signal.lsb

cantools · Jun 29, 2021 · dd7137a · dd7137a
1 parent 24a2fea
commit dd7137a
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diff --git a/cantools/database/can/signal.py b/cantools/database/can/signal.py
@@ -174,8 +174,10 @@ def name(self, value):
 
     @property
     def start(self):
-        """The start bit position of the signal within its message.
+        """The start bit position of the signal within its message as it is saved in the dbc file.
 
+        lsb in case of little_endian,
+        msb in case of big_endian.
         """
 
         return self._start
@@ -184,6 +186,27 @@ def start(self):
     def start(self, value):
         self._start = value
 
+    @property
+    def lsb(self):
+        """The Startbit as displayed in Vector CANdb++.
+
+        The position of the least significant bit of this signal.
+        This is equivalent to start iff byte_order == little_endian.
+        """
+
+        if self.byte_order == 'big_endian':
+            i = self.start
+            for j in range(self.length-1):
+                if i % 8 == 0:
+                    i += 16
+                i -= 1
+            return i
+        elif self.byte_order == 'little_endian':
+            return self.start
+        else:
+            raise ValueError("invalid value for byte_order: %s" % self.byte_order)
+
+
     @property
     def length(self):
         """The length of the signal in bits.

diff --git a/tests/test_database.py b/tests/test_database.py
@@ -4638,6 +4638,115 @@ def test_bus_comment(self):
         self.assert_dbc_dump(db, filename)
 
 
+    def test_lsb(self):
+        filename = 'tests/files/dbc/signed.dbc'
+        db = cantools.database.load_file(filename)
+        msg = db.get_message_by_name('Message378910')
+        msg_sigs = (
+            (
+                'Message378910',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s7',      1,  7),
+                    ('s8big',   9,  8),
+                    ('s9',     17,  9),
+                    ('s8',     26,  8),
+                    ('s3',     34,  3),
+                    ('s3big',  37,  3),
+                    ('s7big',  56,  7),
+                    ('s10big', 63, 10),
+                )
+            ),
+            (
+                'Message64',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s64',     0, 64),
+                )
+            ),
+            (
+                'Message64big',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s64big', 56, 64),
+                )
+            ),
+            (
+                'Message63',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s63',     0, 63),
+                )
+            ),
+            (
+                'Message63big',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s63big', 57, 63),
+                )
+            ),
+            (
+                'Message63_1',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s63',     1, 63),
+                )
+            ),
+            (
+                'Message63big_1',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s63big', 56, 63),
+                )
+            ),
+            (
+                'Message33',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s33',     0, 33),
+                )
+            ),
+            (
+                'Message33big',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s33big', 39, 33),
+                )
+            ),
+            (
+                'Message32',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s32',     0, 32),
+                )
+            ),
+            (
+                'Message32big',
+                (
+                    # data as displayed in CANdb++ Editor
+                    # Name, Startbit, Length
+                    ('s32big', 24, 32),
+                )
+            ),
+        )
+        for msg, signal_lsb_len in msg_sigs:
+            msg = db.get_message_by_name(msg)
+            for sig, expected_lsb, length in signal_lsb_len:
+                sig = msg.get_signal_by_name(sig)
+                self.assertEqual(sig.length, length)
+                self.assertEqual(sig.lsb, expected_lsb, f'{msg.name}.{sig.name} wrong value for lsb')
+
+
 # This file is not '__main__' when executed via 'python setup.py3
 # test'.
 logging.basicConfig(level=logging.DEBUG)