Phase 5: shared worker base, self-rescheduling polls, driver robustness

gui/qt_workers.py — one QueueWorker base replaces the per-device command
queue + dispatch + signal boilerplate. The loop blocks on the queue
instead of waking 10-20x/second forever (test_idle_worker_does_not_spin
asserts an idle worker burns ~no CPU). PollingQueueWorker adds
self-rescheduling polling: the next poll is queued only after the
previous finishes, so a device slower than the interval can't accumulate
a backlog (test_polling_never_overlaps_or_backs_up).

Helios responsiveness — the concrete bug that motivated the above: a free
running 1 s QTimer queued a status poll that took ~2 s, so the queue grew
for as long as the panel stayed connected.
- helios_laser._query reads until the CR terminator instead of sleeping a
  fixed 0.05 + 0.2 s per query
- one _query_int() helper replaces five copies of parse-with-logging
- polling is now driven by the worker; HeliosWindow's QTimer is gone
- dropped __del__, which disabled the laser and wrote to the serial port
  from the garbage collector at an unpredictable time

helios_test_app.py — the worker was moveToThread'd but every call site
invoked its methods directly, so all serial I/O (including the sleeps)
ran on the GUI thread; Query All froze the UI for ~2 s. Calls now go
through a queued signal to a pyqtSlot. Also: connect/disconnect cycles
leaked a QThread + worker + 9 connections each time; 16 copies of the
not-connected guard collapse to _require_connection(); the Query Power
button called a method that has never existed (AttributeError popup) and
is now disabled and documented in KNOWN_ISSUES.

DCBiasImageWidget preallocates its image and uses set_data/set_clim, so
the live preview stops rebuilding the array and the whole artist tree per
row (O(rows^2) over a scan).

bbd20x: connect() now raises when no bays respond instead of reporting
success on the wrong port; disconnect() joins with a timeout so a wedged
reader can't hang shutdown; one _channel_for() helper replaces four
copy-pasted axis mappings; hardcoded travel limits become TRAVEL_MM; the
joke error strings are gone.

gui/widgets.py adds the shared ConnectionBar / PortSelector / bounded
LogConsole / StatusGrid for the test benches to adopt. 65 tests passing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

KNOWN_ISSUES.md

@@ -17,6 +17,20 @@ If they appear, the setters need a stop-live/apply/restart sequence
 (re-create the helper around the two call sites in
 [uc480_camera.py](hardware/uc480_camera.py)).
 
+## Helios: no output-power query
+
+`docs/hardware/HELIOS_DRIVER_README.md` documents `driver.get_power_mw()`,
+but `HeliosLaser` has no such method and no output-power mnemonic appears
+anywhere in this repo's protocol notes. `helios_test_app.py` called it
+anyway and raised `AttributeError` into a popup; the button is now disabled
+and the handler reports the gap instead.
+
+**Bench check:** find the power-read command in the Helios manual (the
+other reads are three-letter mnemonics like `LDO`, `LDS`, `LTA`). If one
+exists, add `get_power_mw()` to `hardware/helios_laser.py` using
+`_query_int`, then re-enable the button. If it doesn't, delete the Power
+Monitoring group from the test app and fix the README.
+
 ## Genesis laser: forked protocol implementations disagree
 
 `hardware/genesis_core.py` and the reference implementation

gui/qt_workers.py

@@ -0,0 +1,118 @@
+"""Shared Qt worker base for hardware that must be driven off the GUI thread.
+
+Every device worker in this project was the same shape: a command queue, a
+`while running: get(timeout=…)` loop, an if/elif dispatch, and a standard
+connected/disconnected/failed signal trio.  The timeout-poll versions woke
+10–20 times a second forever, even with nothing to do; this base blocks on
+the queue instead and wakes only when there is work.
+"""
+
+from __future__ import annotations
+
+import queue
+
+from PyQt6.QtCore import QObject, pyqtSignal, pyqtSlot
+
+_STOP = object()
+
+
+class QueueWorker(QObject):
+    """Base for a device worker living on its own QThread.
+
+    Subclasses register handlers in ``self._handlers`` (command name →
+    callable) and call ``self._enqueue(name, **kwargs)`` from the GUI thread.
+    Override ``_on_stop`` to release hardware when the loop exits.
+    """
+
+    connected = pyqtSignal()
+    disconnected = pyqtSignal()
+    connection_failed = pyqtSignal(str)
+    error_occurred = pyqtSignal(str)
+
+    def __init__(self):
+        super().__init__()
+        self._cmd_q: queue.Queue = queue.Queue()
+        self._handlers: dict[str, callable] = {}
+        self._running = False
+        self.is_connected = False
+
+    # ── Command submission (GUI thread) ───────────────────────────────────────
+
+    def _enqueue(self, cmd_type: str, **kwargs):
+        self._cmd_q.put((cmd_type, kwargs))
+
+    def stop_worker(self):
+        self._cmd_q.put(_STOP)
+
+    # ── Worker loop ───────────────────────────────────────────────────────────
+
+    @pyqtSlot()
+    def run(self):
+        self._running = True
+        while self._running:
+            item = self._cmd_q.get()      # blocks — no idle wake-ups
+            if item is _STOP:
+                break
+            cmd_type, kwargs = item
+            handler = self._handlers.get(cmd_type)
+            if handler is None:
+                self.error_occurred.emit(f"Unknown command: {cmd_type}")
+                continue
+            try:
+                handler(**kwargs)
+            except Exception as exc:
+                self.error_occurred.emit(str(exc))
+        self._running = False
+        self._on_stop()
+
+    def _on_stop(self):
+        """Release hardware when the loop exits.  Override as needed."""
+
+
+class PollingQueueWorker(QueueWorker):
+    """QueueWorker that also polls the device on an interval.
+
+    The poll is self-rescheduling: the next one is queued only after the
+    previous finishes, so a device slower than the interval can never
+    accumulate a backlog of stale poll commands (which is exactly what the
+    old free-running QTimer did to the Helios laser).
+    """
+
+    POLL_CMD = "_poll"
+
+    def __init__(self, poll_interval_s: float = 1.0):
+        super().__init__()
+        self._poll_interval_s = poll_interval_s
+        self._polling = False
+        self._handlers[self.POLL_CMD] = self._poll_and_reschedule
+
+    def start_polling(self):
+        if not self._polling:
+            self._polling = True
+            self._enqueue(self.POLL_CMD)
+
+    def stop_polling(self):
+        self._polling = False
+
+    def _poll_and_reschedule(self):
+        if not self._polling or not self.is_connected:
+            self._polling = False
+            return
+        try:
+            self._poll_once()
+        finally:
+            if self._polling and self.is_connected:
+                self._schedule_next_poll()
+
+    def _schedule_next_poll(self):
+        # A timer thread rather than a sleep here, so the worker stays
+        # responsive to commands during the interval.
+        import threading
+        t = threading.Timer(self._poll_interval_s,
+                            lambda: self._enqueue(self.POLL_CMD))
+        t.daemon = True
+        t.start()
+        self._poll_timer = t
+
+    def _poll_once(self):
+        """Read device state and emit updates.  Implemented by subclasses."""

