bdwidth_status: keep a bdwidth USB dropout from shutting down Klipper

bdwidth reads its CH340 from a reactor timer without error handling, so
"write failed: [Errno 5] Input/output error" shut down Klipper mid print.
bdwidth_status now wraps the sensor's Read_bdwidth (bdwidth.py itself
unchanged): on a USB error it closes the port, reports once and returns
False, so bdwidth retries every 10 s; the port is reopened when the
device is back. New status fields usb_ok and usb_errors.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -50,7 +50,7 @@ everything below, grouped by topic. Comment out what you do not use there.
 | File | For |
 |---|---|
 | `xy_drift.py` | `AFC_XY_SAFETY_CHECK`: measures lost XY steps from the stepper step counts at the endstop triggers (CoreXY). The toolhead position after homing cannot show lost steps. |
-| `bdwidth_status.py` | exposes bdwidth's motion counter and width to macros |
+| `bdwidth_status.py` | exposes bdwidth's motion counter and width to macros, and keeps a USB dropout of bdwidth (port: usb) from shutting down Klipper: the read is retried every 10 s and the port reopened |
 | `bdpressure_check.py` | bd_pressure load check (`BDP_CHECK_START/STOP/QUERY`). Needs the load-check firmware from the bd_pressure `load-check-extension` branch; on stock firmware it reports "not available" and does nothing. |
 
 ### Scripts (`scripts/`)

extras/bdwidth_status.py

@@ -26,6 +26,19 @@
 #                    only starts reading on the first SET_BDWIDTH ... ENABLE
 #   linear_motion  - counts per mm (motion_linear_coefficient)
 #   sample_time    - seconds between sensor reads
+#   usb_ok         - False while the USB connection is down (port: usb)
+#   usb_errors     - USB read errors since Klipper start
+#
+# USB guard (port: usb): bdwidth reads the sensor from a reactor timer without
+# any error handling, so one USB dropout of its CH340 (write failed: [Errno 5]
+# Input/output error) shut down Klipper mid print. This module wraps the
+# sensor's Read_bdwidth at connect: on a USB error it closes the port, reports
+# it and returns False, after which bdwidth tries again 10 s later; the next
+# reads reopen the port (the /dev/serial/by-id path returns when the device
+# reconnects). bdwidth.py itself is not changed.
+
+
+import logging
 
 
 class BDWidthStatus:
@@ -34,11 +47,52 @@ class BDWidthStatus:
         self.name = config.get('sensor', 'fila_width_0')
         self.sensor_name = 'bdwidth ' + self.name
         self.sensor = None
+        self.usb_ok = True
+        self.usb_errors = 0
+        self._read = None
         self.printer.register_event_handler('klippy:connect',
                                             self._handle_connect)
 
     def _handle_connect(self):
         self.sensor = self.printer.lookup_object(self.sensor_name)
+        if (getattr(self.sensor, 'port', None) == 'usb'
+                and callable(getattr(self.sensor, 'Read_bdwidth', None))
+                and getattr(self.sensor, 'usb', None) is not None):
+            self._read = self.sensor.Read_bdwidth
+            self.sensor.Read_bdwidth = self._guarded_read
+            logging.info("bdwidth_status: USB guard active for %s", self.name)
+
+    def _respond(self, msg):
+        logging.warning(msg)
+        try:
+            self.printer.lookup_object('gcode').respond_info(msg)
+        except Exception:
+            pass
+
+    def _guarded_read(self):
+        # Called from bdwidth's reactor timer: must never raise
+        usb = self.sensor.usb
+        try:
+            if not usb.is_open:
+                usb.open()
+            result = self._read()
+        except Exception as e:
+            self.usb_errors += 1
+            try:
+                usb.close()
+            except Exception:
+                pass
+            if self.usb_ok:
+                self.usb_ok = False
+                self._respond("bdwidth %s: USB error (%s), print continues "
+                              "without width readings, retrying"
+                              % (self.name, e))
+            return False
+        if not self.usb_ok:
+            self.usb_ok = True
+            self._respond("bdwidth %s: USB connection restored after %d "
+                          "errors" % (self.name, self.usb_errors))
+        return result
 
     def get_status(self, eventtime):
         s = self.sensor
@@ -64,6 +118,8 @@ class BDWidthStatus:
             'active': str(getattr(s, 'is_active', 'disable')),
             'linear_motion': getattr(s, 'linear_motion', 42.8),
             'sample_time': getattr(s, 'sample_time', 1.),
+            'usb_ok': self.usb_ok,
+            'usb_errors': self.usb_errors,
         }