Edge and Embedded Systems Engineering

# Confirm the running kernel was built with PREEMPT_RT
uname -v | grep -o 'PREEMPT_RT' || echo "not a PREEMPT_RT kernel"

# One hour with the device workload running: locked memory, one measuring
# thread per core at priority 80, 200 µs interval, histogram up to 400 µs
sudo cyclictest --mlockall --smp --priority=80 --interval=200 \
  --distance=0 --duration=1h --histogram=400 --quiet > run-r1.hist

-- Synthetic illustration: worst-case scheduling latency per test run, from
-- cyclictest histograms loaded into the device's local SQLite sink.
-- TEMP stand-ins: they vanish with the session and never touch the file.
CREATE TEMP TABLE IF NOT EXISTS latency_run (
  run_id TEXT PRIMARY KEY, board TEXT NOT NULL, kernel TEXT NOT NULL,
  load_profile TEXT NOT NULL, started_utc TEXT NOT NULL
);
CREATE TEMP TABLE IF NOT EXISTS latency_bucket (
  run_id TEXT NOT NULL REFERENCES latency_run(run_id),
  latency_us INTEGER NOT NULL, samples INTEGER NOT NULL
);

SELECT r.run_id,
       r.kernel,
       r.load_profile,
       MAX(b.latency_us)  AS worst_case_us,
       SUM(b.samples)     AS samples,
       SUM(CASE WHEN b.latency_us > 100 THEN b.samples ELSE 0 END) AS over_budget
FROM latency_run r
JOIN latency_bucket b ON b.run_id = r.run_id
WHERE b.samples > 0
GROUP BY r.run_id, r.kernel, r.load_profile
ORDER BY worst_case_us DESC;

-- Synthetic illustration: sensor readings whose device timestamp drifts from
-- the monotonic receive clock by more than the agreed tolerance (5 ms).
CREATE TEMP TABLE IF NOT EXISTS sensor_reading (
  sensor_id TEXT NOT NULL, seq INTEGER NOT NULL,
  device_ts_us INTEGER NOT NULL, received_mono_us INTEGER NOT NULL,
  PRIMARY KEY (sensor_id, seq)
);

SELECT sensor_id, seq, drift_us
FROM (
  SELECT sensor_id,
         seq,
         (received_mono_us - device_ts_us)
           - FIRST_VALUE(received_mono_us - device_ts_us)
               OVER (PARTITION BY sensor_id ORDER BY seq) AS drift_us
  FROM sensor_reading
)
WHERE ABS(drift_us) > 5000
ORDER BY sensor_id, seq;