gui/widgets.py

@@ -0,0 +1,187 @@
+"""Widgets shared by the main app and the per-device test benches.
+
+Each of these was hand-rolled several times across the apps, with slightly
+different behaviour every time (only one log console bounded its buffer,
+only one port picker sorted by device type).
+"""
+
+from __future__ import annotations
+
+from PyQt6.QtCore import Qt, pyqtSignal
+from PyQt6.QtGui import QFont
+from PyQt6.QtWidgets import (
+    QComboBox, QGroupBox, QHBoxLayout, QLabel, QPlainTextEdit, QPushButton,
+    QVBoxLayout, QWidget,
+)
+
+from hardware.serial_util import scored_ports
+
+
+def set_toggle(btn, checked: bool, text: str, enabled: bool = True):
+    """Update a checkable button without re-triggering its toggled signal."""
+    btn.blockSignals(True)
+    btn.setChecked(checked)
+    btn.setText(text)
+    btn.setEnabled(enabled)
+    btn.blockSignals(False)
+
+
+class PortSelector(QWidget):
+    """Serial port combo + refresh button, likeliest device first."""
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        row = QHBoxLayout(self)
+        row.setContentsMargins(0, 0, 0, 0)
+        self.combo = QComboBox()
+        self.combo.setMinimumWidth(220)
+        refresh = QPushButton("⟳")
+        refresh.setFixedWidth(30)
+        refresh.setToolTip("Rescan serial ports")
+        refresh.clicked.connect(self.refresh)
+        row.addWidget(self.combo, stretch=1)
+        row.addWidget(refresh)
+        self.refresh()
+
+    def refresh(self):
+        """Repopulate the list, preserving the current selection if present."""
+        current = self.current_port()
+        self.combo.clear()
+        for device, label in scored_ports():
+            self.combo.addItem(label, device)
+        if self.combo.count() == 0:
+            self.combo.addItem("(no serial ports found)", None)
+        elif current:
+            idx = self.combo.findData(current)
+            if idx >= 0:
+                self.combo.setCurrentIndex(idx)
+
+    def current_port(self) -> str | None:
+        return self.combo.currentData()
+
+    def set_port(self, device: str):
+        idx = self.combo.findData(device)
+        if idx >= 0:
+            self.combo.setCurrentIndex(idx)
+
+
+class ConnectionBar(QGroupBox):
+    """Port picker + connect toggle + status label.
+
+    Emits connect_requested(port) / disconnect_requested(); the owner drives
+    the state back through on_connected/on_disconnected/on_failed so the
+    button can never disagree with the hardware.
+    """
+
+    connect_requested = pyqtSignal(str)
+    disconnect_requested = pyqtSignal()
+
+    def __init__(self, title: str = "Connection", parent=None):
+        super().__init__(title, parent)
+        layout = QVBoxLayout(self)
+        self.port_selector = PortSelector()
+        layout.addWidget(self.port_selector)
+
+        row = QHBoxLayout()
+        self.toggle = QPushButton("Connect")
+        self.toggle.setCheckable(True)
+        self.toggle.toggled.connect(self._on_toggled)
+        self.status = QLabel("Disconnected")
+        self.status.setStyleSheet("font-weight: bold;")
+        row.addWidget(self.toggle)
+        row.addWidget(self.status, stretch=1)
+        layout.addLayout(row)
+
+    def _on_toggled(self, checked: bool):
+        if checked:
+            port = self.port_selector.current_port()
+            if not port:
+                set_toggle(self.toggle, False, "Connect")
+                self.status.setText("No port selected")
+                return
+            self.toggle.setText("Connecting…")
+            self.toggle.setEnabled(False)
+            self.connect_requested.emit(port)
+        else:
+            self.disconnect_requested.emit()
+
+    def on_connected(self, detail: str = "Connected"):
+        set_toggle(self.toggle, True, "Disconnect")
+        self.status.setText(detail)
+        self.status.setStyleSheet("font-weight: bold; color: green;")
+
+    def on_disconnected(self, detail: str = "Disconnected"):
+        set_toggle(self.toggle, False, "Connect")
+        self.status.setText(detail)
+        self.status.setStyleSheet("font-weight: bold;")
+
+    def on_failed(self, message: str):
+        set_toggle(self.toggle, False, "Connect")
+        self.status.setText(f"Failed: {message}")
+        self.status.setStyleSheet("font-weight: bold; color: red;")
+
+
+class LogConsole(QWidget):
+    """Bounded, monospace, auto-scrolling log view with a Clear button.
+
+    The block cap is the point: unbounded QTextEdit logs grew for the whole
+    session in every app that hand-rolled one.
+    """
+
+    KINDS = {"tx": "→", "rx": "←", "info": "●", "err": "!"}
+
+    def __init__(self, max_blocks: int = 2000, parent=None):
+        super().__init__(parent)
+        layout = QVBoxLayout(self)
+        layout.setContentsMargins(0, 0, 0, 0)
+
+        self.view = QPlainTextEdit()
+        self.view.setReadOnly(True)
+        self.view.setMaximumBlockCount(max_blocks)
+        font = QFont("Menlo")
+        font.setStyleHint(QFont.StyleHint.Monospace)
+        font.setPointSize(11)
+        self.view.setFont(font)
+        layout.addWidget(self.view)
+
+        row = QHBoxLayout()
+        row.addStretch(1)
+        clear = QPushButton("Clear")
+        clear.clicked.connect(self.view.clear)
+        row.addWidget(clear)
+        layout.addLayout(row)
+
+    def log(self, message: str, kind: str = "info"):
+        self.view.appendPlainText(f"{self.KINDS.get(kind, '●')} {message}")
+        self.view.verticalScrollBar().setValue(
+            self.view.verticalScrollBar().maximum())
+
+
+class StatusGrid(QWidget):
+    """Label/value rows with consistent ok/warn/error colouring."""
+
+    _COLORS = {"ok": "green", "warn": "#b8860b", "error": "red", "": ""}
+
+    def __init__(self, fields: list[str], parent=None):
+        super().__init__(parent)
+        layout = QVBoxLayout(self)
+        layout.setContentsMargins(0, 0, 0, 0)
+        self._values: dict[str, QLabel] = {}
+        for name in fields:
+            row = QHBoxLayout()
+            label = QLabel(f"{name}:")
+            value = QLabel("—")
+            value.setAlignment(Qt.AlignmentFlag.AlignRight
+                               | Qt.AlignmentFlag.AlignVCenter)
+            row.addWidget(label)
+            row.addWidget(value, stretch=1)
+            layout.addLayout(row)
+            self._values[name] = value
+
+    def set(self, name: str, text: str, state: str = ""):
+        label = self._values.get(name)
+        if label is None:
+            return
+        label.setText(text)
+        color = self._COLORS.get(state, "")
+        label.setStyleSheet(f"color: {color};" if color else "")

hardware/helios_laser.py

@@ -115,37 +115,36 @@ class HeliosLaser:
             return False
 
     def _query(self, command: str) -> Optional[str]:
-        """
+        """Send a query and return the value from its response.
-        Send a query and read response.
 
-        Args:
+        Reads until the CR terminator rather than sleeping a fixed interval:
-            command: ASCII query command (without CR or ?)
+        the device usually answers in a few ms, so the old unconditional
-
+        0.05 + 0.2 s cost ~250 ms per query and made an 8-query status poll
-        Returns:
+        take ~2 s — longer than the 1 s interval that scheduled it.
-            Response value string or None if error
         """
         try:
-            # Clear any pending data in the buffer
+            # Clear any stale bytes so a previous timed-out reply can't be
+            # mistaken for this command's response.
             self.serial.reset_input_buffer()
-            time.sleep(0.05)
 
             if not self._send_command(command):
                 return None
 
-            time.sleep(0.2)  # Give device time to respond
-
             response = self.serial.read_until(b'\r').decode('ascii', errors='replace').strip()
+            if not response:
+                logger.warning(f"Query '{command}' timed out after {self.timeout}s")
+                return None
             logger.debug(f"Query '{command}' response: {response}")
 
-            # Helios format: "COMMAND = VALUE UNIT"
+            # Helios format: "COMMAND = VALUE UNIT" — take just the value
-            # Extract just the value part
             if '=' in response:
                 parts = response.split('=')
                 if len(parts) >= 2:
                     value_part = parts[1].strip()
-                    # Remove unit suffix if present (e.g., "ns", "mA", "mW")
+                    # Strip the unit suffix if present (e.g. "ns", "mA", "mW")
-                    value = value_part.split()[0]
+                    fields = value_part.split()
-                    return value
+                    if fields:
+                        return fields[0]
 
             return response
 
@@ -153,6 +152,17 @@ class HeliosLaser:
             logger.error(f"Failed to read response for '{command}': {e}")
             return None
 
