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About

CAN BUS tools in Python 3.

  • DBC, KCD, SYM, ARXML 3&4 and CDD file parsing.
  • CAN message encoding and decoding.
  • Simple and extended signal multiplexing.
  • Diagnostic DID encoding and decoding.
  • candump output decoder.
  • Node tester.
  • C source code generator.
  • CAN bus monitor.
  • Graphical plots of signals.

Project homepage: https://github.com/eerimoq/cantools

Documentation: https://cantools.readthedocs.io

Installation

python3 -m pip install cantools

Example usage

Scripting

The example starts by parsing a small DBC-file and printing its messages and signals.

>>> import cantools
>>> from pprint import pprint
>>> db = cantools.database.load_file('tests/files/dbc/motohawk.dbc')
>>> db.messages
[message('ExampleMessage', 0x1f0, False, 8, 'Example message used as template in MotoHawk models.')]
>>> example_message = db.get_message_by_name('ExampleMessage')
>>> pprint(example_message.signals)
[signal('Enable', 7, 1, 'big_endian', False, 1.0, 0, 0.0, 0.0, '-', False, None, {0: 'Disabled', 1: 'Enabled'}, None),
 signal('AverageRadius', 6, 6, 'big_endian', False, 0.1, 0, 0.0, 5.0, 'm', False, None, None, ''),
 signal('Temperature', 0, 12, 'big_endian', True, 0.01, 250, 229.53, 270.47, 'degK', False, None, None, None)]

The example continues encoding a message and sending it on a CAN bus using the python-can package.

>>> import can
>>> can_bus = can.interface.Bus('vcan0', bustype='socketcan')
>>> data = example_message.encode({'Temperature': 250.1, 'AverageRadius': 3.2, 'Enable': 1})
>>> message = can.Message(arbitration_id=example_message.frame_id, data=data)
>>> can_bus.send(message)

Alternatively, a message can be encoded using the encode_message() method on the database object.

The last part of the example receives and decodes a CAN message.

>>> message = can_bus.recv()
>>> db.decode_message(message.arbitration_id, message.data)
{'AverageRadius': 3.2, 'Enable': 'Enabled', 'Temperature': 250.09}

See examples for additional examples.

Command line tool

The decode subcommand

Decode CAN frames captured with the Linux program candump.

$ candump vcan0 | python3 -m cantools decode tests/files/dbc/motohawk.dbc
  vcan0  1F0   [8]  80 4A 0F 00 00 00 00 00 ::
ExampleMessage(
    Enable: 'Enabled' -,
    AverageRadius: 0.0 m,
    Temperature: 255.92 degK
)
  vcan0  1F0   [8]  80 4A 0F 00 00 00 00 00 ::
ExampleMessage(
    Enable: 'Enabled' -,
    AverageRadius: 0.0 m,
    Temperature: 255.92 degK
)
  vcan0  1F0   [8]  80 4A 0F 00 00 00 00 00 ::
ExampleMessage(
    Enable: 'Enabled' -,
    AverageRadius: 0.0 m,
    Temperature: 255.92 degK
)

Alternatively, the decoded message can be printed on a single line:

$ candump vcan0 | python3 -m cantools decode --single-line tests/files/dbc/motohawk.dbc
  vcan0  1F0   [8]  80 4A 0F 00 00 00 00 00 :: ExampleMessage(Enable: 'Enabled' -, AverageRadius: 0.0 m, Temperature: 255.92 degK)
  vcan0  1F0   [8]  80 4A 0F 00 00 00 00 00 :: ExampleMessage(Enable: 'Enabled' -, AverageRadius: 0.0 m, Temperature: 255.92 degK)
  vcan0  1F0   [8]  80 4A 0F 00 00 00 00 00 :: ExampleMessage(Enable: 'Enabled' -, AverageRadius: 0.0 m, Temperature: 255.92 degK)

The plot subcommand

The plot subcommand is similar to the decode subcommand but messages are visualized using matplotlib instead of being printed to stdout.

$ candump -l vcan0
$ cat candump-2021-01-04_180521.log
(1609779922.655421) vcan0 00000343#B204B9049C049C04
(1609779922.655735) vcan0 0000024A#120527052E051905
(1609779923.657524) vcan0 00000343#C404C404CB04C404
(1609779923.658086) vcan0 0000024A#8B058B058B059205
(1609779924.659912) vcan0 00000343#5C04790479045504
(1609779924.660471) vcan0 0000024A#44064B0659064406
(1609779925.662277) vcan0 00000343#15040704F203F203
(1609779925.662837) vcan0 0000024A#8B069906A706A706
(1609779926.664191) vcan0 00000343#BC03B503A703BC03
(1609779926.664751) vcan0 0000024A#A006A706C406C406

$ cat candump-2021-01-04_180521.log | python3 -m cantools plot tests/files/dbc/abs.dbc

docs/plot-1.png

If you don't want to show all signals you can select the desired signals with command line arguments. A * can stand for any number of any character, a ? for exactly one arbitrary character. Signals separated by a - are displayed in separate subplots. Optionally a format can be specified after a signal, separated by a colon.

$ cat candump-2021-01-04_180521.log | python3 -m cantools plot tests/files/dbc/abs.dbc '*33.*fl:-<' '*33.*fr:->' - '*33.*rl:-<' '*33.*rr:->'

docs/plot-2-subplots.png

Signals with a different range of values can be displayed in the same subplot on different vertical axes by separating them with a comma.

