FA-88956 / Digital logic simulation / Open access

Clock assumed low before the first transition · case 01

A clock that starts high reports a phantom rising edge at its first redundant transition.

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

ROOT CAUSE

The edge detector ignores the declared initial clock level and assumes 0.

THE FAILURE

The edge detector ignores the declared initial clock level and assumes 0.

Unsuccessful approach: Seeding from the first transition value hides a genuine first rising edge.

Case contract

Input [c0, clock, data, setup, hold]: c0 is the initial clock level, clock is time-sorted [t, v] transitions (possibly redundant), data is a list of data transition times. Rising edges are 0->1 changes only. For every data time t and every rising edge e: e-setup < t < e is a 'setup' violation, e <= t < e+hold is a 'hold' violation. Return all [e, t, kind] sorted by edge, then time.

Why this case matters

Timing checks in gate-level simulation decide which transitions corrupt a register; window boundaries and edge extraction are the classic bug sites.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(*args):
    c0, clock, data, s, h = args
    edges = []
    prev = 0
    for t, v in clock:
        if prev == 0 and v == 1:
            edges.append(t)
        prev = v
    out = []
    for t in data:
        for e in edges:
            if e - s < t < e:
                out.append([e, t, 'setup'])
            elif e <= t < e + h:
                out.append([e, t, 'hold'])
    return sorted(out)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 18, 27], 3, 2], [[10, 8, 'setup'], [20, 18, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 29], 3, 2], [[20, 20, 'hold'], [30, 29, 'setup']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 25], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [21, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [13, 1]], [3, 5, 11], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 6], 2, 2], [[4, 3, 'setup']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])], [('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 19, 27], 3, 2], [[10, 8, 'setup'], [20, 19, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 30], 3, 2], [[20, 20, 'hold'], [30, 30, 'hold']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 26], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [22, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [14, 1]], [3, 5, 12], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 5], 2, 2], [[4, 3, 'setup'], [4, 5, 'hold']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])], [('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 17, 27], 3, 2], [[10, 8, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 29], 3, 2], [[20, 20, 'hold'], [30, 29, 'setup']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 25], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [23, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [15, 1]], [3, 5, 13], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 6], 2, 2], [[4, 3, 'setup']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])], [('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 18, 27], 3, 2], [[10, 8, 'setup'], [20, 18, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 30], 3, 2], [[20, 20, 'hold'], [30, 30, 'hold']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 26], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [24, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [16, 1]], [3, 5, 14], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 5], 2, 2], [[4, 3, 'setup'], [4, 5, 'hold']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])], [('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 19, 27], 3, 2], [[10, 8, 'setup'], [20, 19, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 29], 3, 2], [[20, 20, 'hold'], [30, 29, 'setup']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 25], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [25, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [17, 1]], [3, 5, 15], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 6], 2, 2], [[4, 3, 'setup']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])]]
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
setup window boundaries	`[[10, 8, 'setup'], [20, 18, 'setup']]`	`[[10, 8, 'setup'], [20, 18, 'setup']]`	Passed
transition exactly at the clock edge	`[[20, 20, 'hold'], [30, 29, 'setup']]`	`[[20, 20, 'hold'], [30, 29, 'setup']]`	Passed
falling clock edges are not checked	`[]`	`[]`	Passed
redundant high transition is not an edge	`[]`	`[]`	Passed
clock already high at start	`[[4, 3, 'setup'], [4, 5, 'hold']]`	`[]`	Failed
clock low at start rises first	`[[4, 3, 'setup']]`	`[[4, 3, 'setup']]`	Passed
overlapping windows reported by edge	`[[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']]`	`[[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']]`	Passed

SHA-256 / be46ba0a9f3a8b03847952dcfaae88a5054f52d5a71d4d0293adf82d6eaa536a

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(*args):
    c0, clock, data, s, h = args
    edges = []
    prev = clock[0][1] if clock else c0
    for t, v in clock:
        if prev == 0 and v == 1:
            edges.append(t)
        prev = v
    out = []
    for t in data:
        for e in edges:
            if e - s < t < e:
                out.append([e, t, 'setup'])
            elif e <= t < e + h:
                out.append([e, t, 'hold'])
    return sorted(out)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 18, 27], 3, 2], [[10, 8, 'setup'], [20, 18, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 29], 3, 2], [[20, 20, 'hold'], [30, 29, 'setup']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 25], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [21, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [13, 1]], [3, 5, 11], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 6], 2, 2], [[4, 3, 'setup']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])], [('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 19, 27], 3, 2], [[10, 8, 'setup'], [20, 19, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 30], 3, 2], [[20, 20, 'hold'], [30, 30, 'hold']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 26], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [22, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [14, 1]], [3, 5, 12], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 5], 2, 2], [[4, 3, 'setup'], [4, 5, 'hold']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])], [('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 17, 27], 3, 2], [[10, 8, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 29], 3, 2], [[20, 20, 'hold'], [30, 29, 'setup']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 25], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [23, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [15, 1]], [3, 5, 13], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 6], 2, 2], [[4, 3, 'setup']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])], [('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 18, 27], 3, 2], [[10, 8, 'setup'], [20, 18, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 30], 3, 2], [[20, 20, 'hold'], [30, 30, 'hold']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 26], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [24, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [16, 1]], [3, 5, 14], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 5], 2, 2], [[4, 3, 'setup'], [4, 5, 'hold']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])], [('setup window boundaries', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [7, 8, 19, 27], 3, 2], [[10, 8, 'setup'], [20, 19, 'setup']]), ('transition exactly at the clock edge', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [20, 22, 29], 3, 2], [[20, 20, 'hold'], [30, 29, 'setup']]), ('falling clock edges are not checked', [0, [[10, 1], [15, 0], [20, 1], [25, 0], [30, 1]], [16, 25], 3, 2], []), ('redundant high transition is not an edge', [0, [[5, 1], [10, 1], [12, 0], [25, 1]], [9, 11], 3, 2], []), ('clock already high at start', [1, [[4, 1], [8, 0], [17, 1]], [3, 5, 15], 2, 2], []), ('clock low at start rises first', [0, [[4, 1], [8, 0], [12, 1]], [3, 6], 2, 2], [[4, 3, 'setup']]), ('overlapping windows reported by edge', [0, [[10, 1], [11, 0], [12, 1]], [11, 12], 3, 3], [[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']])]]
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
setup window boundaries	`[[20, 18, 'setup']]`	`[[10, 8, 'setup'], [20, 18, 'setup']]`	Failed
transition exactly at the clock edge	`[[20, 20, 'hold'], [30, 29, 'setup']]`	`[[20, 20, 'hold'], [30, 29, 'setup']]`	Passed
falling clock edges are not checked	`[]`	`[]`	Passed
redundant high transition is not an edge	`[]`	`[]`	Passed
clock already high at start	`[]`	`[]`	Passed
clock low at start rises first	`[]`	`[[4, 3, 'setup']]`	Failed
overlapping windows reported by edge	`[[12, 11, 'setup'], [12, 12, 'hold']]`	`[[10, 11, 'hold'], [10, 12, 'hold'], [12, 11, 'setup'], [12, 12, 'hold']]`	Failed

SHA-256 / f97e527ac3f54c7d71d99d9a29cec93ce574d6a412a4be7e66bc36df6858cc71

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 2026-09-29T14:51:12.984258+00:00.

Case digest / 3c0b8e9fc3507c9465faa4af3cd99df9c6e2cc21f40f560ea3a75bdd73269de4