+    def _query_int(self, command: str) -> Optional[int]:
+        """Query a value that should parse as an int; None if absent/unparseable."""
+        raw = self._query(command)
+        if raw is None:
+            return None
+        try:
+            return int(raw)
+        except ValueError:
+            logger.error(f"Query '{command}' returned non-integer {raw!r}")
+            return None
+
     def set_frequency_hz(self, frequency: int) -> bool:
         """
         Set laser pulse frequency in Hz.
@@ -228,60 +238,24 @@ class HeliosLaser:
         return success
 
     def is_laser_enabled(self) -> bool:
-        """
+        """True if laser emission is currently enabled."""
-        Check if laser is currently enabled.
+        return self._query_int("LDO") == 1
-
-        Returns:
-            True if laser is enabled
-        """
-        response = self._query("LDO")
-        if response:
-            try:
-                return int(response) == 1
-            except ValueError:
-                logger.error(f"Invalid response for LDO: {response}")
-        return False
 
     def get_frequency_hz(self) -> Optional[int]:
-        """
+        """Current laser frequency in Hz, or None on error."""
-        Get current laser frequency in Hz.
+        period_ns = self._query_int("LDF")
-
+        if not period_ns:
-        Returns:
-            Frequency in Hz or None if error
-        """
-        response = self._query("LDF")
-        if response:
-            try:
-                period_ns = int(response)
-                return int(1e9 / period_ns)
-            except (ValueError, ZeroDivisionError):
-                logger.error(f"Invalid response for LDF: {response}")
             return None
+        return int(1e9 / period_ns)
 
     def get_current_ma(self) -> Optional[int]:
-        """
+        """Current pump diode current in mA, or None on error."""
-        Get current pump diode current in mA.
+        return self._query_int("LDS")
-
-        Returns:
-            Current in mA or None if error
-        """
-        response = self._query("LDS")
-        if response:
-            try:
-                return int(response)
-            except ValueError:
-                logger.error(f"Invalid response for LDS: {response}")
-        return None
 
     def _query_millicelsius(self, command: str) -> Optional[float]:
-        """Query a temperature register (returns milli-°C) and convert to °C."""
+        """Query a temperature register (milli-°C) and convert to °C."""
-        response = self._query(command)
+        value = self._query_int(command)
-        if response:
+        return None if value is None else value / 1000.0
-            try:
-                return int(response) / 1000.0
-            except ValueError:
-                logger.error(f"Invalid response for {command}: {response}")
-        return None
 
     def get_diode_temp_c(self) -> Optional[float]:
         """Diode temperature in °C (LTA, 5000–50000 milli-°C)."""
@@ -296,46 +270,22 @@ class HeliosLaser:
         return self._query_millicelsius("EOA")
 
     def get_controller_serial(self) -> Optional[str]:
-        """
+        """Controller serial number, or None on error."""
-        Get controller serial number.
-
-        Returns:
-            Serial number string or None if error
-        """
         return self._query("CSR")
 
     def get_head_serial(self) -> Optional[str]:
-        """
+        """Laser head serial number, or None on error."""
-        Get laser head serial number.
-
-        Returns:
-            Serial number string or None if error
-        """
         return self._query("HSR")
 
     def get_status_registers(self) -> tuple:
+        """Query the LER, LCE and CCE status registers.
+
+        Each is a bitmask (sum of flags); non-zero means active faults,
+        cleared with reset_faults().  Returns (ler, lce, cce), any of which
+        is None if that register could not be read.
         """
-        Query LER, LCE, and CCE status registers.
+        return (self._query_int("LER"), self._query_int("LCE"),
-
+                self._query_int("CCE"))
-        Each register is a bitmask (sum of flags). Non-zero values indicate
-        active faults. Reset with reset_faults().
-
-        Returns:
-            Tuple of (ler, lce, cce) as ints, or None for each on error.
-        """
-        def _read_reg(cmd):
-            resp = self._query(cmd)
-            if resp is not None:
-                try:
-                    return int(resp)
-                except ValueError:
-                    logger.error(f"Invalid response for {cmd}: {resp}")
-            return None
-
-        ler = _read_reg("LER")
-        lce = _read_reg("LCE")
-        cce = _read_reg("CCE")
-        return (ler, lce, cce)
 
     def reset_faults(self) -> bool:
         """
@@ -357,38 +307,19 @@ class HeliosLaser:
         return ok
 
     def get_remote_enable(self) -> Optional[bool]:
-        """
+        """Remote enable state (LRE — utility connector pin 8); None on error."""
-        Query the remote enable state (LRE - activates utility connector pin 8).
+        value = self._query_int("LRE")
-
+        return None if value is None else value == 1
-        Returns:
-            True if remote enable is active, False if not, None on error
-        """
-        response = self._query("LRE")
-        if response is not None:
-            try:
-                return int(response) == 1
-            except ValueError:
-                logger.error(f"Invalid response for LRE: {response}")
-        return None
 
     def send_raw_command(self, command: str) -> Optional[str]:
-        """
+        """Send a raw command and return the unparsed response (diagnostics)."""
-        Send a raw command string and return the raw response.
-
-        Useful for diagnostics. Sends *command* + CR, waits briefly,
-        then reads whatever the device returns (up to the first CR or timeout).
-
-        Returns:
-            Raw response string (decoded, stripped) or None on error.
-        """
         if not self.is_connected or not self.serial:
             logger.error("Not connected to laser")
             return None
         try:
             self.serial.reset_input_buffer()
-            time.sleep(0.05)
+            if not self._send_command(command):
-            self.serial.write((command + '\r').encode('ascii'))
+                return None
-            time.sleep(0.3)
             raw = self.serial.read_until(b'\r')
             if not raw:
                 raw = self.serial.read(self.serial.in_waiting)
@@ -410,6 +341,7 @@ class HeliosLaser:
         command = f"LRE {1 if enable else 0}"
         return self._send_command(command)
 
-    def __del__(self):
+    # No __del__: it used to call disconnect(), which disables the laser and
-        """Destructor - ensure cleanup"""
+    # writes to the serial port from the garbage collector at an
-        self.disconnect()
+    # unpredictable time (including interpreter shutdown, when the port may
+    # already be torn down).  Callers close the driver explicitly.

hardware/pybbd202/bbd20x.py

@@ -12,12 +12,18 @@ from .apt_messages import APTProtocol
 from .serial_comms import SerialSnooper
 
 
+# APT bay addresses for the two stage axes
+AXIS_X_ADDR = 0x21
+AXIS_Y_ADDR = 0x22
+
+
 class ThorlabsServoDriver():
     # These are specific to the MLS203-1
     # change for a different application
     counts_per_mm = 20000
     accel_scaling = 13.744
     velocity_scaling = 134217.73
+    TRAVEL_MM = (110.0, 75.0)   # usable travel per channel (X, Y)
 
     def __init__(self):
         self.am_connected = False
@@ -83,10 +89,27 @@ class ThorlabsServoDriver():
                 pass
 
         if not self.bays_present:
-            print("  [WARN] No bays detected!")
+            # Fail loudly: reporting success with no bays made connecting to
+            # the wrong port look like it worked, and every later command
+            # then silently went nowhere.
+            self.disconnect()
+            raise RuntimeError(
+                f"No BBD202 bays responded on {port}. Check the port, the "
+                f"controller power, and that no other process holds the device."
+            )
 
         self.am_connected = True
 
+    @staticmethod
+    def _channel_for(axis):
+        """Map an APT axis address to this driver's 0-based channel index."""
+        if axis == AXIS_X_ADDR:
+            return 0
+        if axis == AXIS_Y_ADDR:
+            return 1
+        raise ValueError(f"Unknown axis address 0x{axis:02x} "
+                         f"(expected 0x{AXIS_X_ADDR:02x} or 0x{AXIS_Y_ADDR:02x})")
+
     # ── Worker threads ───────────────────────────────────────────
 
     def _tx_worker(self):
@@ -223,15 +246,18 @@ class ThorlabsServoDriver():
                     APTProtocol.build_message(0x0002, destination=addr,
                                               source=0x01))
             time.sleep(0.2)  # let TX worker flush them out
-            # Stop all worker loops, then wait for threads to exit
+            # Stop all worker loops, then wait for threads to exit.  Joins
+            # are bounded: disconnect() runs from closeEvent, and a wedged
+            # reader must not hang application shutdown.
             self.am_listening = False
             self.serial_snoop.stop()
-            self._rx_thread.join()
+            for thread in (self._rx_thread, self._tx_thread, self._poll_thread,
-            self._tx_thread.join()
+                           self.serial_snoop):
-            self._poll_thread.join()
+                if thread is not None:
-            self.serial_snoop.join()
+                    thread.join(timeout=2.0)
             # Close port only after all threads are done
             self.serial_snoop.close()
+        self.am_connected = False
 
     # ── State update handlers ────────────────────────────────────
 
@@ -305,13 +331,8 @@ class ThorlabsServoDriver():
             toggle_enabled_state(axis) - enables the axis if disabled. disables
             if enabled. not much more to it.
         '''
-        if axis == 0x21:
+        ch = self._channel_for(axis)
-            ch = 0
+        # Read the cached state and invert it
-        elif axis == 0x22:
-            ch = 1
-        else:
-            raise ValueError("I don't know that axis!")
-        # get the old state and flip it like a sample
         new_state = not self.am_enabled[ch]
         self.send_message(0x0210, chan_ident=1,
                           enable_state=0x01 if new_state else 0x02,
@@ -323,12 +344,7 @@ class ThorlabsServoDriver():
             power up. Default timeout is 60s, but 20-30s is fine as well if
             you're in that much of a hurry.
         '''
-        if axis == 0x21:
+        ch = self._channel_for(axis)
-            ch = 0
-        elif axis == 0x22:
-            ch = 1
-        else:
-            raise ValueError("I don't know that axis!")
 
         self.send_and_wait(0x0443, timeout=timeout, retries=0, chan_ident=1,
                            destination=axis, source=0x01)
@@ -340,11 +356,11 @@ class ThorlabsServoDriver():
                 moves the specified axis a specified distance in mm.
                 Timeout defaults to ten seconds.
         '''
-        # sanity check
+        travel = self.TRAVEL_MM[self._channel_for(axis)]
-        if axis == 0x21 and abs(distance_in_mm) > 110.0:
+        if abs(distance_in_mm) > travel:
-            raise ValueError("You can't move farther than the stage is long.")
+            raise ValueError(
-        elif axis == 0x22 and abs(distance_in_mm) > 75.0:
+                f"Relative move of {distance_in_mm:.3f} mm exceeds the "
-            raise ValueError("You can't move farther than the stage is wide.")
+                f"{travel:g} mm travel of this axis.")
 
         _distance_in_encoder = int(round(distance_in_mm * self.counts_per_mm))
         self.send_and_wait(0x0448, timeout=timeout, chan_ident=1,
@@ -358,10 +374,12 @@ class ThorlabsServoDriver():
                 moves the specified axis to an absolute position in mm.
                 Timeout defaults to ten seconds.
         '''
-        if axis == 0x21 and (position_in_mm < 0.0 or position_in_mm > 110.0):
+        ch = self._channel_for(axis)
-            raise ValueError("Position out of range for X axis (0-110 mm).")
+        travel = self.TRAVEL_MM[ch]
-        elif axis == 0x22 and (position_in_mm < 0.0 or position_in_mm > 75.0):
+        if not 0.0 <= position_in_mm <= travel:
-            raise ValueError("Position out of range for Y axis (0-75 mm).")
+            raise ValueError(
+                f"Position {position_in_mm:.3f} mm is out of range for the "
+                f"{'XY'[ch]} axis (0-{travel:g} mm).")
 
         _position_in_encoder = int(round(position_in_mm * self.counts_per_mm))
         self.send_and_wait(0x0453, timeout=timeout, chan_ident=1,
@@ -377,12 +395,7 @@ class ThorlabsServoDriver():
             for the specified axis. Returns a dict with keys:
                 min_velocity (mm/s), acceleration (mm/s2), max_velocity (mm/s)
         '''
-        if axis == 0x21:
+        ch = self._channel_for(axis)
-            ch = 0
-        elif axis == 0x22:
-            ch = 1
-        else:
-            raise ValueError("I don't know that axis!")
 
         result = self.send_and_wait(0x0414, timeout=timeout, chan_ident=1,
                                     zero_this=0x00, destination=axis,
@@ -405,12 +418,7 @@ class ThorlabsServoDriver():
                 Values are in mm/s and mm/s2 respectively. Any parameter
                 left as None keeps its current value.
         '''
-        if axis == 0x21:
+        ch = self._channel_for(axis)
-            ch = 0
-        elif axis == 0x22:
-            ch = 1
-        else:
-            raise ValueError("I don't know that axis!")
 
         # Only query current params if we need to fill in a missing value
         if max_velocity is None or acceleration is None:

helios_test_app.py

@@ -12,7 +12,7 @@ from PyQt6.QtWidgets import (
     QGroupBox, QLabel, QLineEdit, QPushButton, QComboBox, QSpinBox,
     QMessageBox, QTabWidget, QTextEdit
 )
-from PyQt6.QtCore import QThread, pyqtSignal, QObject
+from PyQt6.QtCore import QThread, pyqtSignal, pyqtSlot, QObject
 from PyQt6.QtGui import QFont
 
 from hardware.helios_laser import HeliosLaser, PulseMode
@@ -140,6 +140,20 @@ class LaserWorker(QObject):
         super().__init__()
         self.laser = laser
 
+    @pyqtSlot(str, object)
+    def invoke(self, method_name: str, args: tuple):
+        """Run one of this worker's methods on the worker thread.
+
+        Reached through a queued signal connection, so the serial I/O (and
+        its blocking reads) stays off the GUI thread.  Calling the methods
+        directly, as this app used to, executes them in the caller's thread
+        and freezes the UI for the duration.
+        """
+        try:
+            getattr(self, method_name)(*args)
+        except Exception as exc:
+            self.operation_complete.emit(False, str(exc))
+
     def set_frequency(self, freq: int):
         try:
             success = self.laser.set_frequency_hz(freq)
@@ -197,15 +211,13 @@ class LaserWorker(QObject):
             self.operation_complete.emit(False, str(e))
 
     def query_power(self):
-        try:
+        # HeliosLaser has no power query: the driver README advertises
-            power = self.laser.get_power_mw()
+        # get_power_mw(), but no such method exists and the protocol
-            if power is not None:
+        # mnemonic for an output-power read is not documented anywhere in
-                self.power_updated.emit(power)
+        # this repo.  This used to raise AttributeError into a popup.
-                self.operation_complete.emit(True, f"Power: {power:.2f} mW")
+        # See KNOWN_ISSUES.md — needs the command from the Helios manual.
-            else:
+        self.operation_complete.emit(
-                self.operation_complete.emit(False, "Failed to query power")
+            False, "Power query is not implemented (no known protocol command)")
-        except Exception as e:
-            self.operation_complete.emit(False, str(e))
 
     def query_enabled(self):
         try:
@@ -289,6 +301,9 @@ class LaserWorker(QObject):
 class HeliosTestApp(QMainWindow):
     """Main application window for Helios laser testing."""
 
+    # Dispatches a worker method name + args across the thread boundary.
+    worker_call = pyqtSignal(str, object)
+
     def __init__(self):
         super().__init__()
         self.laser = HeliosLaser()
@@ -586,6 +601,10 @@ class HeliosTestApp(QMainWindow):
         power_layout = QHBoxLayout()
 
         btn_get_power = QPushButton("Query Power")
+        btn_get_power.setEnabled(False)
+        btn_get_power.setToolTip(
+            "Not implemented: no documented Helios protocol command for "
+            "output power (see KNOWN_ISSUES.md).")
         btn_get_power.clicked.connect(self.on_query_power)
         power_layout.addWidget(btn_get_power)
 
@@ -697,6 +716,9 @@ class HeliosTestApp(QMainWindow):
             self.worker = LaserWorker(self.laser)
             self.worker_thread = QThread()
             self.worker.moveToThread(self.worker_thread)
+            # Queued (cross-thread) connection: the worker's methods run on
+            # the worker thread, not on whichever thread emits.
+            self.worker_call.connect(self.worker.invoke)
             self.worker.operation_complete.connect(self.on_operation_complete)
             self.worker.frequency_updated.connect(self.on_frequency_updated)
             self.worker.current_updated.connect(self.on_current_updated)
@@ -713,11 +735,27 @@ class HeliosTestApp(QMainWindow):
         else:
             QMessageBox.critical(self, "Connection Error", f"Failed to connect to {port}")
 
+    def _require_connection(self) -> bool:
+        """Warn and return False when no laser is connected."""
+        if self.laser.is_connected and self.worker is not None:
+            return True
+        QMessageBox.warning(self, "Error", "Not connected to laser")
+        return False
+
+    def _call_worker(self, method_name: str, *args):
+        """Run a worker method on the worker thread via a queued signal."""
+        if self.worker is not None:
+            self.worker_call.emit(method_name, args)
+
     def disconnect_laser(self):
         """Disconnect from the laser."""
         if self.worker_thread:
             self.worker_thread.quit()
-            self.worker_thread.wait()
+            self.worker_thread.wait(2000)
+        # Drop both references: a reconnect used to leak the previous
+        # QThread, worker, and all nine signal connections.
+        self.worker = None
+        self.worker_thread = None
 
         self.laser.disconnect()
         self.lbl_status.setText("Status: Disconnected")
@@ -729,137 +767,121 @@ class HeliosTestApp(QMainWindow):
 
     def on_set_frequency(self):
         """Set the laser frequency."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
         freq = self.spin_frequency.value()
-        self.worker.set_frequency(freq)
+        self._call_worker("set_frequency", freq)
 
     def on_query_frequency(self):
         """Query the laser frequency."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
-        self.worker.query_frequency()
+        self._call_worker("query_frequency")
 
     def on_set_current(self):
         """Set the laser current."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
         current = self.spin_current.value()
-        self.worker.set_current(current)
+        self._call_worker("set_current", current)
 
     def on_query_current(self):
         """Query the laser current."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
-        self.worker.query_current()
+        self._call_worker("query_current")
 
     def on_set_mode(self):
         """Set the laser pulse mode."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
         mode = self.combo_mode.currentData()
-        self.worker.set_pulse_mode(mode)
+        self._call_worker("set_pulse_mode", mode)
 
     def on_enable_laser(self):
         """Enable the laser."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
-        self.worker.set_laser_enable(True)
+        self._call_worker("set_laser_enable", True)
 
     def on_disable_laser(self):
         """Disable the laser."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
-        self.worker.set_laser_enable(False)
+        self._call_worker("set_laser_enable", False)
 
     def on_query_enabled(self):
         """Query if laser is enabled."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
-        self.worker.query_enabled()
+        self._call_worker("query_enabled")
 
     def on_query_power(self):
         """Query the laser output power."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
-        self.worker.query_power()
+        self._call_worker("query_power")
 
     def on_query_all(self):
         """Query all laser parameters."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
 
-        self.worker.query_serials()
+        self._call_worker("query_serials")
-        self.worker.query_frequency()
+        self._call_worker("query_frequency")
-        self.worker.query_current()
+        self._call_worker("query_current")
-        self.worker.query_power()
+        self._call_worker("query_power")
-        self.worker.query_enabled()
+        self._call_worker("query_enabled")
-        self.worker.query_status_registers()
+        self._call_worker("query_status_registers")
-        self.worker.query_remote_enable()
+        self._call_worker("query_remote_enable")
 
     def on_query_status(self):
         """Query LER/LCE/CCE status registers."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
-        self.worker.query_status_registers()
+        self._call_worker("query_status_registers")
 
     def on_reset_faults(self):
         """Send the fault reset sequence."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
-        self.worker.do_reset_faults()
+        self._call_worker("do_reset_faults")
 
     def on_query_remote_enable(self):
         """Query the remote enable (LRE) state."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
-        self.worker.query_remote_enable()
+        self._call_worker("query_remote_enable")
 
     def on_set_remote_enable(self, enable: bool):
         """Set the remote enable (LRE) state."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
-        self.worker.set_remote_enable(enable)
+        self._call_worker("set_remote_enable", enable)
 
     def on_ler_reset(self):
         """Send LER 0 only."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
-        self.worker.do_ler_reset()
+        self._call_worker("do_ler_reset")
 
     def on_send_raw(self):
         """Send the raw command from the terminal input."""
-        if not self.laser.is_connected:
+        if not self._require_connection():
-            QMessageBox.warning(self, "Error", "Not connected to laser")
             return
         cmd = self.le_raw_cmd.text().strip()
         if not cmd:
             return
-        self.worker.send_raw(cmd)
+        self._call_worker("send_raw", cmd)
 
     def on_raw_response(self, cmd: str, response: str):
         """Display raw TX/RX pair in the terminal log."""

sc3_aui_app.py

@@ -5,7 +5,6 @@ Loads sc3-aui-main.ui, sc3-aui-camera.ui, sc3-aui-scanprogress.ui via uic
 and wires up T3R, BBD202, oscilloscope, and camera hardware workers.
 """
 
-import queue
 import struct
 import sys
 import time
@@ -14,7 +13,7 @@ from threading import Thread
 
 import numpy as np
 from PyQt6 import uic
-from PyQt6.QtCore import QObject, QThread, QTimer, Qt, pyqtSignal, pyqtSlot
+from PyQt6.QtCore import QObject, QThread, QTimer, Qt, pyqtSignal
 from PyQt6.QtGui import QImage, QPixmap
 from PyQt6.QtWidgets import (
     QApplication, QDialog, QDialogButtonBox, QFileDialog, QHBoxLayout, QLabel,
@@ -38,6 +37,7 @@ from core.scan_resume import is_compatible, plan_resume
 from core.scope_sras import SAMPLE_RATE_HZ, configure_channels
 from core.sras_format import SCAN_CHANNELS, SrasFile, plan_from_header
 from gui.qt_t3r import QtT3RAdapter
+from gui.qt_workers import PollingQueueWorker, QueueWorker
 from gui.scan_bridge import QtScanController
 from hardware.helios_laser import HeliosLaser
 from hardware.pybbd202 import AXIS_X, AXIS_Y, ThorlabsServoDriver
@@ -53,7 +53,13 @@ BBD_DEFAULT_JOG_MM  = 0.5       # default jog step for BBD202
 
 
 class DCBiasImageWidget(FigureCanvas):
-    """Live 2D DC-bias image: rows × frames, matching sras_viewer's compute_dc_image view."""
+    """Live 2D DC-bias image: rows × frames, matching the viewer's DC image.
+
+    The image buffer is allocated once per scan and updated in place.  The
+    previous version rebuilt the whole array and the entire matplotlib
+    artist tree on every row, so the live preview got steadily slower as a
+    scan progressed (O(rows²) work for one scan).
+    """
 
     def __init__(self, parent=None):
         fig = Figure(tight_layout=True)
@@ -65,36 +71,59 @@ class DCBiasImageWidget(FigureCanvas):
             QSizePolicy.Policy.Expanding,
         )
         self.ax = fig.add_subplot(111)
-        self._row_data: list[np.ndarray] = []
+        self._img: np.ndarray | None = None
         self._im = None
-        self.ax.set_title("DC Bias Preview (ADC counts)")
+        self._placeholder = None
-        self.ax.set_xlabel("Frame")
+        self._reset_axes()
-        self.ax.set_ylabel("Row")
-        self.ax.text(0.5, 0.5, "Waiting for data…",
-                     transform=self.ax.transAxes, ha="center", va="center", color="gray")
-        self.draw()
-
-    def add_row(self, row_index: int, values):
-        """Store per-frame DC mean values for row_index (1-based) and refresh the image."""
-        idx = row_index - 1
-        while len(self._row_data) <= idx:
-            self._row_data.append(np.empty(0, dtype=np.float32))
-        self._row_data[idx] = np.asarray(values, dtype=np.float32)
-
-        # Build rectangular image — pad shorter rows with NaN so they render distinctly
-        max_len = max(len(r) for r in self._row_data)
-        img = np.full((len(self._row_data), max_len), np.nan, dtype=np.float32)
-        for i, row in enumerate(self._row_data):
-            img[i, :len(row)] = row
 
