error_mcu: Move shutdown error message formatting to new error_mcu.py module

Create a new module to help format verbose mcu error messages.  Move
the shutdown message formatting to this module.  This moves the error
formatting out of the background thread and out of the critical
shutdown code path.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/error_mcu.py

@@ -0,0 +1,67 @@
+# More verbose information on micro-controller errors
+#
+# Copyright (C) 2024  Kevin O'Connor <kevin@koconnor.net>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+import logging
+
+message_shutdown = """
+Once the underlying issue is corrected, use the
+"FIRMWARE_RESTART" command to reset the firmware, reload the
+config, and restart the host software.
+Printer is shutdown
+"""
+
+Common_MCU_errors = {
+    ("Timer too close",): """
+This often indicates the host computer is overloaded. Check
+for other processes consuming excessive CPU time, high swap
+usage, disk errors, overheating, unstable voltage, or
+similar system problems on the host computer.""",
+    ("Missed scheduling of next ",): """
+This is generally indicative of an intermittent
+communication failure between micro-controller and host.""",
+    ("ADC out of range",): """
+This generally occurs when a heater temperature exceeds
+its configured min_temp or max_temp.""",
+    ("Rescheduled timer in the past", "Stepper too far in past"): """
+This generally occurs when the micro-controller has been
+requested to step at a rate higher than it is capable of
+obtaining.""",
+    ("Command request",): """
+This generally occurs in response to an M112 G-Code command
+or in response to an internal error in the host software.""",
+}
+
+def error_hint(msg):
+    for prefixes, help_msg in Common_MCU_errors.items():
+        for prefix in prefixes:
+            if msg.startswith(prefix):
+                return help_msg
+    return ""
+
+class PrinterMCUError:
+    def __init__(self, config):
+        self.printer = config.get_printer()
+        self.printer.register_event_handler("klippy:notify_mcu_shutdown",
+                                            self._handle_notify_mcu_shutdown)
+    def _check_mcu_shutdown(self, msg, details):
+        mcu_name = details['mcu']
+        mcu_msg = details['reason']
+        event_type = details['event_type']
+        prefix = "MCU '%s' shutdown: " % (mcu_name,)
+        if event_type == 'is_shutdown':
+            prefix = "Previous MCU '%s' shutdown: " % (mcu_name,)
+        # Lookup generic hint
+        hint = error_hint(msg)
+        # Update error message
+        newmsg = "%s%s%s%s" % (prefix, mcu_msg, hint, message_shutdown)
+        self.printer.update_error_msg(msg, newmsg)
+    def _handle_notify_mcu_shutdown(self, msg, details):
+        if msg == "MCU shutdown":
+            self._check_mcu_shutdown(msg, details)
+        else:
+            self.printer.update_error_msg(msg, "%s%s" % (msg, message_shutdown))
+
+def load_config(config):
+    return PrinterMCUError(config)