$ cat candump-2021-01-04_180521.log | cantools plot --auto-color tests/files/dbc/abs.dbc -- \
   --ylabel 'Bremse 33' '*_33.*fl*:-<' '*_33.*fr*:>' '*_33.*rl*:3' '*_33.*rr*:4' , \
   --ylabel 'Bremse 2' '*_2.*fl*:-<' '*_2.*fr*:>' '*_2.*rl*:3' '*_2.*rr*:4'

docs/plot-2-axes.png

Matplotlib comes with different preinstalled styles that you can use:

$ cat candump-2021-01-04_180521.log | cantools plot tests/files/dbc/abs.dbc --style seaborn

docs/plot-seaborn.png

You can try all available styles with

$ cantools plot --list-styles . | sed -n '/^- /s/^- //p' | while IFS= read -r style; do
      cat candump-2021-01-04_180521.log | cantools plot tests/files/dbc/abs.dbc --style "$style" --title "--style '$style'"
  done

For more information see

$ python3 -m cantools plot --help

Note that by default matplotlib is not installed with cantools. But it can be by specifying an extra at installation:

$ python3 -m pip install cantools[plot]

The dump subcommand

Dump given database in a human readable format:

$ python3 -m cantools dump tests/files/dbc/motohawk.dbc
================================= Messages =================================

  ------------------------------------------------------------------------

  Name:       ExampleMessage
  Id:         0x1f0
  Length:     8 bytes
  Cycle time: - ms
  Senders:    PCM1
  Layout:

                          Bit

             7   6   5   4   3   2   1   0
           +---+---+---+---+---+---+---+---+
         0 |<-x|<---------------------x|<--|
           +---+---+---+---+---+---+---+---+
             |                       +-- AverageRadius
             +-- Enable
           +---+---+---+---+---+---+---+---+
         1 |-------------------------------|
           +---+---+---+---+---+---+---+---+
         2 |----------x|   |   |   |   |   |
     B     +---+---+---+---+---+---+---+---+
     y               +-- Temperature
     t     +---+---+---+---+---+---+---+---+
     e   3 |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+
         4 |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+
         5 |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+
         6 |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+
         7 |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+

  Signal tree:

    -- {root}
       +-- Enable
       +-- AverageRadius
       +-- Temperature

  Signal choices:

    Enable
        0 Disabled
        1 Enabled

  ------------------------------------------------------------------------

The list subcommand

Print all information of a given database in a human readable format. This is very similar to the "dump" subcommand, but the output is less pretty, slightly more comprehensive and easier to parse by shell scripts:

$ python3 -m cantools list -a tests/files/dbc/motohawk.dbc
ExampleMessage:
  Comment[None]: Example message used as template in MotoHawk models.
  Frame ID: 0x1f0 (496)
  Size: 8 bytes
  Is extended frame: False
  Signals:
    Enable:
      Type: Integer
      Start bit: 7
      Length: 1 bits
      Unit: -
      Is signed: False
      Named values:
        0: Disabled

The generate C source subcommand

Generate C source code from given database.

The generated code contains:

Known limitations:

  • The maximum signal size is 64 bits, which in practice is never exceeded.

Below is an example of how to generate C source code from a database. The database is tests/files/dbc/motohawk.dbc.

$ python3 -m cantools generate_c_source tests/files/dbc/motohawk.dbc
Successfully generated motohawk.h and motohawk.c.

See motohawk.h and motohawk.c for the contents of the generated files.

In this example we use --use-float so floating point numbers in the generated code are single precision (float) instead of double precision (double).

$ python3 -m cantools generate_c_source --use-float tests/files/dbc/motohawk.dbc
Successfully generated motohawk.h and motohawk.c.

In the next example we use --database-name to set a custom namespace for all generated types, defines and functions. The output file names are also changed by this option.

$ python3 -m cantools generate_c_source --database-name my_database_name tests/files/dbc/motohawk.dbc
Successfully generated my_database_name.h and my_database_name.c.

See my_database_name.h and my_database_name.c for the contents of the generated files.

In the next example we use --no-floating-point-numbers to generate code without floating point types, i.e. float and double.

$ python3 -m cantools generate_c_source --no-floating-point-numbers tests/files/dbc/motohawk.dbc
Successfully generated motohawk.h and motohawk.c.

See motohawk_no_floating_point_numbers.h and motohawk_no_floating_point_numbers.c for the contents of the generated files.

In the last example --node is used to generate message pack functions only for messages sent by the specified node and unpack functions only for messages with its signal receivers belonging to that node.

$ cantools generate_c_source tests/files/dbc/motohawk.dbc --node PCM1
Successfully generated motohawk.h and motohawk.c.

See motohawk_sender_node.h and motohawk_sender_node.c for the contents of the generated files.

Other C code generators:

The monitor subcommand

Monitor CAN bus traffic in a text based user interface.

$ python3 -m cantools monitor tests/files/dbc/motohawk.dbc

https://github.com/eerimoq/cantools/raw/master/docs/monitor.png

The menu at the bottom of the monitor shows the available commands.

  • Quit: Quit the monitor. Ctrl-C can be used as well.
  • Filter: Only display messages matching given regular expression. Press <Enter> to return to the menu from the filter input line.
  • Play/Pause: Toggle between playing and paused (or running and freezed).
  • Reset: Reset the monitor to its initial state.

Contributing

  1. Fork the repository.

  2. Install prerequisites.

    python3 -m pip install -r requirements.txt
    
  3. Implement the new feature or bug fix.

  4. Implement test case(s) to ensure that future changes do not break legacy.

  5. Run the tests.

    make test
    
  6. Create a pull request.