Discover the Millennia eV port by its STM32 USB-CDC VID/PID

Problem: MillenniaEv25Device could only be constructed with an explicit
portPath; doInitializeDevice opened SerialPort(portPath=...) and never fell
back to VID/PID discovery, so a caller (e.g. the MillenniaUI app) had to know
the OS port name up front. The class did not set classIdVendor/classIdProduct,
so nothing identified the device by its USB descriptor.

Solution: Set classIdVendor = 0x0483 / classIdProduct = 0x5740 (the STM32
Virtual COM Port identity the lab eV25s enumerates as) and have
doInitializeDevice discover the port by that identity when no portPath is
given, mirroring FieldMasterDevice: it builds SerialPort(idVendor, idProduct,
serialNumber) -> matchAnyPort over pyserial's comports(), and raises a clear
UnableToInitialize naming the identity when nothing matches. An explicit
portPath still wins; a serialNumber narrows discovery when several STM32 CDC
ports are present. serialNumber is passed only when it actually narrows, so
matchPorts stays on its vid/pid path and never regex-matches a possibly-None
descriptor serial. The generic-STM32-VCP caveat is documented in the code.

DebugMillenniaEv25Device is unaffected: it overrides doInitializeDevice and
keeps its own fake identity. testMillennia.py passes (14 passed, 6 skipped).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dccote

hardwarelibrary/sources/millennia.py

@@ -31,20 +31,24 @@ class MillenniaEv25Device(LaserSourceDevice, OnOffControl, ShutterControl, Power
 
     # The lab eV25s enumerates its back-panel USB port as a native STM32
     # USB-CDC device: VID 0x0483, PID 0x5740 (confirmed on the bench, firmware
-    # SW214-00.004.096). MillenniaEv25Device is still instantiated by portPath
-    # (like CoboltDevice) rather than discovered by VID/PID, because 0x0483:0x5740
-    # is STMicroelectronics' *generic* STM32 Virtual COM Port identity, shared by
-    # many unrelated STM32-based USB-CDC boards; matching on it via
-    # SerialPort.matchAnyPort would risk binding to the wrong device. If a host
-    # only ever has this one STM32 CDC port, set classIdVendor = 0x0483 and
-    # classIdProduct = 0x5740 to enable discovery; otherwise pin the portPath.
-    # To re-derive on another unit:
+    # SW214-00.004.096). doInitializeDevice discovers the port by this identity
+    # when no portPath is given.
+    #
+    # Caveat: 0x0483:0x5740 is STMicroelectronics' *generic* STM32 Virtual COM
+    # Port identity, shared by many unrelated STM32-based USB-CDC boards. On a
+    # host that also has another STM32 CDC device, discovery could bind to the
+    # wrong port; pin it with an explicit portPath (or narrow with a
+    # serialNumber) in that case. A given portPath always wins over discovery.
+    # To re-derive the identity on another unit:
     #
     #   system_profiler SPUSBDataType | grep -A 12 -i millennia
     #   .venv/bin/python -c "from serial.tools.list_ports import comports; \
     #     [print(p.device, hex(p.vid or 0), hex(p.pid or 0), p.serial_number) \
     #      for p in comports()]"
 
+    classIdVendor = 0x0483   # STMicroelectronics
+    classIdProduct = 0x5740  # STM32 Virtual COM Port (generic STM32 CDC identity)
+
     defaultBaudRate = 115200
     commandTerminator = "\r"  # the eV accepts <CR>, <LF>, or both
     minPower = 0.05  # documented eV/Pro-s lower bound
@@ -76,8 +80,23 @@ def __init__(self, portPath=None, serialNumber=None, idProduct=None, idVendor=No
         self.laserSerialNumber = None
 
     def doInitializeDevice(self):
-        try:
+        if self.portPath is not None:
             self.port = SerialPort(portPath=self.portPath)
+        else:
+            # Discover by the STM32 USB-CDC identity. serialNumber is a regex
+            # (PhysicalDevice turns the default into ".*"); pass it only when it
+            # actually narrows, so SerialPort.matchPorts stays on its vid/pid
+            # path and never regex-matches against a possibly-None descriptor
+            # serial.
+            serialNumber = None if self.serialNumber in (None, ".*") else self.serialNumber
+            self.port = SerialPort(idVendor=self.idVendor, idProduct=self.idProduct,
+                                   serialNumber=serialNumber)
+            if self.port.portPath is None:
+                raise PhysicalDevice.UnableToInitialize(
+                    "No Millennia eV found by USB identity {0:#06x}:{1:#06x}. "
+                    "Pass an explicit portPath if several STM32 USB-CDC ports "
+                    "are present.".format(self.idVendor, self.idProduct))
+        try:
             self.port.open(baudRate=self.defaultBaudRate)
             self.readIdentity()
         except Exception as error: