refactor: normalize data directory naming, and consolidate serial connection handling

src/pygui/backend/controllers/session_controller.py

@@ -309,9 +309,11 @@ class SessionController(QObject):
 
         # The new binary protocol sends payload of (sensorCount * 2) bytes
         # Each sensor is a big-endian 16-bit value (Sign-Magnitude).
+        expected_sensors = 80 if (family_code or "") == "X" else 244
+
         def parse_binary_frame(payload: bytes, seq: int) -> Frame:
             values = []
-            num_sensors = min(80, len(payload) // 2)
+            num_sensors = min(expected_sensors, len(payload) // 2)
             for i in range(num_sensors):
                 high_byte = payload[i * 2]
                 low_byte = payload[i * 2 + 1]
@@ -333,13 +335,9 @@ class SessionController(QObject):
         self._last = None
         self._last_raw_frame = None
 
-        try:
-            transport = pyserial.Serial(port, SerialPort.BAUDRATE, timeout=1)
-        except Exception as exc:
-            log.warning("Baud rate %d failed on %s, falling back to 115200: %s", SerialPort.BAUDRATE, port, exc)
-            transport = pyserial.Serial(port, 115200, timeout=1)
+        transport = SerialPort.open_port(port, timeout=1)
         # Send 'D2' command padded to 512 bytes to start the stream
-        cmd = b"D2" + (b"F" * 510)
+        cmd = b"D2" + SerialPort.COMMAND_PAD.encode()
         transport.write(cmd)
 
         def on_error(exc: Exception):

src/pygui/backend/data/constants.py

@@ -0,0 +1,3 @@
+# ===== Backend Data Constants =====
+
+DEFAULT_DATA_DIR_NAME = "isc_data"

src/pygui/backend/data/file_browser.py

@@ -10,6 +10,7 @@ from PySide6.QtWidgets import QFileDialog, QMessageBox
 
 from pygui.backend.data.csv_file_metadata import CSVFileMetadata
 from pygui.backend.wafer.zwafer_parser import ZWaferParser
+from pygui.backend.data.constants import DEFAULT_DATA_DIR_NAME
 
 
 # ===== File Browser Model =====
@@ -232,7 +233,7 @@ class FileBrowser(QObject):
             QStandardPaths.DocumentsLocation
         )
         base_dir = Path(documents_dir) if documents_dir else (Path.home() / "Documents")
-        return base_dir / "ISC_DATA"
+        return base_dir / DEFAULT_DATA_DIR_NAME
 
     def _set_current_directory(self, directory: Path) -> None:
         normalized = Path(directory)

src/pygui/backend/data/local_settings_model.py

@@ -7,6 +7,7 @@ from typing import Any
 from PySide6.QtCore import QObject, Property, QDateTime, QStandardPaths, Signal, Slot
 
 from pygui.backend.data.local_settings import LocalSettings
+from pygui.backend.data.constants import DEFAULT_DATA_DIR_NAME
 
 
 MASTER_FAMILIES = ("A", "B", "C", "D", "E", "F", "P", "X", "Z")
@@ -52,7 +53,7 @@ class LocalSettingsModel(QObject):
             QStandardPaths.DocumentsLocation
         )
         base_dir = Path(documents_dir) if documents_dir else (Path.home() / "Documents")
-        return base_dir / "ISC_DATA"
+        return base_dir / DEFAULT_DATA_DIR_NAME
 
     def _new_defaults(self) -> dict[str, Any]:
         return {

src/pygui/serialcomm/serial_port.py

@@ -45,6 +45,33 @@ class SerialPort:
     def __init__(self, port_name: str) -> None:
         self._port_name = port_name
 
+    # ------------------------------------------------------------------
+    # Port opening (shared between scoped and long-lived use)
+    # ------------------------------------------------------------------
+
+    @staticmethod
+    def open_port(port_name: str, timeout: float | None = None) -> pyserial.Serial:
+        """Open a serial port with baud-rate fallback.
+
+        Tries SerialPort.BAUDRATE first, falls back to 115200 on failure.
+        The caller owns the lifecycle of the returned Serial object."""
+        kwargs = dict(
+            parity=pyserial.PARITY_NONE,
+            bytesize=8,
+            stopbits=pyserial.STOPBITS_ONE,
+            xonxoff=False,
+            rtscts=False,
+            dsrdtr=False,
+        )
+        if timeout is not None:
+            kwargs["timeout"] = timeout
+
+        try:
+            return pyserial.Serial(port_name, SerialPort.BAUDRATE, **kwargs)
+        except Exception as exc:
+            log.warning("Baud rate %d failed on %s, falling back to 115200: %s", SerialPort.BAUDRATE, port_name, exc)
+            return pyserial.Serial(port_name, 115200, **kwargs)
+
     # ------------------------------------------------------------------
     # Context manager for scoped port access
     # ------------------------------------------------------------------
@@ -52,31 +79,7 @@ class SerialPort:
     @contextmanager
     def _open(self, timeout: float | None = None) -> Iterator[pyserial.Serial]:
         """Open the serial port, yield it, then close on exit."""
-        try:
-            port = pyserial.Serial(
-                self._port_name,
-                self.BAUDRATE,
-                parity=pyserial.PARITY_NONE,
-                bytesize=8,
-                stopbits=pyserial.STOPBITS_ONE,
-                xonxoff=False,
-                rtscts=False,
-                dsrdtr=False,
-            )
-        except Exception as exc:
-            log.warning("Baud rate %d failed on %s, falling back to 115200: %s", self.BAUDRATE, self._port_name, exc)
-            port = pyserial.Serial(
-                self._port_name,
-                115200,
-                parity=pyserial.PARITY_NONE,
-                bytesize=8,
-                stopbits=pyserial.STOPBITS_ONE,
-                xonxoff=False,
-                rtscts=False,
-                dsrdtr=False,
-            )
-        if timeout is not None:
-            port.timeout = timeout
+        port = self.open_port(self._port_name, timeout=timeout)
         try:
             yield port
         finally: