Allowed Disabling of Manager Timer

If so, the user will need to manually call the service_inputs() method
on a periodic basis.

Author: alanmitchell

README.md

@@ -32,7 +32,7 @@ Each Input object type has a number of configuration options, all with default v
 
 After the Manager object is created, it automatically starts polling the input objects at the default rate of 480 Hz (a 2x or greater multiple of 60 Hz will help 60 Hz noise to be filtered on Analog lines).  Each input is read and processed according to the type of input it is.
 
-At any time, the current values of all the inputs can be read by executing the `values()` method on the Manager object.  The return object is a superset of a Python dictionary, also allowing access to values through attributes:
+At any time, the current values of all the inputs can be read by executing the `values()` method on the Manager object.  The return object is a Python dictionary with the added feature that values can be read as attributes of the object:
 
 ```Python
 # get all of the current input values
@@ -103,6 +103,10 @@ Arguments include:
 
 `inputs`: This is the list of input objects that the Manager will periodically poll and manage.
 
-`timer_num`: The number of the microcontroller Timer that will be used to generate an interrupt for polling the inputs.
+`timer_num`: The number of the microcontroller Timer that will be used to generate an interrupt for polling the inputs.  If `None` is passed, no automatic polling of inputs will occur, and you will need to periodically call the `service_inputs()` method of this object, perhaps from your own Timer interrupt routine.
 
-`poll_freq`: The frequency that will be used to poll the inputs in Hz.  The default of 480 Hz will poll each sensor every 2.08 ms, which is a convenient value for debounce routines discussed later and analog averaging routines that sample across an exact number of 60 Hz cycles.
+`poll_freq`: The frequency that will be used to poll the inputs in Hz.  The default of 480 Hz will poll each sensor every 2.08 ms, which is a convenient value for debounce routines discussed later and analog averaging routines that sample across an exact number of 60 Hz cycles.
+
+**Manager.values**()
+
+This returns a snapshot of all of the current inputs.  The return object is a Python dictionary with added feature of being able to use an attribute to access a value as well as standard dictionary syntax.  If `vals` is the object returned by this method, these two read access means are equivalent:  `vals['X1']` and `vals.X1`.

inputs.py

@@ -18,7 +18,9 @@ def __init__(self, inputs, timer_num=1, poll_freq=480):
         '''Arguments are:
         inputs: a list or tuple of Inputs objects that derive from InputBase.
         time_num: the number of the microcontroller Timer that will be used to
-            periodically poll the inputs.
+            periodically poll the inputs.  If None is passed, no Timer will be
+            set up automatically and you will need to periodically call 
+            the 'service_inputs()` method from your own timer.
         poll_freq: the frequency in Hz to read the inputs.  The default value
             of 480 Hz means each input will be read every 2.08 ms (1000 ms / 480).
             Be careful about setting this too high as the time required to read
@@ -28,8 +30,9 @@ def __init__(self, inputs, timer_num=1, poll_freq=480):
             the process of reading inputs consumes 1.6 / 2.08 or 77% of the CPU cycles.
         '''
         self.inputs = inputs
-        self._tim = pyb.Timer(timer_num, freq=poll_freq)
-        self._tim.callback(self.service_inputs)
+        if timer_num is not None:
+            self._tim = pyb.Timer(timer_num, freq=poll_freq)
+            self._tim.callback(self.service_inputs)
 
     def service_inputs(self, t):
         '''This method is called by the timer interrupt and runs the 'service_input'