FAILURE MAP
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FA-88886 / Digital logic simulation / Open access

Output events pending after the last stimulus are lost · case 01

The final output transition is missing whenever it matures after the last input change.

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

ROOT CAUSE

The event loop ends with the last input change and never drains the pending queue.

VERIFIED REPAIR

Append a far-future sentinel so every pending output event matures before returning.

Unsuccessful approach: A sentinel at the time of the last input only drains events that have already matured.

Case contract

Input [gate, rise_delay, fall_delay, v0, events]; gate is 'buf' or 'not', events are time-sorted [t, v] input changes. Output starts at f(v0) (not reported). Each input change schedules f(v) at t + rise_delay when f(v)==1 else t + fall_delay, and cancels every pending output event (inertial delay). Pending events maturing at or before the next input time are committed first. Report [time, value] only when the output value changes; all pending events are committed after the last input.

Why this case matters

Event-driven simulators filter pulses narrower than a gate delay; getting cancellation, polarity and flushing right determines the waveform.

1 / The failure

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

N = 1
observations = []
def solve(*args):
    gate, dr, df, v0, events = args
    f = (lambda v: 1 - v) if gate == 'not' else (lambda v: v)
    out = f(v0)
    q = []
    res = []
    for t, v in events:
        while q and q[0][0] <= t:
            at, nv = q.pop(0)
            if nv != out:
                out = nv
                res.append([at, nv])
        if v is None:
            break
        q.clear()
        nv = f(v)
        q.append([t + (dr if nv == 1 else df), nv])
    return res
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('pulse shorter than inertial delay is filtered', ['buf', 4, 4, 0, [[10, 1], [12, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [21, 0]]], [[12, 1], [25, 0]]), ('inverter uses output polarity for delay', ['not', 2, 6, 0, [[10, 1], [30, 0]]], [[16, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [10, 0]]], [[12, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[1, 1]]], [[5, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [21, 0]]], [[25, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [41, 1]]], [[15, 1], [20, 0], [46, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 5, 5, 0, [[10, 1], [13, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [22, 0]]], [[12, 1], [26, 0]]), ('inverter uses output polarity for delay', ['not', 2, 7, 0, [[10, 1], [30, 0]]], [[17, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [11, 0]]], [[13, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[2, 1]]], [[6, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [22, 0]]], [[26, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [42, 1]]], [[15, 1], [20, 0], [47, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 6, 6, 0, [[10, 1], [14, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [23, 0]]], [[12, 1], [27, 0]]), ('inverter uses output polarity for delay', ['not', 2, 8, 0, [[10, 1], [30, 0]]], [[18, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [12, 0]]], [[14, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[3, 1]]], [[7, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [23, 0]]], [[27, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [43, 1]]], [[15, 1], [20, 0], [48, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 7, 7, 0, [[10, 1], [15, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [24, 0]]], [[12, 1], [28, 0]]), ('inverter uses output polarity for delay', ['not', 2, 9, 0, [[10, 1], [30, 0]]], [[19, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [13, 0]]], [[15, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[4, 1]]], [[8, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [24, 0]]], [[28, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [44, 1]]], [[15, 1], [20, 0], [49, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 8, 8, 0, [[10, 1], [16, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [25, 0]]], [[12, 1], [29, 0]]), ('inverter uses output polarity for delay', ['not', 2, 10, 0, [[10, 1], [30, 0]]], [[20, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [14, 0]]], [[16, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[5, 1]]], [[9, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [25, 0]]], [[29, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [45, 1]]], [[15, 1], [20, 0], [50, 1]])]]
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
pulse shorter than inertial delay is filtered[][]Passed
wide pulse passes with rise and fall delays[[12, 1]][[12, 1], [25, 0]]Failed
inverter uses output polarity for delay[[16, 0]][[16, 0], [32, 1]]Failed
redundant input event produces no output edge[][[12, 0]]Failed
final pending event is committed[][[5, 1]]Failed
inverter glitch cancelled[][[25, 1]]Failed
output matures exactly at next input change[[15, 1], [20, 0]][[15, 1], [20, 0], [46, 1]]Failed

