pwm: Fix and rework

Reworked in the algorithm:
 - Fixed the polarity setting
 - Taken in consideration the first transition
 - Using the 'None' state instead of -1 and 0 value
 - Simplify the algorithm and remove useless branches and variables
 - Avoid re-calculating the same thing more than once
 - Renamed a few variables for a better understanding
 - Duty cycle precision changed to floating value

Otherwise:
 - Added a meta OUTPUT for the duty cycle average
 - Renamed the polarity option:
	'polarity', 'active low/high' are well-understood terms.
 - Added comments

Signed-off-by: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>

1 files changed, 56 insertions, 33 deletions

diff --git a/decoders/pwm/pd.py b/decoders/pwm/pd.py
index 999b496..148b34b 100644
--- a/decoders/pwm/pd.py
+++ b/decoders/pwm/pd.py
@@ -2,6 +2,7 @@
 ## This file is part of the libsigrokdecode project.
 ##
 ## Copyright (C) 2014 Torsten Duwe <duwe@suse.de>
+## Copyright (C) 2014 Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
 ##
 ## This program is free software; you can redistribute it and/or modify
 ## it under the terms of the GNU General Public License as published by
@@ -30,68 +31,90 @@ class Decoder(srd.Decoder):
     inputs = ['logic']
     outputs = ['pwm']
     channels = (
-        {'id': 'pwm', 'name': 'PWM in', 'desc': 'Modulation pulses'},
+        {'id': 'data', 'name': 'Data', 'desc': 'Data line'},
     )
     options = (
-        {'id': 'new_cycle_edge', 'desc': 'New cycle on which edge',
-            'default': 'rising', 'values': ('rising', 'falling')},
+        {'id': 'polarity', 'desc': 'Polarity', 'default': 'active-high',
+            'values': ('active-low', 'active-high')},
     )
     annotations = (
-        ('value', 'PWM value'),
+        ('duty-cycle', 'Duty cycle'),
     )
     binary = (
         ('raw', 'RAW file'),
     )
 
     def __init__(self, **kwargs):
-        self.ss = self.es = -1
-        self.high = 1
-        self.low = 1
-        self.lastedge = 0
-        self.oldpin = 0
-        self.startedge = 0
+        self.ss = self.es = None
+        self.first_transition = True
+        self.first_samplenum = None
+        self.start_samplenum = None
+        self.end_samplenum = None
+        self.oldpin = None
         self.num_cycles = 0
+        self.average = 0
 
     def start(self):
-        self.out_python = self.register(srd.OUTPUT_PYTHON)
+        self.startedge = 0 if self.options['polarity'] == 'active-low' else 1
         self.out_ann = self.register(srd.OUTPUT_ANN)
         self.out_bin = self.register(srd.OUTPUT_BINARY)
-        self.out_freq = self.register(srd.OUTPUT_META,
-            meta=(int, 'Frequency', 'PWM base (cycle) frequency'))
-        self.startedge = 0
-        if self.options['new_cycle_edge'] == 'falling':
-            self.startedge = 1
+        self.out_average = \
+            self.register(srd.OUTPUT_META,
+                          meta=(float, 'Average', 'PWM base (cycle) frequency'))
 
     def putx(self, data):
         self.put(self.ss, self.es, self.out_ann, data)
 
-    def putp(self, data):
-        self.put(self.ss, self.es, self.out_python, data)
-
     def putb(self, data):
         self.put(self.num_cycles, self.num_cycles, self.out_bin, data)
 
     def decode(self, ss, es, data):
+
         for (self.samplenum, pins) in data:
             # Ignore identical samples early on (for performance reasons).
             if self.oldpin == pins[0]:
                 continue
 
-            if self.oldpin == 0: # Rising edge.
-                self.low = self.samplenum - self.lastedge
-            else:
-                self.high = self.samplenum - self.lastedge
+            # Initialize self.oldpins with the first sample value.
+            if self.oldpin is None:
+                self.oldpin = pins[0]
+                continue
 
-            if self.oldpin == self.startedge:
-                self.es = self.samplenum # This interval ends at this edge.
-                if self.ss >= 0: # Have we completed a hi-lo sequence?
-                    self.putx([0, ["%d%%" % ((100 * self.high) // (self.high + self.low))]])
-                    self.putb((0, bytes([(256 * self.high) // (self.high + self.low)])))
-                self.num_cycles += 1
+            if self.first_transition:
+                # First rising edge
+                if self.oldpin != self.startedge:
+                    self.first_samplenum = self.samplenum
+                    self.start_samplenum = self.samplenum
+                    self.first_transition = False
             else:
-                # Mid-interval.
-                # This interval started at the previous edge.
-                self.ss = self.lastedge
+                if self.oldpin != self.startedge:
+                    # Rising edge
+                    # We are on a full cycle we can 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 = self.start_samplenum
+                    # Store the new rising edge position and the ending
+                    # edge interval.
+                    self.start_samplenum = self.es = self.samplenum
+
+                    # Report the duty cycle in percent.
+                    percent = float(ratio * 100)
+                    self.putx([0, ["%f%%" % percent]])
+
+                    # Report the duty cycle in the binary output.
+                    self.putb((0, bytes([int(ratio * 256)])))
+
+                    # Update and report the new duty cycle average.
+                    self.num_cycles += 1
+                    self.average += percent
+                    self.put(self.first_samplenum, self.es, self.out_average,
+                             float(self.average / self.num_cycles))
+                else:
+                    # Falling edge
+                    self.end_samplenum = self.ss = self.samplenum
 
-            self.lastedge = self.samplenum
             self.oldpin = pins[0]