refactor: implement thread-safe hardware operations, port caching, and refined state management in the device controller

src/pygui/ISC/Tabs/StatusTab.qml

@@ -109,12 +109,6 @@ ColumnLayout {
     function parseAndSavePendingRead() {
         deviceController.parseAndSaveData(root.currentFamilyCode(), deviceController.selectedPort || "");
     }
-    function getCsvFileName() {
-        var path = root.csvPath;
-        if (!path) return "";
-        var parts = path.split(/[\/\\]/);
-        return parts[parts.length - 1].toUpperCase();
-    }
 
     FolderDialog {
         id: saveDirDialog
@@ -300,34 +294,29 @@ ColumnLayout {
                         spacing: 2
 
                         Text {
-                            text: root.csvPath !== "" ? root.getCsvFileName() : "DIRECTORY"
+                            text: "DIRECTORY"
-                            color: root.csvPath !== "" ? Theme.headingColor : Theme.sideMutedText
+                            color: Theme.sideMutedText
-                            font.pixelSize: root.csvPath !== "" ? Theme.fontSm : Theme.fontMd
+                            font.pixelSize: Theme.fontMd
-                            font.weight: root.csvPath !== "" ? Font.Bold : Font.Medium
+                            font.weight: Font.Medium
-                            font.letterSpacing: root.csvPath !== "" ? 0 : 1.2
+                            font.letterSpacing: 1.2
                             font.family: Theme.uiFontFamily
-                            elide: Text.ElideRight
+                        }
+                        Text {
+                            text: deviceController.saveDataDir || "Not configured"
+                            color: Theme.bodyColor
+                            font.pixelSize: Theme.fontSm
+                            font.family: Theme.uiFontFamily
+                            font.italic: true
+                            opacity: 0.7
+                            elide: Text.ElideMiddle
                             Layout.fillWidth: true
                         }
                     }
 
-                    Item { Layout.fillHeight: true }
-
                     RowLayout {
                         Layout.fillWidth: true
                         spacing: 8
 
-                        Text {
-                            text: deviceController.saveDataDir || "Not configured"
-                            color: Theme.bodyColor
-                            font.pixelSize: Theme.fontXs
-                            font.family: Theme.uiFontFamily
-                            font.italic: true
-                            opacity: 0.6
-                            elide: Text.ElideMiddle
-                            Layout.fillWidth: true
-                        }
-
                         Rectangle {
                             visible: root.csvPath !== ""
                             width: sessionSavedLabel.implicitWidth + 12
@@ -349,6 +338,8 @@ ColumnLayout {
                             }
                         }
 
+                        Item { Layout.fillWidth: true }
+
                         Button {
                             id: browseBtn
                             text: "Save As"

src/pygui/backend/controllers/device_controller.py

@@ -39,6 +39,9 @@ class DeviceController(QObject):
 
     # ---- public signals ----
     portsUpdated = Signal(list)
+    connectionStatusChanged = Signal()
+    operationInProgressChanged = Signal()
+    selectedPortChanged = Signal()
     detectResult = Signal(object)  # WaferInfo dict or None
     readResult = Signal(dict)  # {"success": bool, "bytes": int} or {"error": str}
     eraseResult = Signal(dict)  # {"success": bool}
@@ -51,6 +54,8 @@ class DeviceController(QObject):
     # ---- private signals (marshal worker-thread results back to main thread) ----
     _detectFinished = Signal(object, object)     # (port_or_None, WaferInfo_or_None)
     _readFinished = Signal(str, str, object)     # (port, family_code, bytes_or_None)
+    _eraseFinished = Signal(bool)                # (success)
+    _debugFinished = Signal(dict)                # (result_dict)
 
     def __init__(self, settings: LocalSettings, data_dir: str, parent: QObject | None = None) -> None:
         super().__init__(parent)
@@ -79,6 +84,8 @@ class DeviceController(QObject):
         # Marshal worker-thread results onto the Qt main thread.
         self._detectFinished.connect(self._handle_detect_finished, Qt.ConnectionType.QueuedConnection)
         self._readFinished.connect(self._handle_read_finished, Qt.ConnectionType.QueuedConnection)
+        self._eraseFinished.connect(self._handle_erase_finished, Qt.ConnectionType.QueuedConnection)
+        self._debugFinished.connect(self._handle_debug_finished, Qt.ConnectionType.QueuedConnection)
 
         root_logger = logging.getLogger()
         root_logger.addHandler(QmlActivityLogHandler(self))
@@ -94,14 +101,14 @@ class DeviceController(QObject):
         """Update connection status and notify QML."""
         if self._connection_status != status:
             self._connection_status = status
-            self.portsUpdated.emit(self.availablePorts)
+            self.connectionStatusChanged.emit()
 
-    @Property(str, notify=portsUpdated)
+    @Property(str, notify=connectionStatusChanged)
     def connectionStatus(self) -> str:
         """Current connection status string for display."""
         return self._connection_status
 
-    @Property(bool, notify=portsUpdated)
+    @Property(bool, notify=operationInProgressChanged)
     def operationInProgress(self) -> bool:
         """Whether a hardware operation is currently running."""
         return self._operation_in_progress
@@ -119,7 +126,7 @@ class DeviceController(QObject):
         self._append_log(f"Save data dir set to: {path}")
         self._save_status()
 
-    @Property(str, notify=portsUpdated)
+    @Property(str, notify=selectedPortChanged)
     def selectedPort(self) -> str:
         """Currently selected serial port shared across the UI."""
         return self._selected_port
@@ -128,8 +135,10 @@ class DeviceController(QObject):
     @slot_error_boundary
     def setSelectedPort(self, port: str) -> None:
         """Set the active serial port from the port selector."""
-        self._selected_port = port
+        if self._selected_port != port:
-        self._save_status()
+            self._selected_port = port
+            self.selectedPortChanged.emit()
+            self._save_status()
 
     @Property(int, notify=parsedDataReady)
     def dataRowCount(self) -> int:
@@ -243,14 +252,10 @@ class DeviceController(QObject):
 
 
     def _set_operation_progress(self, in_progress: bool) -> None:
-        """Set operation progress state and notify QML.
+        """Set operation progress state and notify QML."""
-
+        if self._operation_in_progress != in_progress:
-        portsUpdated is the shared notify signal for availablePorts,
+            self._operation_in_progress = in_progress
-        connectionStatus, and operationInProgress — emitting it forces
+            self.operationInProgressChanged.emit()
-        QML to re-evaluate all three bindings.
-        """
-        self._operation_in_progress = in_progress
-        self.portsUpdated.emit(self._service.enumerate_ports())
 
     # ---- Public Slots ----
 
@@ -258,6 +263,7 @@ class DeviceController(QObject):
     @slot_error_boundary
     def refreshPorts(self) -> None:
         """Scan for available serial ports and emit updated list."""
+        self._service.clear_port_scan_cache()
         ports = self._service.enumerate_ports()
         self._set_connection_status("Disconnected")
         self.portsUpdated.emit(ports)
@@ -396,12 +402,33 @@ class DeviceController(QObject):
     @slot_error_boundary
     def eraseMemory(self, port: str) -> None:
         """Send p1 erase command."""
+        if self._operation_in_progress:
+            self._append_log("Already busy — ignoring erase request")
+            return
         self._set_operation_progress(True)
         self._set_connection_status("Erasing...")
         self.portsUpdated.emit(self._service.enumerate_ports())
         self._append_log(f"Erase command sent to {port} (wafer takes ~15s) ...")
 
