heaters: Clarify reported stats after a shutdown

The pid logic can continue after a shutdown, even though the pin
commands sent to the mcu are ignored.  However, this behavior can
result in confusing "stats" messages in the log.  Explicitly disable
updates after a shutdown event so that the log statistics are more
clear.

Signed-off-by: Kevin O'Connor <[email protected]>

klippy/extras/heaters.py

@@ -37,6 +37,7 @@ def __init__(self, config, sensor):
         self.max_power = config.getfloat('max_power', 1., above=0., maxval=1.)
         self.smooth_time = config.getfloat('smooth_time', 1., above=0.)
         self.inv_smooth_time = 1. / self.smooth_time
+        self.is_shutdown = False
         self.lock = threading.Lock()
         self.last_temp = self.smoothed_temp = self.target_temp = 0.
         self.last_temp_time = 0.
@@ -62,8 +63,10 @@ def __init__(self, config, sensor):
         gcode.register_mux_command("SET_HEATER_TEMPERATURE", "HEATER",
                                    short_name, self.cmd_SET_HEATER_TEMPERATURE,
                                    desc=self.cmd_SET_HEATER_TEMPERATURE_help)
+        self.printer.register_event_handler("klippy:shutdown",
+                                            self._handle_shutdown)
     def set_pwm(self, read_time, value):
-        if self.target_temp <= 0.:
+        if self.target_temp <= 0. or self.is_shutdown:
             value = 0.
         if ((read_time < self.next_pwm_time or not self.last_pwm_value)
             and abs(value - self.last_pwm_value) < 0.05):
@@ -87,6 +90,8 @@ def temperature_callback(self, read_time, temp):
             self.smoothed_temp += temp_diff * adj_time
             self.can_extrude = (self.smoothed_temp >= self.min_extrude_temp)
         #logging.debug("temp: %.3f %f = %f", read_time, temp)
+    def _handle_shutdown(self):
+        self.is_shutdown = True
     # External commands
     def get_name(self):
         return self.name