+    def _reset_axes(self):
         self.ax.clear()
         self.ax.set_title("DC Bias Preview (ADC counts)")
         self.ax.set_xlabel("Frame")
         self.ax.set_ylabel("Row")
-        self.ax.imshow(
+        self._placeholder = self.ax.text(
-            img, aspect="auto", origin="upper",
+            0.5, 0.5, "Waiting for data…", transform=self.ax.transAxes,
+            ha="center", va="center", color="gray")
+        self._im = None
+        self.draw_idle()
+
+    def begin_scan(self, n_rows: int, n_frames: int):
+        """Preallocate the image for a scan of this shape."""
+        self._img = np.full((max(1, n_rows), max(1, n_frames)), np.nan,
+                            dtype=np.float32)
+        self._reset_axes()
+
+    def add_row(self, row_index: int, values):
+        """Store per-frame DC means for row_index (1-based) and refresh."""
+        row = np.asarray(values, dtype=np.float32)
+        idx = row_index - 1
+
+        # Grow only if the scan turned out taller/wider than announced.
+        if self._img is None:
+            self.begin_scan(idx + 1, len(row))
+        if idx >= self._img.shape[0] or len(row) > self._img.shape[1]:
+            grown = np.full((max(idx + 1, self._img.shape[0]),
+                             max(len(row), self._img.shape[1])),
+                            np.nan, dtype=np.float32)
+            grown[:self._img.shape[0], :self._img.shape[1]] = self._img
+            self._img = grown
+            self._im = None      # extent changed; rebuild the artist once
+
+        self._img[idx, :len(row)] = row
+
+        if self._im is None:
+            if self._placeholder is not None:
+                self._placeholder.remove()
+                self._placeholder = None
+            self._im = self.ax.imshow(
+                self._img, aspect="auto", origin="upper",
                 cmap="viridis", interpolation="nearest",
             )
+        else:
+            self._im.set_data(self._img)
+            finite = self._img[np.isfinite(self._img)]
+            if finite.size:
+                self._im.set_clim(float(finite.min()), float(finite.max()))
         self.draw_idle()
 
 
@@ -103,61 +132,35 @@ BBD_JOG_ACCEL_MM_S2 = 50.0
 
 # ── BBD202 worker ─────────────────────────────────────────────────────────────
 
-class BBD202Worker(QObject):
+class BBD202Worker(PollingQueueWorker):
     """Manages ThorlabsServoDriver (MLS203-1) in a worker thread."""
-    connected        = pyqtSignal()
-    disconnected     = pyqtSignal()
-    connection_failed = pyqtSignal(str)
     position_updated = pyqtSignal(float, float)   # x_mm, y_mm
     homed_status     = pyqtSignal(bool, bool)     # x_homed, y_homed
-    error_occurred   = pyqtSignal(str)
+
+    POLL_INTERVAL_S = 0.2
 
     def __init__(self):
-        super().__init__()
+        super().__init__(poll_interval_s=self.POLL_INTERVAL_S)
         self.controller: ThorlabsServoDriver | None = None
-        self._cmd_q: queue.Queue = queue.Queue()
+        self.scanning_active = False   # pause polling during a scan
-        self._running = False
-        self.is_connected = False
-        self.scanning_active = False   # pause polling during scan
         self._jog_step = BBD_DEFAULT_JOG_MM
-        self._last_x: float | None = None
+        self._last_pos: tuple[float, float] | None = None
-        self._last_y: float | None = None
+        self._last_homed: tuple[bool, bool] | None = None
-        self._last_xh: bool | None = None
+        self._handlers.update({
-        self._last_yh: bool | None = None
+            "connect": self._do_connect,
-        self._last_poll_t = 0.0
+            "disconnect": self._do_disconnect,
+            "jog": self._do_jog,
+            "home_all": self._do_home_all,
+            "enable_all": self._do_enable_all,
+        })
 
-    @pyqtSlot()
+    def _on_stop(self):
-    def run(self):
-        self._running = True
-        while self._running:
-            try:
-                cmd = self._cmd_q.get(timeout=0.05)
-                self._dispatch(cmd)
-            except queue.Empty:
-                pass
-            if self.is_connected and self.controller and not self.scanning_active:
-                self._poll()
         if self.controller:
             try:
                 self.controller.disconnect()
             except Exception:
                 pass
 
-    def _dispatch(self, cmd: dict):
-        t = cmd["type"]
-        if t == "connect":
-            self._do_connect(cmd["port"])
-        elif t == "disconnect":
-            self._do_disconnect()
-        elif t == "jog":
-            self._do_jog(cmd["axis"], cmd["direction"])
-        elif t == "home_all":
-            self._do_home_all()
-        elif t == "enable_all":
-            self._do_enable_all()
-        elif t == "stop":
-            self._running = False
-
     def _do_connect(self, port: str):
         try:
             self.controller = ThorlabsServoDriver()
@@ -173,10 +176,12 @@ class BBD202Worker(QObject):
                                                 acceleration=BBD_JOG_ACCEL_MM_S2)
             self.is_connected = True
             self.connected.emit()
+            self.start_polling()
         except Exception as e:
             self.connection_failed.emit(str(e))
 
     def _do_disconnect(self):
+        self.stop_polling()
         if self.controller:
             try:
                 self.controller.disconnect()
@@ -194,8 +199,6 @@ class BBD202Worker(QObject):
             self.controller.move_axis_relative(dest, self._jog_step * direction, timeout=2.0)
         except TimeoutError:
             pass
-        except Exception as e:
-            self.error_occurred.emit(str(e))
 
     def _do_home_all(self):
         if not self.controller:
@@ -214,79 +217,54 @@ class BBD202Worker(QObject):
         self.controller.toggle_enabled_state(AXIS_X)
         self.controller.toggle_enabled_state(AXIS_Y)
 
-    def _poll(self):
+    def _poll_once(self):
-        now = time.time()
+        """Emit position/homed updates, but only when they actually change."""
-        if now - self._last_poll_t < 0.2:
+        if self.scanning_active or not self.controller:
             return
-        self._last_poll_t = now
         try:
-            x = self.controller.positions[0]
+            pos = (self.controller.positions[0], self.controller.positions[1])
-            y = self.controller.positions[1]
+            if pos != self._last_pos:
-            if x != self._last_x or y != self._last_y:
+                self._last_pos = pos
-                self._last_x = x
+                self.position_updated.emit(*pos)
-                self._last_y = y
+            homed = (self.controller.am_homed[0], self.controller.am_homed[1])
-                self.position_updated.emit(x, y)
+            if homed != self._last_homed:
-            xh = self.controller.am_homed[0]
+                self._last_homed = homed
-            yh = self.controller.am_homed[1]
+                self.homed_status.emit(*homed)
-            if xh != self._last_xh or yh != self._last_yh:
-                self._last_xh = xh
-                self._last_yh = yh
-                self.homed_status.emit(xh, yh)
         except Exception:
             pass
 
     # ── Queue API ─────────────────────────────────────────────────────────────
 
     def queue_connect(self, port: str):
-        self._cmd_q.put({"type": "connect", "port": port})
+        self._enqueue("connect", port=port)
 
     def queue_disconnect(self):
-        self._cmd_q.put({"type": "disconnect"})
+        self._enqueue("disconnect")
 
     def queue_jog(self, axis: str, direction: int):
-        self._cmd_q.put({"type": "jog", "axis": axis, "direction": direction})
+        self._enqueue("jog", axis=axis, direction=direction)
 
     def queue_home_all(self):
-        self._cmd_q.put({"type": "home_all"})
+        self._enqueue("home_all")
 
     def queue_enable_all(self):
-        self._cmd_q.put({"type": "enable_all"})
+        self._enqueue("enable_all")
-
-    def stop_worker(self):
-        self._cmd_q.put({"type": "stop"})
 
