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Real-Time Headless Scope

File: examples/advanced/03_realtime_scope/03_realtime_scope.py

What this example shows​

A read-only bus monitor that attaches to an existing shared memory bus and displays live signal values in the terminal — no GUI required. It demonstrates the observer pattern: any number of monitors can attach to the bus without affecting the closed-loop simulation.

Architecture​

The dashed line indicates the monitor never writes to the bus — it is completely transparent to the simulation.

Use cases​

  • Debugging over SSH — no display server needed
  • Logging — redirect stdout to a file: script.py >> log.txt
  • Sanity checking before launching a full matplotlib oscilloscope
  • CI pipelines — verify signals are non-zero without a GUI

Code​

from synapsys.transport import SharedMemoryTransport
import time, sys

monitor = SharedMemoryTransport("sil_bus", {"y": 1, "u": 1}, create=False)
start_time = time.time()

while True:
    y = monitor.read("y")[0]
    u = monitor.read("u")[0]
    elapsed = time.time() - start_time

    sys.stdout.write(
        f"\r[t={elapsed:6.2f}s] y(t): {y:8.4f} | u(t): {u:8.4f}"
    )
    sys.stdout.flush()
    time.sleep(0.05)   # 20 Hz display rate

How the in-place update works​

\r (carriage return) moves the cursor to the beginning of the current line without advancing to the next line. Combined with sys.stdout.flush(), this creates a continuously updating single line — the classic terminal oscilloscope effect.

time.sleep(0.05) sets a 20 Hz display rate. The actual simulation runs at 100 Hz — the monitor samples it at a lower rate, which is sufficient for visual inspection.

How to run​

Requires the plant and controller already running:

# Terminal 1
uv run python examples/advanced/02_sil_ai_controller/02a_sil_plant.py

# Terminal 2
uv run python examples/advanced/02_sil_ai_controller/02b_sil_ai_controller.py

# Terminal 3 — headless monitor
uv run python examples/advanced/03_realtime_scope/03_realtime_scope.py

Press Ctrl+C to stop the monitor. The plant and controller keep running.