-        ok = self._service.erase_wafer(port)
+        threading.Thread(
+            target=self._erase_worker,
+            args=(port,),
+            daemon=True,
+        ).start()
+
+    def _erase_worker(self, port: str) -> None:
+        """Background thread worker for eraseMemory."""
+        try:
+            ok = self._service.erase_wafer(port)
+        except Exception as exc:
+            log.exception("Erase worker crashed: %s", exc)
+            ok = False
+        self._eraseFinished.emit(ok)
+
+    @Slot(bool)
+    @slot_error_boundary
+    def _handle_erase_finished(self, ok: bool) -> None:
+        """Main thread completion handler for eraseMemory."""
         if ok:
             self._set_connection_status("Connected")
             self._append_log("Erase command accepted — wait ~15 seconds")
@@ -414,45 +441,63 @@ class DeviceController(QObject):
     @Slot(str)
     @slot_error_boundary
     def readDebug(self, port: str) -> None:
-        """Read both D1 (sensor) and F1 (debug/cold-junction) data.
+        """Read both D1 (sensor) and F1 (debug/cold-junction) data."""
-
+        if self._operation_in_progress:
-        Emits debugResult with counts on success.
+            self._append_log("Already busy — ignoring debug read request")
-        """
+            return
         self._set_operation_progress(True)
         self._set_connection_status("Reading debug...")
         self.portsUpdated.emit(self._service.enumerate_ports())
         self._append_log(f"Reading debug data on {port} ...")
 
-        # Step 1: D1 sensor data
+        threading.Thread(
-        sensor_data = self._service.read_wafer_data(port, family_code="")
+            target=self._debug_worker,
-        if sensor_data is None:
+            args=(port,),
+            daemon=True,
+        ).start()
+
+    def _debug_worker(self, port: str) -> None:
+        """Background thread worker for readDebug."""
+        try:
+            # Step 1: D1 sensor data
+            sensor_data = self._service.read_wafer_data(port, family_code="")
+            if sensor_data is None:
+                self._debugFinished.emit({"error": "D1 read failed"})
+                return
+
+            # Step 2: F1 debug data
+            debug_data = self._service.read_wafer_data(port, family_code="", cmd="F1")
+            if debug_data is None:
+                self._debugFinished.emit({"error": "F1 read failed"})
+                return
+
+            self._debugFinished.emit({
+                "success": True,
+                "sensor_bytes": len(sensor_data),
+                "debug_bytes": len(debug_data),
+            })
+        except Exception as exc:
+            log.exception("Debug worker crashed: %s", exc)
+            self._debugFinished.emit({"error": str(exc)})
+
+    @Slot(dict)
+    @slot_error_boundary
+    def _handle_debug_finished(self, result: dict) -> None:
+        """Main thread completion handler for readDebug."""
+        if result.get("success"):
+            self._set_connection_status("Connected")
+            sensor_bytes = result.get("sensor_bytes", 0)
+            debug_bytes = result.get("debug_bytes", 0)
+            self._append_log(
+                f"Debug read complete: {sensor_bytes} sensor bytes, "
+                f"{debug_bytes} debug bytes"
+            )
+        else:
             self._set_connection_status("Disconnected")
-            self._append_log("D1 read failed — aborting debug read")
+            err_msg = result.get("error", "Debug read failed")
-            self.debugResult.emit({"error": "D1 read failed"})
+            self._append_log(err_msg)
-            self._set_operation_progress(False)
-            return
 
-        self._append_log(f"D1 read: {len(sensor_data)} bytes")
+        self.debugResult.emit(result)
-
-        # Step 2: F1 debug data
-        debug_data = self._service.read_wafer_data(port, family_code="", cmd="F1")
-        if debug_data is None:
-            self._set_connection_status("Disconnected")
-            self._append_log("F1 read failed")
-            self.debugResult.emit({"error": "F1 read failed"})
-            self._set_operation_progress(False)
-            return
-
-        self._set_connection_status("Connected")
-        self._append_log(
-            f"Debug read complete: {len(sensor_data)} sensor bytes, "
-            f"{len(debug_data)} debug bytes"
-        )
-        self.debugResult.emit({
-            "success": True,
-            "sensor_bytes": len(sensor_data),
-            "debug_bytes": len(debug_data),
-        })
         self._set_operation_progress(False)
 
     @Slot(str, str)

src/pygui/backend/controllers/session_controller.py

@@ -232,7 +232,8 @@ class SessionController(QObject):
     def setMode(self, mode: str) -> None:
         if mode == self._mode:
             return
-        self.stopStream()
+        if mode != "live":
+            self.stopStream()
         self._play_timer.stop()
         self._mode = mode
         self.modeChanged.emit()
@@ -394,6 +395,9 @@ class SessionController(QObject):
     @Slot(str, str)
     @slot_error_boundary
     def startStream(self, port: str, family_code: str = "") -> None:
+        if self._reader is not None:
+            log.warning("startStream: StreamReader is already running.")
+            return
 
         from pygui.backend.wafer.wafer_layouts import load_layout_for_wafer_id
         from pygui.serialcomm.serial_port import SerialPort  # transport open
@@ -449,13 +453,24 @@ class SessionController(QObject):
         cmd = b"D2" + SerialPort.COMMAND_PAD.encode()
         transport.write(cmd)
 
