pwm: Rephrase edge and period detection, eliminate internal state

With the simplicity of PWM waveforms and the convenience of the v3 API,
there is no need to maintain internal state. After the start of the
first period was determined based on the input signal's polarity, any
period is defined by just the next two edges, and the next period is
immediately to follow.

1 files changed, 14 insertions, 19 deletions

diff --git a/decoders/pwm/pd.py b/decoders/pwm/pd.py
index 5d0b4a5..a2fbb0f 100644
--- a/decoders/pwm/pd.py
+++ b/decoders/pwm/pd.py
@@ -61,7 +61,6 @@ class Decoder(srd.Decoder):
             self.samplerate = value
 
     def start(self):
-        self.startedge = 0 if self.options['polarity'] == 'active-low' else 1
         self.out_ann = self.register(srd.OUTPUT_ANN)
         self.out_binary = self.register(srd.OUTPUT_BINARY)
         self.out_average = \
@@ -93,33 +92,29 @@ class Decoder(srd.Decoder):
 
     def decode(self):
 
-        # Wait for an "active" edge (depends on config).
-        self.wait({0: 'f' if self.startedge == 0 else 'r'})
+        # Wait for an "active" edge (depends on config). This starts
+        # the first full period of the inspected signal waveform.
+        self.wait({0: 'f' if self.options['polarity'] == 'active-low' else 'r'})
         self.first_samplenum = self.samplenum
-        self.start_samplenum = self.samplenum
 
-        # Handle all next edges.
+        # Keep getting samples for the period's middle and terminal edges.
+        # At the same time that last sample starts the next period.
         while True:
-            pin, = self.wait({0: 'e'})
 
-            if pin != self.startedge:
-                # Non-active edge
-                self.end_samplenum = self.ss_block = self.samplenum
-                continue
+            # Get the next two edges. Setup some variables that get
+            # referenced in the calculation and in put() routines.
+            self.start_samplenum = self.samplenum
+            pins = self.wait({0: 'e'})
+            self.end_samplenum = self.samplenum
+            pins = self.wait({0: 'e'})
+            self.ss_block = self.start_samplenum
+            self.es_block = self.samplenum
 
-            # Active edge
-            # We are on a full cycle we can calculate
-            # the period, the duty cycle and its ratio.
+            # Calculate the period, the duty cycle, and its ratio.
             period = self.samplenum - self.start_samplenum
             duty = self.end_samplenum - self.start_samplenum
             ratio = float(duty / period)
 
-            # This interval starts at this edge.
-            self.ss_block = self.start_samplenum
-            # Store the new rising edge position and the ending
-            # edge interval.
-            self.start_samplenum = self.es_block = self.samplenum
-
             # Report the duty cycle in percent.
             percent = float(ratio * 100)
             self.putx([0, ['%f%%' % percent]])