Excansock

Excansock is an Elixir library, that allows you to communicate using CAN bus through SocketCAN API. As SocketCAN is Linux specific, this project is useful only on Linux operating system.

Example use

Start the Excansock GenServer:

iex> {:ok, pid} = Excansock.start_link
{:ok, #PID<0.132.0>}

The GenServer doesn't open a socket automatically, so you need to tell it first to do so. The CAN network interface must be initialized and up.

iex> Excansock.open(pid, "can0")
:ok

The process calling the open function is automatically registered as receiver for the CAN frames.

We can try to send some frame on the bus like so:

iex> frame = %Excansock.CanFrame{ id: 1, data: <<1, 2, 3, 4>> }
%Excansock.CanFrame{data: <<1, 2, 3, 4>>, id: 1}

iex> Excansock.send(pid, frame)
:ok

To receive frame we should either call receive or implement appropriate callback if our receiving module is gen_server

iex> receive do msg -> msg end
{:can_data_frame, %Excansock.CanFrame{data: <<1, 2, 3, 4>>, id: 1}}

C compiler dependencies

Since this library includes C code, make, gcc, and Erlang header and development libraries are required.

On Linux systems, this usually requires you to install the build-essential and erlang-dev packages. For example:

sudo apt-get install build-essential erlang-dev

ENOBUFS error

If you experience ENOBUFS error during transmission, it means txqueuelen parameter of can interface is se too low.

You can set it higher by executing:

ip link set can0 txqueuelen 100

As a rule of thumb, the txqueuelen should be set to the number of simultaneously used CAN sockets in the system multiplied by 15.

More information about this problem can be found here: SocketCAN and queueing disciplines: Final Report, chapter 3.4.

Testing

Before running tests, you need to initialize virtual can interface vcan0 (as root or using sudo)

Run in shell:

modprobe vcan
ip link add dev vcan0 type vcan
ip link set up vcan0

Than you can run:

mix test

For some tests you need real can bus and another device, which electively echoes received messages without reordering them. To run these tests, set REAL_CAN_INTERFACE environment variable to real interface name (such as can0) and run mix test.