Added rollover to Counter.

Author: alanmitchell

inputs.py

@@ -210,12 +210,14 @@ class Counter(DigitalBase):
  ONE_EDGE = 1
  BOTH_EDGES = 2
 
- def __init__(self, pin_name, stable_read_count=4, edges=ONE_EDGE, reset_on_read=False, **kwargs):
+ def __init__(self, pin_name, stable_read_count=4, edges=ONE_EDGE, reset_on_read=False, 
+ rollover=2**32, **kwargs):
  '''Arguments not in the inheritance chain:
  edges: Either ONE_EDGE or BOTH_EDGES indicating which transitions of the pulse to 
  count.
  reset_on_read: if True, the counter value will be reset to 0 after the count
  is read via a call to the value() method.
+ rollover: count will roll to 0 when it hits this value.
  Note that the default 'stable_read_count' value is set to 4 reads. With the 
  default 2.1 ms read interval, this requires stability for 8.4 ms. Counters are
  often reed switches or electronic pulse trains, both of which have little to no
@@ -225,10 +227,15 @@ def __init__(self, pin_name, stable_read_count=4, edges=ONE_EDGE, reset_on_read=
  DigitalBase.__init__(self, pin_name, stable_read_count=stable_read_count, **kwargs)
  self.edges = edges
  self.reset_on_read = reset_on_read
- self._low_to_high_count = 0
- self._high_to_low_count = 0
+ self._rollover = rollover
+ self._count = 0
  self._new_val = None # need to allocate memory here, not in interrupt routine
 
+ def incr_counter(self):
+ '''Increments the count accounting for rollover.
+ '''
+ self._count = (self._count + 1) % self._rollover
+
  def service_input(self):
  # shift the prior readings over one bit, and put the new reading
  # in the LSb position.
@@ -241,29 +248,28 @@ def service_input(self):
  if self._new_val == self._cur_val:
  # no change in value
  return
- if self._new_val > self._cur_val:
- # transition from low to high occurred.
- self._low_to_high_count += 1
- else:
- # transition from high to low occurred.
- self._high_to_low_count += 1
+ if self._new_val < self._cur_val:
+ # transition from high to low occurred. Always count these
+ # transitions.
+ self.incr_counter()
+ elif self.edges == Counter.BOTH_EDGES:
+ # A low to high transition occurred and counting both edges
+ # was requested, so increment counter.
+ self.incr_counter()
  self._cur_val = self._new_val
 
  def _compute_value(self):
- if self.edges == Counter.ONE_EDGE:
- ct = self._high_to_low_count
- else:
- ct = self._high_to_low_count + self._low_to_high_count
+ ct = self._count
  if self.reset_on_read:
- self._high_to_low_count = self._low_to_high_count = 0
+ self._count = 0
  return ct
 
  def reset_count(self):
  '''Resets the counts and protects the processs form being
  interrupted.
  '''
  irq_state = pyb.disable_irq()
- self._high_to_low_count = self._low_to_high_count = 0
+ self._count = 0
  pyb.enable_irq(irq_state)