Add SerialPort.genericSerialConverterPorts to find USB/RS-232 adaptors

Problem: Instruments behind a generic RS-232/USB converter (FTDI, Prolific,
Silicon Labs CP210x, WCH CH34x) inherit the bridge's anonymous VID/PID and
have no identity of their own. SerialPort could match a known VID/PID/serial
(matchPorts) but had no way to list the generic-converter ports so a caller
could discover the candidate adaptors.

Solution: add genericSerialConverterVendors (VID -> chip name) plus two
classmethods: isGenericSerialConverter(idVendor) and
genericSerialConverterPorts(), which returns the connected ports whose vendor
is a known converter chip as pyserial ListPortInfo objects (open via .device,
disambiguate via .serial_number). Adds testSerialPortConverters.py, a
hardware-free test that mocks comports().

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

Author: dccote

hardwarelibrary/communication/serialport.py

@@ -17,7 +17,7 @@ class MoreThanOneMatch(serial.SerialException):
 class SerialPort(CommunicationPort):
     """
     An implementation of CommunicationPort using BSD-style serial port
-    
+
     Two strategies to initialize the SerialPort:
     1. with a portPath/port name (i.e. "COM1" or "/dev/cu.serial")
     2. with an instance of pyserial.Serial() that will support the same
@@ -26,6 +26,17 @@ class SerialPort(CommunicationPort):
        or the find_url.py script from the distribution. More info: https://eblot.github.io/pyftdi/api/usbtools.html
        You have to add any custom VID/PID when using tools (but they are added here in SerialPort) @line 30.
     """
+
+    # USB idVendor of the common, generic RS-232/USB serial-converter chips.
+    # A device behind one of these bridges inherits the bridge's anonymous
+    # VID/PID and carries no identity of its own, so it can only be told apart
+    # from other adaptors by its serial number. Extend as needed.
+    genericSerialConverterVendors = {
+        0x0403: "FTDI",
+        0x067b: "Prolific",
+        0x10c4: "Silicon Labs (CP210x)",
+        0x1a86: "WCH (CH340/CH341)",
+    }
     def __init__(self, idVendor=None, idProduct=None, serialNumber=None, portPath=None, port=None, delay=0):
         CommunicationPort.__init__(self)
 
@@ -138,6 +149,27 @@ def ftdiPorts(cls):
 
         return urls
 
+    @classmethod
+    def isGenericSerialConverter(cls, idVendor) -> bool:
+        """Whether idVendor belongs to a known generic USB/RS-232 converter
+        chip (FTDI, Prolific, Silicon Labs, WCH, ...). A None idVendor (a
+        non-USB port such as a Bluetooth channel) is not a converter."""
+        return idVendor in cls.genericSerialConverterVendors
+
+    @classmethod
+    def genericSerialConverterPorts(cls):
+        """Return the connected serial ports that come from a generic USB/RS-232
+        converter chip, as pyserial ListPortInfo objects.
+
+        Useful when the instrument at the other end has no USB identity of its
+        own (it sits behind an FTDI/Prolific/CP210x/CH34x cable): this lists the
+        candidate adaptors so the caller can pick one, typically by its
+        `serial_number`. Open a match with its `.device` path. The recognized
+        chips are in `genericSerialConverterVendors`; read a port's chip name
+        with `genericSerialConverterVendors[port.vid]`.
+        """
+        return [port for port in comports() if cls.isGenericSerialConverter(port.vid)]
+
     @property
     def isOpen(self):
         if self.port is None:

hardwarelibrary/tests/testSerialPortConverters.py

@@ -0,0 +1,51 @@
+import env
+import unittest
+from unittest.mock import patch
+
+from hardwarelibrary.communication.serialport import SerialPort
+
+
+class FakePort:
+    """Minimal stand-in for pyserial's ListPortInfo."""
+
+    def __init__(self, device, vid, pid=0x0001, serial_number="SN"):
+        self.device = device
+        self.vid = vid
+        self.pid = pid
+        self.serial_number = serial_number
+
+
+class TestIsGenericSerialConverter(unittest.TestCase):
+    def testKnownVendorsAreConverters(self):
+        for idVendor in (0x0403, 0x067b, 0x10c4, 0x1a86):
+            self.assertTrue(SerialPort.isGenericSerialConverter(idVendor))
+
+    def testUnknownVendorIsNotConverter(self):
+        self.assertFalse(SerialPort.isGenericSerialConverter(0x0483))  # STM32 CDC
+
+    def testNoneVendorIsNotConverter(self):
+        self.assertFalse(SerialPort.isGenericSerialConverter(None))
+
+
+class TestGenericSerialConverterPorts(unittest.TestCase):
+    def testFiltersToConvertersOnly(self):
+        fakePorts = [
+            FakePort("/dev/cu.usbserial-FTDI", 0x0403, 0x6001, "FTFDLOTS"),
+            FakePort("/dev/cu.usbserial-CP210", 0x10c4, 0xea60, "CP01"),
+            FakePort("/dev/cu.usbmodem-STM32", 0x0483, 0x5740, "STM"),
+            FakePort("/dev/cu.Bluetooth", None, None, None),
+        ]
+        with patch("hardwarelibrary.communication.serialport.comports", return_value=fakePorts):
+            found = SerialPort.genericSerialConverterPorts()
+
+        devices = [port.device for port in found]
+        self.assertEqual(devices, ["/dev/cu.usbserial-FTDI", "/dev/cu.usbserial-CP210"])
+
+    def testReturnsEmptyWhenNoConverters(self):
+        fakePorts = [FakePort("/dev/cu.usbmodem-STM32", 0x0483)]
+        with patch("hardwarelibrary.communication.serialport.comports", return_value=fakePorts):
+            self.assertEqual(SerialPort.genericSerialConverterPorts(), [])
+
+
+if __name__ == "__main__":
+    unittest.main()