heaters: Disable heater if it appears main thread has stopped updating

Update the heating code to periodically check that the main thread is
operating properly.  This is a mitigation for some rare cases where
the main thread may lockup while the background heater updating code
continues to run.  The goal is to detect these rare failures and
disable future heater updates.

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

klippy/extras/heaters.py

@@ -14,6 +14,7 @@
 MAX_HEAT_TIME = 5.0
 AMBIENT_TEMP = 25.
 PID_PARAM_BASE = 255.
+MAX_MAINTHREAD_TIME = 5.0
 
 class Heater:
     def __init__(self, config, sensor):
@@ -37,7 +38,7 @@ 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.verify_mainthread_time = -999.
         self.lock = threading.Lock()
         self.last_temp = self.smoothed_temp = self.target_temp = 0.
         self.last_temp_time = 0.
@@ -66,7 +67,7 @@ def __init__(self, config, sensor):
         self.printer.register_event_handler("klippy:shutdown",
                                             self._handle_shutdown)
     def set_pwm(self, read_time, value):
-        if self.target_temp <= 0. or self.is_shutdown:
+        if self.target_temp <= 0. or read_time > self.verify_mainthread_time:
             value = 0.
         if ((read_time < self.next_pwm_time or not self.last_pwm_value)
             and abs(value - self.last_pwm_value) < 0.05):
@@ -91,7 +92,7 @@ def temperature_callback(self, read_time, temp):
             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
+        self.verify_mainthread_time = -999.
     # External commands
     def get_name(self):
         return self.name
@@ -129,6 +130,9 @@ def alter_target(self, target_temp):
             target_temp = max(self.min_temp, min(self.max_temp, target_temp))
         self.target_temp = target_temp
     def stats(self, eventtime):
+        est_print_time = self.mcu_pwm.get_mcu().estimated_print_time(eventtime)
+        if not self.printer.is_shutdown():
+            self.verify_mainthread_time = est_print_time + MAX_MAINTHREAD_TIME
         with self.lock:
             target_temp = self.target_temp
             last_temp = self.last_temp