+        import weakref
+        weak_self = weakref.ref(self)
+
         def on_error(exc: Exception):
             log.error("Live stream error: %s", exc)
-            self._liveError.emit()
+            ref = weak_self()
+            if ref is not None:
+                ref._liveError.emit()
+                ref.stopStream()
+
+        def on_frame(frame: Frame):
+            ref = weak_self()
+            if ref is not None:
+                ref._liveFrame.emit(frame)
 
         self._reader = StreamReader(
             transport, parse_binary_frame,
-            on_frame=lambda f: self._liveFrame.emit(f),
+            on_frame=on_frame,
             on_error=on_error,
             family_code=family_code or "A")
         self._reader.start()
@@ -474,10 +489,9 @@ class SessionController(QObject):
         self.liveStatsChanged.emit()
         if self._reader:
             transport = self._reader._transport
-            self._reader.stop()
-            self._reader = None
 
             # Send 'D2S' command padded to 512 bytes to stop the stream
+            # Send BEFORE stopping the reader which will close the port on thread exit
             if transport and transport.is_open:
                 try:
                     cmd = b"D2S" + (b"F" * 509)
@@ -486,6 +500,9 @@ class SessionController(QObject):
                 except Exception as exc:
                     log.error("Error sending stop command: %s", exc)
 
+            self._reader.stop()
+            self._reader = None
+
         self.stateChanged.emit()
         self.stopRecording()
 

src/pygui/serialcomm/data_parser.py

@@ -239,7 +239,7 @@ def remove_trailing_zeros(data: list[list[str]]) -> None:
                 fval = float(val)
             except ValueError:
                 fval = 99.9
-            if fval >= 0.01:
+            if abs(fval) >= 0.01:
                 is_all_zero = False
                 break
         if is_all_zero:

src/pygui/serialcomm/device_service.py

@@ -29,6 +29,12 @@ class DeviceService:
 
     def __init__(self, settings: LocalSettings) -> None:
         self._settings = settings
+        self._cached_ports: list[str] = []
+        self._last_port_scan_time = 0.0
+
+    def clear_port_scan_cache(self) -> None:
+        """Force the next scan to bypass the cache."""
+        self._last_port_scan_time = 0.0
 
     # ------------------------------------------------------------------
     # Public API
@@ -36,6 +42,11 @@ class DeviceService:
 
     def enumerate_ports(self) -> list[str]:
         """Return list of available serial port names."""
+        import time
+        now = time.monotonic()
+        if now - self._last_port_scan_time < 2.0:
+            return self._cached_ports
+
         hardware_ports = [p.device for p in serial.tools.list_ports.comports()]
         virtual_ports = []
 
@@ -86,6 +97,8 @@ class DeviceService:
             if p not in ordered_ports:
                 ordered_ports.append(p)
 
+        self._cached_ports = ordered_ports
+        self._last_port_scan_time = time.monotonic()
         return ordered_ports
 
 

src/pygui/serialcomm/stream_reader.py

@@ -36,17 +36,13 @@ class StreamReader:
     def _read_chunk(self, min_bytes: int = 1) -> bytes:
         """Read a chunk of available bytes from the transport.
 
-        Reads up to 256 bytes in one shot instead of byte-at-a-time,
+        Reads up to 256 bytes in one shot. If nothing is immediately
-        falling back to single-byte reads with a yield when nothing is
+        available, yields briefly to avoid a busy spin.
-        immediately available."""
+        """
         chunk = self._transport.read(max(min_bytes, 256))
-        if chunk:
+        if not chunk:
-            return chunk
-        # Nothing available right now – yield briefly to avoid busy-spin.
-        b = self._transport.read(1)
-        if not b:
             time.sleep(0.005)
-        return b
+        return chunk
 
     def _accumulate(self, needed: int) -> bytearray:
         """Accumulate *needed* bytes using buffered reads."""
@@ -92,6 +88,12 @@ class StreamReader:
 
             # Default: ASCII hex dump stream.
             self._run_ascii(raw)
+        except Exception as exc:
+            log.exception("StreamReader thread encountered error: %s", exc)
+            try:
+                self._on_error(exc)
+            except Exception:
+                pass
         finally:
             try:
                 self._transport.close()

tests/test_data_parser.py

@@ -242,6 +242,11 @@ class TestRemoveTrailingZeros:
         remove_trailing_zeros(data)
         assert len(data) == 2
 
+    def test_preserves_negative_temperatures(self):
+        data = [["25.0", "24.5"], ["-5.5", "-10.0"]]
+        remove_trailing_zeros(data)
+        assert len(data) == 2
+
 
 # ── save_to_csv ───────────────────────────────────────────────────────────────
 

tests/test_device_controller.py

@@ -87,31 +87,48 @@ def test_clear_session(controller):
     assert controller.selectedPort == ""
     assert controller.lastWaferInfo == ["", "", 0, "", 0, 0]
 
-def test_erase_memory(controller):
+def test_erase_memory_spawns_thread(controller):
-    controller._service.erase_wafer = MagicMock(return_value=True)
+    with patch("threading.Thread") as mock_thread:
+        controller.eraseMemory("COM1")
+        mock_thread.assert_called_once()
+        assert controller.operationInProgress
+
+def test_erase_memory_handler(controller):
     emitted_result = None
     def on_erase_result(result):
         nonlocal emitted_result
         emitted_result = result
 
     controller.eraseResult.connect(on_erase_result)
-    controller.eraseMemory("COM1")
+    controller._handle_erase_finished(True)
     assert emitted_result == {"success": True}
     assert controller.connectionStatus == "Connected"
+    assert not controller.operationInProgress
 
-def test_read_debug(controller):
+def test_read_debug_spawns_thread(controller):
-    controller._service.read_wafer_data = MagicMock(return_value=bytes([12] * 512))
+    with patch("threading.Thread") as mock_thread:
+        controller.readDebug("COM1")
+        mock_thread.assert_called_once()
+        assert controller.operationInProgress
+
+def test_read_debug_handler(controller):
     emitted_result = None
     def on_debug_result(result):
         nonlocal emitted_result
         emitted_result = result
 
     controller.debugResult.connect(on_debug_result)
-    controller.readDebug("COM1")
+    controller._handle_debug_finished({
+        "success": True,
+        "sensor_bytes": 512,
+        "debug_bytes": 512
+    })
     assert emitted_result is not None
     assert emitted_result.get("success") is True
     assert emitted_result.get("sensor_bytes") == 512
     assert emitted_result.get("debug_bytes") == 512
+    assert controller.connectionStatus == "Connected"
+    assert not controller.operationInProgress
 
 def test_parse_and_save_data_and_get_chart_data(controller):
     res = controller.getChartData()
@@ -187,3 +204,29 @@ def test_detect_wafer_clears_old_session(controller):
         assert len(controller._activity_log) == 1
         assert "Scanning all ports" in controller._activity_log[0]
 
+def test_device_service_port_caching(controller):
+    service = controller._service
+    # Mock comports list
+    with patch("serial.tools.list_ports.comports", return_value=[]), \
+         patch("subprocess.run") as mock_run:
+        # Mock subprocess to return empty
+        mock_run.return_value.returncode = 0
+        mock_run.return_value.stdout = ""
+
+        # Clear cache first
+        service.clear_port_scan_cache()
+
+        # First scan should invoke list_ports and subprocess
+        ports1 = service.enumerate_ports()
+        assert mock_run.call_count == 1
+
+        # Second scan within 2 seconds should return cached list without invoking subprocess
+        ports2 = service.enumerate_ports()
+        assert mock_run.call_count == 1
+        assert ports1 == ports2
+
+        # Clear cache and scan again should invoke subprocess
+        service.clear_port_scan_cache()
+        ports3 = service.enumerate_ports()
+        assert mock_run.call_count == 2
+