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SocketCAN

The SocketCAN documentation can be found in the Linux kernel docs in the networking directory. Quoting from the SocketCAN Linux documentation:

The socketcan package is an implementation of CAN protocols (Controller Area Network) for Linux. CAN is a networking technology which has widespread use in automation, embedded devices, and automotive fields. While there have been other CAN implementations for Linux based on character devices, SocketCAN uses the Berkeley socket API, the Linux network stack and implements the CAN device drivers as network interfaces. The CAN socket API has been designed as similar as possible to the TCP/IP protocols to allow programmers, familiar with network programming, to easily learn how to use CAN sockets.

Important

python-can versions before 2.2 had two different implementations named socketcan_ctypes and socketcan_native. These were removed in version 4.0.0 after a deprecation period.

Socketcan Quickstart

The CAN network driver provides a generic interface to setup, configure and monitor CAN devices. To configure bit-timing parameters use the program ip.

The virtual CAN driver (vcan)

The virtual CAN interfaces allow the transmission and reception of CAN frames without real CAN controller hardware. Virtual CAN network devices are usually named 'vcanX', like vcan0 vcan1 vcan2.

To create a virtual can interface using socketcan run the following:

sudo modprobe vcan
# Create a vcan network interface with a specific name
sudo ip link add dev vcan0 type vcan
sudo ip link set vcan0 up

Real Device

vcan should be substituted for can and vcan0 should be substituted for can0 if you are using real hardware. Setting the bitrate can also be done at the same time, for example to enable an existing can0 interface with a bitrate of 1MB:

sudo ip link set can0 up type can bitrate 1000000

CAN over Serial / SLCAN

SLCAN adapters can be used directly via :doc:`/interfaces/slcan`, or via :doc:`/interfaces/socketcan` with some help from the slcand utility which can be found in the can-utils package.

To create a socketcan interface for an SLCAN adapter run the following:

slcand -f -o -c -s5 /dev/ttyAMA0
ip link set up slcan0

Names of the interfaces created by slcand match the slcan\d+ regex. If a custom name is required, it can be specified as the last argument. E.g.:

slcand -f -o -c -s5 /dev/ttyAMA0 can0
ip link set up can0

PCAN

Kernels >= 3.4 supports the PCAN adapters natively via :doc:`/interfaces/socketcan`, so there is no need to install any drivers. The CAN interface can be brought like so:

sudo modprobe peak_usb
sudo modprobe peak_pci
sudo ip link set can0 up type can bitrate 500000

Intrepid

The Intrepid Control Systems, Inc provides several devices (e.g. ValueCAN) as well as Linux module and user-space daemon to make it possible to use them via SocketCAN.

Refer to below repositories for installation instructions:

Send Test Message

The can-utils library for Linux includes a cansend tool which is useful to send known payloads. For example to send a message on vcan0:

cansend vcan0 123#DEADBEEF

CAN Errors

A device may enter the "bus-off" state if too many errors occurred on the CAN bus. Then no more messages are received or sent. An automatic bus-off recovery can be enabled by setting the "restart-ms" to a non-zero value, e.g.:

sudo ip link set canX type can restart-ms 100

Alternatively, the application may realize the "bus-off" condition by monitoring CAN error frames and do a restart when appropriate with the command:

ip link set canX type can restart

Note that a restart will also create a CAN error frame.

List network interfaces

To reveal the newly created can0 or a vcan0 interface:

ifconfig

Display CAN statistics

ip -details -statistics link show vcan0

Network Interface Removal

To remove the network interface:

sudo ip link del vcan0

Wireshark

Wireshark supports socketcan and can be used to debug python-can messages. Fire it up and watch your new interface.

To spam a bus:

import time
import can

interface = 'socketcan'
channel = 'vcan0'

def producer(id):
    """:param id: Spam the bus with messages including the data id."""
    bus = can.Bus(channel=channel, interface=interface)
    for i in range(10):
        msg = can.Message(arbitration_id=0xc0ffee, data=[id, i, 0, 1, 3, 1, 4, 1], is_extended_id=False)
        bus.send(msg)

    time.sleep(1)

producer(10)

With debugging turned right up this looks something like this:

../images/wireshark.png

The process to follow bus traffic is even easier:

for message in Bus(can_interface):
    print(message)

Reading and Timeouts

Reading a single CAN message off of the bus is simple with the bus.recv() function:

import can

bus = can.Bus(channel='vcan0', interface='socketcan')
message = bus.recv()

By default, this performs a blocking read, which means bus.recv() won't return until a CAN message shows up on the socket. You can optionally perform a blocking read with a timeout like this:

message = bus.recv(1.0)  # Timeout in seconds.

if message is None:
    print('Timeout occurred, no message.')

If you set the timeout to 0.0, the read will be executed as non-blocking, which means bus.recv(0.0) will return immediately, either with a Message object or None, depending on whether data was available on the socket.

Filtering

The implementation features efficient filtering of can_id's. That filtering occurs in the kernel and is much much more efficient than filtering messages in Python.

Broadcast Manager

The socketcan interface implements thin wrappers to the linux broadcast manager socket api. This allows the cyclic transmission of CAN messages at given intervals. The overhead for periodic message sending is extremely low as all the heavy lifting occurs within the linux kernel.

The :class:`~can.BusABC` initialized for socketcan interface transparently handles scheduling of CAN messages to Linux BCM via :meth:`~can.BusABC.send_periodic`:

with can.interface.Bus(interface="socketcan", channel="can0") as bus:
    task = bus.send_periodic(...)

More examples that uses :meth:`~can.BusABC.send_periodic` are included in python-can/examples/cyclic.py.

The task object returned by :meth:`~can.BusABC.send_periodic` can be used to halt, alter or cancel the periodic message task:

.. autoclass:: can.interfaces.socketcan.CyclicSendTask
    :members:

Buffer Sizes

Currently, the sending buffer size cannot be adjusted by this library. However, this issue describes how to change it via the command line/shell.

Bus

The :class:`~can.interfaces.socketcan.SocketcanBus` specializes :class:`~can.BusABC` to ensure usage of SocketCAN Linux API. The most important differences are:

  • usage of SocketCAN BCM for periodic messages scheduling;
  • filtering of CAN messages on Linux kernel level;
  • usage of nanosecond timings from the kernel.
.. autoclass:: can.interfaces.socketcan.SocketcanBus
    :members:
    :inherited-members: