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diff --git a/decoders/transitioncounter/pd.py b/decoders/transitioncounter/pd.py
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+##
+## This file is part of the sigrok project.
+##
+## Copyright (C) 2010 Uwe Hermann <uwe@hermann-uwe.de>
+##
+## 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
+## the Free Software Foundation; either version 2 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; if not, write to the Free Software
+## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+##
+
+# Transition counter protocol decoder
+
+import sigrokdecode as srd
+
+class Decoder(srd.Decoder):
+    api_version = 1
+    id = 'transitioncounter'
+    name = 'Transition counter'
+    longname = 'Pin transition counter'
+    desc = 'Counts rising/falling edges in the signal.'
+    license = 'gplv2+'
+    inputs = ['logic']
+    outputs = ['transitioncounts']
+    probes = []
+    optional_probes = []
+    options = {}
+    annotations = [
+        ['TODO', 'TODO'],
+    ]
+
+    def __init__(self, **kwargs):
+        self.channels = -1
+        self.lastsample = None
+
+    def start(self, metadata):
+        # self.out_proto = self.add(srd.OUTPUT_PROTO, 'transitioncounter')
+        self.out_ann = self.add(srd.OUTPUT_ANN, 'transitioncounter')
+
+    def report(self):
+        pass
+
+    def decode(self, ss, es, data):
+
+        for (samplenum, s) in data:
+
+            # ...
+            if self.channels == -1:
+                self.channels = len(s)
+                self.oldbit = [0] * self.channels
+                self.transitions = [0] * self.channels
+                self.rising = [0] * self.channels
+                self.falling = [0] * self.channels
+
+            # Optimization: Skip identical samples (no transitions).
+            if self.lastsample == s:
+                continue
+
+            # Upon the first sample, store the initial values.
+            if self.lastsample == None:
+                self.lastsample = s
+                for i in range(self.channels):
+                    self.oldbit[i] = self.lastsample[i]
+
+            # Iterate over all channels/probes in this sample.
+            # Count rising and falling edges for each channel.
+            for i in range(self.channels):
+                curbit = s[i]
+                # Optimization: Skip identical bits (no transitions).
+                if self.oldbit[i] == curbit:
+                    continue
+                elif (self.oldbit[i] == 0 and curbit == 1):
+                    self.rising[i] += 1
+                elif (self.oldbit[i] == 1 and curbit == 0):
+                    self.falling[i] += 1
+                self.oldbit[i] = curbit
+
+            # Save the current sample as 'lastsample' for the next round.
+            self.lastsample = s
+
+        # Total number of transitions = rising + falling edges.
+        for i in range(self.channels):
+            self.transitions[i] = self.rising[i] + self.falling[i]
+
+        # TODO: Which output format?
+        # TODO: How to only output something after the last chunk of data?
+        outdata = []
+        for i in range(self.channels):
+            outdata.append([self.transitions[i], self.rising[i],
+                            self.falling[i]])
+
+        if outdata != []:
+            # self.put(0, 0, self.out_proto, out_proto)
+            self.put(0, 0, self.out_ann, [0, [str(outdata)]])
+