FA-88866 / Digital logic simulation / Open access
Gate delay behaves as transport delay · case 01
A pulse narrower than the gate delay appears on the output instead of being swallowed.
ROOT CAUSE
Pending output events are never cancelled when a new input change arrives.
VERIFIED REPAIR
Cancel all pending output events whenever the input changes, then schedule the new value.
Unsuccessful approach: Keeping the most recent pending event still lets the leading edge of a narrow pulse through.
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 + [[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
pass
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 fixture | Actual | Expected | Outcome |
|---|---|---|---|
| pulse shorter than inertial delay is filtered | [[14, 1], [16, 0]] | [] | Failed |
| 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 | [[14, 1], [16, 0], [25, 1]] | [[25, 1]] | Failed |
| output matures exactly at next input change | [[15, 1], [20, 0], [46, 1]] | [[15, 1], [20, 0], [46, 1]] | Passed |
SHA-256 / 37839b9161157203d69f38753ce669b7c0c17c01008a4e7b3f5ff7ab6084b968
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 + [[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 = q[-1:]
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 fixture | Actual | Expected | Outcome |
|---|---|---|---|
| pulse shorter than inertial delay is filtered | [[14, 1], [16, 0]] | [] | Failed |
| 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 | [[14, 1], [16, 0], [25, 1]] | [[25, 1]] | Failed |
| output matures exactly at next input change | [[15, 1], [20, 0], [46, 1]] | [[15, 1], [20, 0], [46, 1]] | Passed |
SHA-256 / 149e79532757f4e918ff78e12c5bb6af44463541200470d25e5bba6dccde04f4
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 fixture | Actual | Expected | Outcome |
|---|---|---|---|
| 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 2026-09-29T14:51:12.076385+00:00.
Case digest / fef10681457517e7cad9b594bb25bde6d0107e5bd55b793045b55175563bf719