fan: Add support for heater_fan objects

Add support for fans designed to cool the components of an extruder or
heater.

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

config/example.cfg

@@ -322,3 +322,17 @@ max_z_accel: 30
 #   centripetal velocity cornering algorithm. A larger number will
 #   permit higher "cornering speeds" at the junction of two moves. The
 #   default is 0.02mm.
+
+# Heater cooling fans (one may define any number of sections with a
+# "heater_fan" prefix). A "heater fan" is a fan that will be enabled
+# whenever its associated heater is active.
+#[heater_fan my_nozzle_fan]
+# See the "fan" section for fan configuration parameters.
+#pin: ar7
+# The remaining variables are specific to heater_fan.
+#heater: extruder
+#   Name of the config section defining the heater that this fan is
+#   associated with.  The default is "extruder".
+#heater_temp: 50.0
+#   A temperature (in Celsius) that the heater must drop below before
+#   the fan is disabled. The default is 50 Celsius.

config/makergear-m2-2012.cfg

@@ -72,11 +72,14 @@ max_temp: 100
 [fan]
 pin: PH5
 
+[heater_fan nozzle_fan]
+pin: PH3
+max_power: 0.61
+hard_pwm: 1
+
 [mcu]
 serial: /dev/ttyACM0
 custom:
-  # Nozzle fan
-  set_pwm_out pin=PH3 cycle_ticks=1 value=155
   # Turn off yellow led
   set_digital_out pin=PB7 value=0
   # Stepper micro-step pins