fan: Minor updates to tachometer handling

Add new fields to Command_Templates.md.

Remove unused self.rpm variable.

Use an explicit get_frequency() method in keeping with Klipper's
convention of not "peeking into member variables".

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

docs/Command_Templates.md

@@ -129,6 +129,10 @@ The following are common printer attributes:
   This is also available on "heater_fan", "fan_generic", and
   "controller_fan" config sections (eg,
   `printer["fan_generic my_fan"].speed`).
+- `printer.fan.rpm`: The measured fan speed in rotations per minute if
+  the fan has a tachometer_pin defined.  This is also available on
+  "heater_fan", "fan_generic", and "controller_fan" config sections
+  (eg, `printer["fan_generic my_fan"].rpm`).
 - `printer.gcode_move.gcode_position`: The current position of the
   toolhead relative to the current G-Code origin. That is, positions
   that one might directly send to a `G1` command. It is possible to

klippy/extras/fan.py

@@ -12,7 +12,6 @@ class Fan:
         self.printer = config.get_printer()
         self.last_fan_value = 0.
         self.last_fan_time = 0.
-        self.rpm = None
         # Read config
         self.max_power = config.getfloat('max_power', 1., above=0., maxval=1.)
         self.kick_start_time = config.getfloat('kick_start_time', 0.1,
@@ -84,8 +83,8 @@ class FanTachometer:
                 printer, pin, sample_time, poll_time)
 
     def get_status(self, eventtime):
-        if self._freq_counter:
-            rpm = self._freq_counter.frequency * 30. / self.ppr
+        if self._freq_counter is not None:
+            rpm = self._freq_counter.get_frequency() * 30. / self.ppr
         else:
             rpm = None
         return {'rpm': rpm}

klippy/extras/pulse_counter.py

@@ -74,6 +74,5 @@ class FrequencyCounter:
                 self._callback(time, self._freq)
         self._last_count = count
 
-    @property
-    def frequency(self):
+    def get_frequency(self):
         return self._freq