FAILURE MAP
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FA-89301 / Digital logic simulation / Open access

Scan test enable not ORed into the latch · case 01

With te=1 and en=0 the gated clock stays low during scan shift.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Test enable is ignored by the gating latch.

THE FAILURE

Test enable is ignored by the gating latch.

Unsuccessful approach: ORing te after the latch makes the output follow te glitchily.

Case contract

Input [samples] of [clk, en, te]. The enable latch starts at 0 and is transparent while clk is 0 (q = en or te), holding while clk is 1. The gated clock is clk and q. Return [gated clock per sample, number of gated rising edges counting from an initial low].

Why this case matters

Integrated clock gating cells rely on a low-transparent latch to avoid glitches; simulation models that skip the latch show clock pulses that silicon never produces.

1 / The failure

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

N = 1
observations = []
def solve(samples):
    q = 0
    g = []
    for clk, en, te in samples:
        if clk == 0:
            q = int(en)
        g.append(int(clk == 1 and q == 1))
    edges = sum(1 for a, b in zip([0] + g, g) if a == 0 and b == 1)
    return [g, edges]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1], 2]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 0, 0], [1, 0, 0]]], [[0, 0, 1, 0, 0], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1], 2])], [('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1, 0, 1], 3]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 1], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1, 0, 1], 3])], [('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1], 4]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 0, 0], [1, 0, 0]]], [[0, 0, 1, 0, 0], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1, 0, 1, 0, 1], 4])], [('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1], 5]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 1], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1, 0, 1, 0, 1, 0, 1], 5])], [('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1], 6]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 0, 0], [1, 0, 0]]], [[0, 0, 1, 0, 0], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1], 6])]]
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
enable drops while clock high[[0, 1, 1, 0, 0], 1][[0, 1, 1, 0, 0], 1]Passed
enable rises while clock high[[0, 0, 0, 0, 1, 0, 1], 2][[0, 0, 0, 0, 1, 0, 1], 2]Passed
test enable forces clock[[0, 0, 0, 0], 0][[0, 1, 0, 0], 1]Failed
starts with clock high[[0, 0, 1, 0, 0], 1][[0, 0, 1, 0, 0], 1]Passed
test enable drops mid pulse[[0, 0, 0, 0], 0][[0, 1, 1, 0], 1]Failed
steady enable[[0, 1, 0, 1], 2][[0, 1, 0, 1], 2]Passed

SHA-256 / bb2122b0a2bc98dca536a109be07eb025262c5e2ab93a30e2a7c8c3ed53e7fe3

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(samples):
    q = 0
    g = []
    for clk, en, te in samples:
        if clk == 0:
            q = int(en)
        g.append(int(clk == 1 and (q == 1 or te == 1)))
    edges = sum(1 for a, b in zip([0] + g, g) if a == 0 and b == 1)
    return [g, edges]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1], 2]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 0, 0], [1, 0, 0]]], [[0, 0, 1, 0, 0], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1], 2])], [('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1, 0, 1], 3]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 1], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1, 0, 1], 3])], [('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1], 4]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 0, 0], [1, 0, 0]]], [[0, 0, 1, 0, 0], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1, 0, 1, 0, 1], 4])], [('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1], 5]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 1], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1, 0, 1, 0, 1, 0, 1], 5])], [('enable drops while clock high', [[[0, 1, 0], [1, 1, 0], [1, 0, 0], [0, 0, 0], [1, 0, 0]]], [[0, 1, 1, 0, 0], 1]), ('enable rises while clock high', [[[0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1], 6]), ('test enable forces clock', [[[0, 0, 1], [1, 0, 1], [0, 0, 0], [1, 0, 0]]], [[0, 1, 0, 0], 1]), ('starts with clock high', [[[1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 0, 0], [1, 0, 0]]], [[0, 0, 1, 0, 0], 1]), ('test enable drops mid pulse', [[[0, 0, 1], [1, 0, 1], [1, 0, 0], [0, 0, 0]]], [[0, 1, 1, 0], 1]), ('steady enable', [[[0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0], [0, 1, 0], [1, 1, 0]]], [[0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1], 6])]]
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
enable drops while clock high[[0, 1, 1, 0, 0], 1][[0, 1, 1, 0, 0], 1]Passed
enable rises while clock high[[0, 0, 0, 0, 1, 0, 1], 2][[0, 0, 0, 0, 1, 0, 1], 2]Passed
test enable forces clock[[0, 1, 0, 0], 1][[0, 1, 0, 0], 1]Passed
starts with clock high[[0, 0, 1, 0, 0], 1][[0, 0, 1, 0, 0], 1]Passed
test enable drops mid pulse[[0, 1, 0, 0], 1][[0, 1, 1, 0], 1]Failed
steady enable[[0, 1, 0, 1], 2][[0, 1, 0, 1], 2]Passed

SHA-256 / ddcfceac6cd2a0f034a1b6ffe902136d62636b19e35be8a9fe94418b979ba68b

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 6 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.

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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 2026-09-29T14:51:16.202109+00:00.

Case digest / fc19091d101a621aee3f983b41b6c8320ad2b65d9d984124f07b648fb3604fad