SHA-256 / a662a64935611bfc13c0da4195c2405f1f284497607ca9940fcde20d1e1d73ce

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(*args):
    gate, dr, df, v0, events = args
    f = (lambda v: 1 - v) if gate == 'not' else (lambda v: v)
    out = f(v0)
    q = []
    res = []
    for t, v in events + [[events[-1][0], None]]:
        while q and q[0][0] <= t:
            at, nv = q.pop(0)
            if nv != out:
                out = nv
                res.append([at, nv])
        if v is None:
            break
        q.clear()
        nv = f(v)
        q.append([t + (dr if nv == 1 else df), nv])
    return res
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('pulse shorter than inertial delay is filtered', ['buf', 4, 4, 0, [[10, 1], [12, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [21, 0]]], [[12, 1], [25, 0]]), ('inverter uses output polarity for delay', ['not', 2, 6, 0, [[10, 1], [30, 0]]], [[16, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [10, 0]]], [[12, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[1, 1]]], [[5, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [21, 0]]], [[25, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [41, 1]]], [[15, 1], [20, 0], [46, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 5, 5, 0, [[10, 1], [13, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [22, 0]]], [[12, 1], [26, 0]]), ('inverter uses output polarity for delay', ['not', 2, 7, 0, [[10, 1], [30, 0]]], [[17, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [11, 0]]], [[13, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[2, 1]]], [[6, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [22, 0]]], [[26, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [42, 1]]], [[15, 1], [20, 0], [47, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 6, 6, 0, [[10, 1], [14, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [23, 0]]], [[12, 1], [27, 0]]), ('inverter uses output polarity for delay', ['not', 2, 8, 0, [[10, 1], [30, 0]]], [[18, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [12, 0]]], [[14, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[3, 1]]], [[7, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [23, 0]]], [[27, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [43, 1]]], [[15, 1], [20, 0], [48, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 7, 7, 0, [[10, 1], [15, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [24, 0]]], [[12, 1], [28, 0]]), ('inverter uses output polarity for delay', ['not', 2, 9, 0, [[10, 1], [30, 0]]], [[19, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [13, 0]]], [[15, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[4, 1]]], [[8, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [24, 0]]], [[28, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [44, 1]]], [[15, 1], [20, 0], [49, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 8, 8, 0, [[10, 1], [16, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [25, 0]]], [[12, 1], [29, 0]]), ('inverter uses output polarity for delay', ['not', 2, 10, 0, [[10, 1], [30, 0]]], [[20, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [14, 0]]], [[16, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[5, 1]]], [[9, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [25, 0]]], [[29, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [45, 1]]], [[15, 1], [20, 0], [50, 1]])]]
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
pulse shorter than inertial delay is filtered[][]Passed
wide pulse passes with rise and fall delays[[12, 1]][[12, 1], [25, 0]]Failed
inverter uses output polarity for delay[[16, 0]][[16, 0], [32, 1]]Failed
redundant input event produces no output edge[][[12, 0]]Failed
final pending event is committed[][[5, 1]]Failed
inverter glitch cancelled[][[25, 1]]Failed
output matures exactly at next input change[[15, 1], [20, 0]][[15, 1], [20, 0], [46, 1]]Failed

SHA-256 / dfefc22cb90318c0fb9a21b3bc8729d2a72e0758c5d0c4525579548e7369d594

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(*args):
    gate, dr, df, v0, events = args
    f = (lambda v: 1 - v) if gate == 'not' else (lambda v: v)
    out = f(v0)
    q = []
    res = []
    for t, v in events + [[10 ** 9, None]]:
        while q and q[0][0] <= t:
            at, nv = q.pop(0)
            if nv != out:
                out = nv
                res.append([at, nv])
        if v is None:
            break
        q.clear()
        nv = f(v)
        q.append([t + (dr if nv == 1 else df), nv])
    return res
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('pulse shorter than inertial delay is filtered', ['buf', 4, 4, 0, [[10, 1], [12, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [21, 0]]], [[12, 1], [25, 0]]), ('inverter uses output polarity for delay', ['not', 2, 6, 0, [[10, 1], [30, 0]]], [[16, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [10, 0]]], [[12, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[1, 1]]], [[5, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [21, 0]]], [[25, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [41, 1]]], [[15, 1], [20, 0], [46, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 5, 5, 0, [[10, 1], [13, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [22, 0]]], [[12, 1], [26, 0]]), ('inverter uses output polarity for delay', ['not', 2, 7, 0, [[10, 1], [30, 0]]], [[17, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [11, 0]]], [[13, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[2, 1]]], [[6, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [22, 0]]], [[26, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [42, 1]]], [[15, 1], [20, 0], [47, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 6, 6, 0, [[10, 1], [14, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [23, 0]]], [[12, 1], [27, 0]]), ('inverter uses output polarity for delay', ['not', 2, 8, 0, [[10, 1], [30, 0]]], [[18, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [12, 0]]], [[14, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[3, 1]]], [[7, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [23, 0]]], [[27, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [43, 1]]], [[15, 1], [20, 0], [48, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 7, 7, 0, [[10, 1], [15, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [24, 0]]], [[12, 1], [28, 0]]), ('inverter uses output polarity for delay', ['not', 2, 9, 0, [[10, 1], [30, 0]]], [[19, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [13, 0]]], [[15, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[4, 1]]], [[8, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [24, 0]]], [[28, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [44, 1]]], [[15, 1], [20, 0], [49, 1]])], [('pulse shorter than inertial delay is filtered', ['buf', 8, 8, 0, [[10, 1], [16, 0]]], []), ('wide pulse passes with rise and fall delays', ['buf', 2, 4, 0, [[10, 1], [25, 0]]], [[12, 1], [29, 0]]), ('inverter uses output polarity for delay', ['not', 2, 10, 0, [[10, 1], [30, 0]]], [[20, 0], [32, 1]]), ('redundant input event produces no output edge', ['buf', 1, 2, 1, [[5, 1], [14, 0]]], [[16, 0]]), ('final pending event is committed', ['buf', 4, 4, 0, [[5, 1]]], [[9, 1]]), ('inverter glitch cancelled', ['not', 4, 4, 1, [[10, 0], [12, 1], [25, 0]]], [[29, 1]]), ('output matures exactly at next input change', ['buf', 5, 5, 0, [[10, 1], [15, 0], [45, 1]]], [[15, 1], [20, 0], [50, 1]])]]
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
pulse shorter than inertial delay is filtered[][]Passed
wide pulse passes with rise and fall delays[[12, 1], [25, 0]][[12, 1], [25, 0]]Passed
inverter uses output polarity for delay[[16, 0], [32, 1]][[16, 0], [32, 1]]Passed
redundant input event produces no output edge[[12, 0]][[12, 0]]Passed
final pending event is committed[[5, 1]][[5, 1]]Passed
inverter glitch cancelled[[25, 1]][[25, 1]]Passed
output matures exactly at next input change[[15, 1], [20, 0], [46, 1]][[15, 1], [20, 0], [46, 1]]Passed

SHA-256 / 1ebee7a5486716e88dd2c30db51d1a01b4d600a97674fb1d7e90483329d0d274

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 2026-09-29T14:51:12.290848+00:00.

Case digest / 764f8d65708ba7eebfeada9340595ea155a709feaf56110ccc2230cd8ff82868