 
 # ── Oscilloscope worker ───────────────────────────────────────────────────────
 
-class OscopeWorker(QObject):
+class OscopeWorker(QueueWorker):
     """Manages TektronixOscilloscopeBase in a worker thread."""
-    connected        = pyqtSignal()
-    disconnected     = pyqtSignal()
-    connection_failed = pyqtSignal(str)
-    error_occurred   = pyqtSignal(str)
 
     def __init__(self):
         super().__init__()
         self.scope: TektronixOscilloscopeBase | None = None
-        self._cmd_q: queue.Queue = queue.Queue()
+        self._handlers.update({
-        self._running = False
+            "connect": self._do_connect,
-        self.is_connected = False
+            "disconnect": self._do_disconnect,
+        })
 
-    @pyqtSlot()
+    def _on_stop(self):
-    def run(self):
-        self._running = True
-        while self._running:
-            try:
-                cmd = self._cmd_q.get(timeout=0.1)
-                t = cmd["type"]
-                if t == "connect":
-                    self._do_connect(cmd["ip"])
-                elif t == "disconnect":
-                    self._do_disconnect()
-                elif t == "stop":
-                    self._running = False
-            except queue.Empty:
-                pass
         if self.scope:
             try:
                 self.scope.disconnect()
@@ -314,67 +292,48 @@ class OscopeWorker(QObject):
         self.disconnected.emit()
 
     def queue_connect(self, ip: str):
-        self._cmd_q.put({"type": "connect", "ip": ip})
+        self._enqueue("connect", ip=ip)
 
     def queue_disconnect(self):
-        self._cmd_q.put({"type": "disconnect"})
+        self._enqueue("disconnect")
-
-    def stop_worker(self):
-        self._cmd_q.put({"type": "stop"})
 
 
 # ── Helios laser worker ───────────────────────────────────────────────────────
 
-class HeliosWorker(QObject):
+class HeliosWorker(PollingQueueWorker):
-    """Manages HeliosLaser in a worker thread using a command queue."""
+    """Manages HeliosLaser in a worker thread using a command queue.
-    connected                = pyqtSignal()
+
-    disconnected             = pyqtSignal()
+    Status polling is self-rescheduling: the next poll is queued only once
-    connection_failed        = pyqtSignal(str)
+    the previous completes.  A free-running 1 s timer used to queue a ~2 s
+    job, so the queue grew without bound and the panel fell further behind
+    the longer it stayed connected.
+    """
     enabled_updated          = pyqtSignal(bool)
     current_updated          = pyqtSignal(int)
     diode_temp_updated       = pyqtSignal(float)
     pstage_temp_updated      = pyqtSignal(float)
     qswitch_temp_updated     = pyqtSignal(float)
     status_registers_updated = pyqtSignal(object, object, object)  # LER, LCE, CCE (int|None)
-    error_occurred           = pyqtSignal(str)
+
+    POLL_INTERVAL_S = 1.0
 
     def __init__(self):
-        super().__init__()
+        super().__init__(poll_interval_s=self.POLL_INTERVAL_S)
         self._laser: HeliosLaser | None = None
-        self._cmd_q: queue.Queue = queue.Queue()
+        self._handlers.update({
-        self._running = False
+            "connect": self._do_connect,
-        self.is_connected = False
+            "disconnect": self._do_disconnect,
+            "set_enable": self._do_set_enable,
+            "set_current": self._do_set_current,
+        })
 
-    @pyqtSlot()
+    def _on_stop(self):
-    def run(self):
-        self._running = True
-        while self._running:
-            try:
-                cmd = self._cmd_q.get(timeout=0.1)
-                self._dispatch(cmd)
-            except queue.Empty:
-                pass
         if self._laser:
             try:
                 self._laser.disconnect()
             except Exception:
                 pass
 
-    def _dispatch(self, cmd: dict):
-        t = cmd["type"]
-        if t == "connect":
-            self._do_connect(cmd["port"])
-        elif t == "disconnect":
-            self._do_disconnect()
-        elif t == "set_enable":
-            self._do_set_enable(cmd["enable"])
-        elif t == "set_current":
-            self._do_set_current(cmd["current_ma"])
-        elif t == "poll_status":
-            self._do_poll_status()
-        elif t == "stop":
-            self._running = False
-
     def _do_connect(self, port: str):
         try:
             self._laser = HeliosLaser(timeout=1.0)
@@ -384,12 +343,13 @@ class HeliosWorker(QObject):
                 return
             self.is_connected = True
             self.connected.emit()
-            self._do_poll_status()
+            self.start_polling()
         except Exception as e:
             self._laser = None
             self.connection_failed.emit(str(e))
 
     def _do_disconnect(self):
+        self.stop_polling()
         if self._laser:
             try:
                 self._laser.set_laser_enable(False)
@@ -406,75 +366,52 @@ class HeliosWorker(QObject):
     def _do_set_enable(self, enable: bool):
         if not self._laser:
             return
-        try:
         self._laser.set_laser_enable(enable)
         self.enabled_updated.emit(self._laser.is_laser_enabled())
-        except Exception as e:
-            self.error_occurred.emit(str(e))
 
     def _do_set_current(self, current_ma: int):
         if not self._laser:
             return
-        try:
         self._laser.set_current_ma(current_ma)
         self.current_updated.emit(current_ma)
-        except Exception as e:
-            self.error_occurred.emit(str(e))
 
-    def _do_poll_status(self):
+    def _poll_once(self):
+        """Read the full status set.  Individual reads are allowed to fail
+        (a timed-out register shouldn't suppress the rest of the panel)."""
         if not self._laser or not self._laser.is_connected:
             return
         try:
-            ler, lce, cce = self._laser.get_status_registers()
+            self.status_registers_updated.emit(*self._laser.get_status_registers())
-            self.status_registers_updated.emit(ler, lce, cce)
         except Exception:
             pass
         try:
             self.enabled_updated.emit(self._laser.is_laser_enabled())
         except Exception:
             pass
+        for getter, signal in (
+            (self._laser.get_current_ma, self.current_updated),
+            (self._laser.get_diode_temp_c, self.diode_temp_updated),
+            (self._laser.get_power_stage_temp_c, self.pstage_temp_updated),
+            (self._laser.get_qswitch_temp_c, self.qswitch_temp_updated),
+        ):
             try:
-            current = self._laser.get_current_ma()
+                value = getter()
-            if current is not None:
+                if value is not None:
-                self.current_updated.emit(current)
+                    signal.emit(value)
-        except Exception:
-            pass
-        try:
-            t = self._laser.get_diode_temp_c()
-            if t is not None:
-                self.diode_temp_updated.emit(t)
-        except Exception:
-            pass
-        try:
-            t = self._laser.get_power_stage_temp_c()
-            if t is not None:
-                self.pstage_temp_updated.emit(t)
-        except Exception:
-            pass
-        try:
-            t = self._laser.get_qswitch_temp_c()
-            if t is not None:
-                self.qswitch_temp_updated.emit(t)
             except Exception:
                 pass
 
     def queue_connect(self, port: str):
-        self._cmd_q.put({"type": "connect", "port": port})
+        self._enqueue("connect", port=port)
 
     def queue_disconnect(self):
-        self._cmd_q.put({"type": "disconnect"})
+        self._enqueue("disconnect")
 
     def queue_set_enable(self, enable: bool):
-        self._cmd_q.put({"type": "set_enable", "enable": enable})
+        self._enqueue("set_enable", enable=enable)
 
     def queue_set_current(self, current_ma: int):
-        self._cmd_q.put({"type": "set_current", "current_ma": current_ma})
+        self._enqueue("set_current", current_ma=current_ma)
-
-    def queue_poll_status(self):
-        self._cmd_q.put({"type": "poll_status"})
-
-    def stop_worker(self):
-        self._cmd_q.put({"type": "stop"})
 
