i)
        elif la > lb:
            neg.append(i)
    return [pos, neg]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('plain binary toggles', ['010110'], [[1, 3], [2, 5]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xzx1z'], [[3], [4]]), ('floating rising and falling', ['z1z0z'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xz0'], [[], [1, 3]]), ('starts high without a predecessor', ['110'], [[], [2]]), ('low through unknown to high', ['0x1x0'], [[1, 2], [3, 4]])], [('plain binary toggles', ['0101110'], [[1, 3], [2, 6]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xxzx1z'], [[4], [5]]), ('floating rising and falling', ['z1z0zz'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xxz0'], [[], [1, 4]]), ('starts high without a predecessor', ['1100'], [[], [2]]), ('low through unknown to high', ['00x1x0'], [[2, 3], [4, 5]])], [('plain binary toggles', ['01011110'], [[1, 3], [2, 7]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xxxzx1z'], [[5], [6]]), ('floating rising and falling', ['z1z0zzz'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xxxz0'], [[], [1, 5]]), ('starts high without a predecessor', ['11000'], [[], [2]]), ('low through unknown to high', ['000x1x0'], [[3, 4], [5, 6]])], [('plain binary toggles', ['010111110'], [[1, 3], [2, 8]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xxxxzx1z'], [[6], [7]]), ('floating rising and falling', ['z1z0zzzz'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xxxxz0'], [[], [1, 6]]), ('starts high without a predecessor', ['110000'], [[], [2]]), ('low through unknown to high', ['0000x1x0'], [[4, 5], [6, 7]])], [('plain binary toggles', ['0101111110'], [[1, 3], [2, 9]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xxxxxzx1z'], [[7], [8]]), ('floating rising and falling', ['z1z0zzzzz'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xxxxxz0'], [[], [1, 7]]), ('starts high without a predecessor', ['1100000'], [[], [2]]), ('low through unknown to high', ['00000x1x0'], [[5, 6], [7, 8]])]]
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 fixture	Actual	Expected	Outcome
plain binary toggles	`[[1, 3], [2, 5]]`	`[[1, 3], [2, 5]]`	Passed
edges through unknown and floating	`[[], [3, 4]]`	`[[1, 2], [3, 4]]`	Failed
unknown to floating is no edge	`[[], [4]]`	`[[3], [4]]`	Failed
floating rising and falling	`[[], [2, 3]]`	`[[1, 4], [2, 3]]`	Failed
high to floating then low	`[[], [1, 3]]`	`[[], [1, 3]]`	Passed
starts high without a predecessor	`[[], [2]]`	`[[], [2]]`	Passed
low through unknown to high	`[[], [3, 4]]`	`[[1, 2], [3, 4]]`	Failed

SHA-256 / ff0ff8922384b49a9259e8fb8c78a683d14f40e1663101e0e55e9c3d1c7be176

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(*args):
    seq = args[0]
    lvl = {'0': 0, '1': 2}
    pos, neg = [], []
    prev = None
    for i, b in enumerate(seq):
        a, prev = prev, b
        if a is None or a == b:
            continue
        la, lb = lvl.get(a, 1), lvl.get(b, 1)
        if la < lb and b == '1':
            pos.append(i)
        elif la > lb:
            neg.append(i)
    return [pos, neg]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('plain binary toggles', ['010110'], [[1, 3], [2, 5]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xzx1z'], [[3], [4]]), ('floating rising and falling', ['z1z0z'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xz0'], [[], [1, 3]]), ('starts high without a predecessor', ['110'], [[], [2]]), ('low through unknown to high', ['0x1x0'], [[1, 2], [3, 4]])], [('plain binary toggles', ['0101110'], [[1, 3], [2, 6]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xxzx1z'], [[4], [5]]), ('floating rising and falling', ['z1z0zz'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xxz0'], [[], [1, 4]]), ('starts high without a predecessor', ['1100'], [[], [2]]), ('low through unknown to high', ['00x1x0'], [[2, 3], [4, 5]])], [('plain binary toggles', ['01011110'], [[1, 3], [2, 7]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xxxzx1z'], [[5], [6]]), ('floating rising and falling', ['z1z0zzz'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xxxz0'], [[], [1, 5]]), ('starts high without a predecessor', ['11000'], [[], [2]]), ('low through unknown to high', ['000x1x0'], [[3, 4], [5, 6]])], [('plain binary toggles', ['010111110'], [[1, 3], [2, 8]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xxxxzx1z'], [[6], [7]]), ('floating rising and falling', ['z1z0zzzz'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xxxxz0'], [[], [1, 6]]), ('starts high without a predecessor', ['110000'], [[], [2]]), ('low through unknown to high', ['0000x1x0'], [[4, 5], [6, 7]])], [('plain binary toggles', ['0101111110'], [[1, 3], [2, 9]]), ('edges through unknown and floating', ['0x1z0'], [[1, 2], [3, 4]]), ('unknown to floating is no edge', ['xxxxxzx1z'], [[7], [8]]), ('floating rising and falling', ['z1z0zzzzz'], [[1, 4], [2, 3]]), ('high to floating then low', ['1xxxxxz0'], [[], [1, 7]]), ('starts high without a predecessor', ['1100000'], [[], [2]]), ('low through unknown to high', ['00000x1x0'], [[5, 6], [7, 8]])]]
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 fixture	Actual	Expected	Outcome
plain binary toggles	`[[1, 3], [2, 5]]`	`[[1, 3], [2, 5]]`	Passed
edges through unknown and floating	`[[2], [3, 4]]`	`[[1, 2], [3, 4]]`	Failed
unknown to floating is no edge	`[[3], [4]]`	`[[3], [4]]`	Passed
floating rising and falling	`[[1], [2, 3]]`	`[[1, 4], [2, 3]]`	Failed
high to floating then low	`[[], [1, 3]]`	`[[], [1, 3]]`	Passed
starts high without a predecessor	`[[], [2]]`	`[[], [2]]`	Passed
low through unknown to high	`[[2], [3, 4]]`	`[[1, 2], [3, 4]]`	Failed

SHA-256 / 7bf177e0ad18552b0a916d3ee2dd5cb75159d9d0d4d3d9b8e7e1e0eaf1e15f1c

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 7 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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

A deterministic bounded teaching model of one simulator rule set; the contract is stipulated and is not a claim of conformance to any HDL standard or commercial simulator. 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 2026-09-29T14:51:14.127880+00:00.

Case digest / 475c93aebab698323d8ded31c5d032dd30e059b55407347da1277f01b32a200d