1 files changed, 74 insertions, 0 deletions
diff --git a/decoders/ddc.py b/decoders/ddc.py
new file mode 100644
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+++ b/decoders/ddc.py
@@ -0,0 +1,74 @@
+##
+## This file is part of the sigrok project.
+##
+## Copyright (C) 2012 Bert Vermeulen <bert@biot.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
+## the Free Software Foundation; either version 3 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, If not, see <http://www.gnu.org/licenses/>.
+##
+
+#
+# DDC protocol decoder
+#
+# This decoder extracts a DDC stream from an I2C session between a computer
+# and a display device. The stream is output as plain bytes.
+#
+
+import sigrokdecode
+
+
+class Decoder(sigrokdecode.Decoder):
+    id = 'ddc'
+    name = 'DDC'
+    longname = 'Display Data Channel'
+    desc = 'DDC is a protocol for communication between computers and displays.'
+    longdesc = ''
+    author = 'Bert Vermeulen <bert@biot.com>'
+    license = 'gplv3+'
+    inputs = ['i2c']
+    outputs = ['ddc']
+    annotation = [
+        ["Byte stream", "DDC byte stream as read from display."],
+    ]
+
+    def __init__(self, **kwargs):
+        self.state = None
+
+    def start(self, metadata):
+        self.output_annotation = self.add(sigrokdecode.SRD_OUTPUT_ANNOTATION, 'ddc')
+
+    def decode(self, start_sample, end_sample, i2c_data):
+        try:
+            cmd, data, ack_bit = i2c_data
+        except Exception as e:
+            raise Exception("malformed I2C input: %s" % str(e)) from e
+
+        if self.state is None:
+            # waiting for the DDC session to start
+            if cmd in ('START', 'START_REPEAT'):
+                self.state = 'start'
+        elif self.state == 'start':
+            if cmd == 'ADDRESS_READ' and data == 80:
+                # 80 is the I2C slave address of a connected display,
+                # so this marks the start of the DDC data transfer.
+                self.state = 'transfer'
+            elif cmd == 'STOP':
+                # back to idle
+                self.state = None
+        elif self.state == 'transfer':
+            if cmd == 'DATA_READ':
+                # there shouldn't be anything but data reads on this
+                # address, so ignore everything else
+                self.put(start_sample, end_sample, self.output_annotation,
+                         [0, ["0x%.2x" % data]])
+