 
 # ── Camera window popup ───────────────────────────────────────────────────────
@@ -633,17 +570,13 @@ class HeliosWindow(QWidget):
         self.setWindowTitle("Helios Laser")
 
         self._worker = worker
-
+        # Polling is driven by the worker itself (self-rescheduling), so
-        self._poll_timer = QTimer(self)
+        # there is no timer here to outpace the device.
-        self._poll_timer.setInterval(1000)
-        self._poll_timer.timeout.connect(self._worker.queue_poll_status)
-
         self._wire_signals()
         self._update_controls(False)
         self._set_emission_indicator(False)
 
     def closeEvent(self, event):
-        self._poll_timer.stop()
         if self._worker.is_connected:
             self._worker.queue_disconnect()
         super().closeEvent(event)
@@ -683,7 +616,6 @@ class HeliosWindow(QWidget):
             DEFAULTS.save()
             self._worker.queue_connect(port)
         else:
-            self._poll_timer.stop()
             self._worker.queue_disconnect()
 
     def _on_connected(self):
@@ -691,10 +623,8 @@ class HeliosWindow(QWidget):
         self.helios_connect_toggle.setText("Disconnect")
         self.helios_status_label.setText("Connected")
         self._update_controls(True)
-        self._poll_timer.start()
 
     def _on_disconnected(self):
-        self._poll_timer.stop()
         self.helios_connect_toggle.blockSignals(True)
         self.helios_connect_toggle.setChecked(False)
         self.helios_connect_toggle.setText("Connect")
@@ -905,6 +835,10 @@ class ScanProgressWindow(QWidget):
     def update_dc_bias_plot(self, row: int, values):
         self.bias_image_widget.add_row(row, values)
 
+    def begin_scan(self, n_rows: int, n_frames: int):
+        """Size the DC preview for the scan about to run."""
+        self.bias_image_widget.begin_scan(n_rows, n_frames)
+
 
 # ── Scan worker ───────────────────────────────────────────────────────────────
 
@@ -1342,6 +1276,8 @@ class MainWindow(QMainWindow):
             0, plan.per_angle[ai0].n_rows,
             0 if resume is None else ai0 + 1, plan.n_angles
         )
+        self._scan_progress.begin_scan(plan.per_angle[ai0].n_rows,
+                                       plan.per_angle[ai0].n_frames)
         self._scan_progress.show()
         self._scan_thread.start()
 

tests/test_qt_workers.py

@@ -0,0 +1,172 @@
+"""gui.qt_workers: the shared queue/poll worker base."""
+import threading
+import time
+
+import pytest
+from PyQt6.QtCore import QThread
+from PyQt6.QtWidgets import QApplication
+
+from gui.qt_workers import PollingQueueWorker, QueueWorker
+
+
+@pytest.fixture(scope="module")
+def qapp():
+    yield QApplication.instance() or QApplication([])
+
+
+class _Recorder(QueueWorker):
+    def __init__(self):
+        super().__init__()
+        self.seen = []
+        self.stopped = threading.Event()
+        self._handlers.update({
+            "note": self._note,
+            "boom": self._boom,
+        })
+
+    def _note(self, value):
+        self.seen.append(value)
+
+    def _boom(self):
+        raise RuntimeError("handler failed")
+
+    def _on_stop(self):
+        self.stopped.set()
+
+
+def _run_until(worker, predicate, timeout=5.0):
+    """Run the worker loop on a plain thread until predicate() is true.
+
+    Pumps the Qt event loop while waiting: signals emitted from the worker
+    thread are delivered as queued events on this (main) thread.
+    """
+    app = QApplication.instance()
+    t = threading.Thread(target=worker.run, daemon=True)
+    t.start()
+    deadline = time.monotonic() + timeout
+    while not predicate() and time.monotonic() < deadline:
+        app.processEvents()
+        time.sleep(0.01)
+    app.processEvents()
+    return t
+
+
+def test_commands_dispatch_in_order(qapp):
+    w = _Recorder()
+    for i in range(5):
+        w._enqueue("note", value=i)
+    t = _run_until(w, lambda: len(w.seen) == 5)
+    w.stop_worker()
+    t.join(timeout=5)
+    assert w.seen == [0, 1, 2, 3, 4]
+    assert w.stopped.is_set()
+
+
+def test_handler_exception_is_reported_not_fatal(qapp):
+    w = _Recorder()
+    errors = []
+    w.error_occurred.connect(errors.append)
+    w._enqueue("boom")
+    w._enqueue("note", value="after")
+    t = _run_until(w, lambda: w.seen == ["after"])
+    w.stop_worker()
+    t.join(timeout=5)
+    assert w.seen == ["after"], "loop died on a failing handler"
+    assert errors and "handler failed" in errors[0]
+
+
+def test_unknown_command_reported(qapp):
+    w = _Recorder()
+    errors = []
+    w.error_occurred.connect(errors.append)
+    w._enqueue("nope")
+    t = _run_until(w, lambda: bool(errors))
+    w.stop_worker()
+    t.join(timeout=5)
+    assert errors and "Unknown command" in errors[0]
+
+
+def test_idle_worker_does_not_spin(qapp):
+    """The loop must block on the queue, not poll it on a timeout."""
+    w = _Recorder()
+    t = threading.Thread(target=w.run, daemon=True)
+    t.start()
+    time.sleep(0.3)                      # idle
+    cpu_before = time.process_time()
+    time.sleep(0.5)                      # still idle
+    cpu_used = time.process_time() - cpu_before
+    w.stop_worker()
+    t.join(timeout=5)
+    # A 10–20 Hz timeout-poll loop burns measurable CPU here; blocking uses ~0.
+    assert cpu_used < 0.05, f"idle worker used {cpu_used:.3f}s CPU"
+
+
+class _Poller(PollingQueueWorker):
+    def __init__(self):
+        super().__init__(poll_interval_s=0.02)
+        self.polls = 0
+        self.in_flight = 0
+        self.overlaps = 0
+        self.is_connected = True
+
+    def _poll_once(self):
+        self.in_flight += 1
+        if self.in_flight > 1:
+            self.overlaps += 1
+        time.sleep(0.05)      # deliberately slower than the poll interval
+        self.polls += 1
+        self.in_flight -= 1
+
+
+def test_polling_never_overlaps_or_backs_up(qapp):
+    """A device slower than the interval must not accumulate stale polls."""
+    w = _Poller()
+    t = threading.Thread(target=w.run, daemon=True)
+    t.start()
+    w.start_polling()
+    time.sleep(0.6)
+    w.stop_polling()
+    time.sleep(0.15)
+    queued = w._cmd_q.qsize()
+    w.stop_worker()
+    t.join(timeout=5)
+
+    assert w.polls >= 3, "polling did not run"
+    assert w.overlaps == 0, "polls overlapped"
+    # Self-rescheduling means at most one poll is ever pending.
+    assert queued <= 1, f"{queued} stale polls queued up"
+
+
+def test_stop_polling_halts_the_cycle(qapp):
+    w = _Poller()
+    t = threading.Thread(target=w.run, daemon=True)
+    t.start()
+    w.start_polling()
+    time.sleep(0.2)
+    w.stop_polling()
+    time.sleep(0.2)
+    settled = w.polls
+    time.sleep(0.2)
+    w.stop_worker()
+    t.join(timeout=5)
+    assert w.polls == settled, "polling continued after stop_polling()"
+
+
+def test_worker_runs_on_its_qthread(qapp):
+    """Sanity check the intended usage: run() executes on the QThread."""
+    w = _Recorder()
+    thread = QThread()
+    w.moveToThread(thread)
+    thread.started.connect(w.run)
+    ids = []
+    w._handlers["note"] = lambda value: ids.append(threading.get_ident())
+    thread.start()
+    w._enqueue("note", value=None)
+    deadline = time.monotonic() + 5
+    while not ids and time.monotonic() < deadline:
+        qapp.processEvents()
+        time.sleep(0.01)
+    w.stop_worker()
+    thread.quit()
+    assert thread.wait(5000)
+    assert ids and ids[0] != threading.get_ident()