can

CAN binding for Erlang

CAN or Controller Area Network for short, is a two wire serial protcol for industrial applications.

This implementation currently supports three different backends:

can_usb: CANUSB is a USB dongle from LAWICEL AB.
can_udp: This is my own invention. A simple repackaging of CAN frames into UDP/IP datagrams sent over local multicast channel.
can_sock: A binding to linux SocketCAN interface.

Any number of backend interfaces may be started and attached to the can_router, which is the main interface to receice and send CAN frames.
An application will typically call can_router:attach() and then receive CAN frames from any of the interfaces. To send a frame then simple call can:send/n, this will pass the CAN frame to all the interfaces and connected local applications in the Erlang node.

Dependencies

To build can you will need a working installation of Erlang R15B (or later).
Information on building and installing Erlang/OTP can be found here (more info).

can is built using rebar that can be found here, with building instructions here. rebar's dynamic configuration mechanism, described here, is used so the environment variable REBAR_DEPS should be set to the directory where your erlang applications are located.

can also requires the following applications to be installed:

dthread - https://github.com/tonyrog/dthread
uart - https://github.com/tonyrog/uart
can - https://github.com/Feuerlabs/lager

Downloading

Clone the repository in a suitable location:

$ git clone git://github.com/tonyrog/can.git

Configurating

Interfaces can be added and remove dynamically, but can also be initialized in the environment like:

{can, [{interfaces,
         [{can_udp, 1, []},
          {can_udp, 2, [{ttl,0}]},
      {can_usb, 1, [{device, "/dev/tty.usbserial-LWQ6UYOM"},
                        {bitrate, 125000}]},
          {can_usb, 2, [{device, "/dev/tty.usbserial-LWQ8CA1K"},
                        {bitrate, 250000}]},
          {can_sock, "can0", []},
          {can_sock, "vcan0", []}]}]}

There is a special "wakeup" frame that can be enabled by setting wakeup to true. This together with wakeup_timeout will make sure that the can bus gets a "dummy" frame sent before the real message when neccesary.

If wakeup_timeout milliseconds (15s) has passed since the interface saw some input frames or no frames where sent from that interface, then the wakeup frame is sent.

{can, [{wakeup, true},
       {wakeup_timeout, 15000},
   {interfaces,[
      {can_usb, 1, [{device, "/dev/tty.usbserial-LWQ8CA1K"},
                        {bitrate, 250000}]}
      {can_usb, 2, [{device, "/dev/tty.usbserial-LWQ6UYOM"},
                        {bitrate, 250000}]}
    ]}]}.

The wakeup frame looks like this ( maybe configure per interface ? ):

<<16#80,16#2802:16/little,0:8,1:32/little>>

And is sent to the PDO_TX1 for the current target node.

The interfaces in the environment will get under supervision.

Concepts

Linux virtual can driver

load the driver

$ sudo modprobe vcan

Create a virtual CAN network interface called 'vcan0'

$ sudo ip link add dev vcan0 type vcan

Activate a virtual CAN network interface called 'vcan0'

$ sudo ifconfig vcan0 up

Remove a (virtual) CAN network interface 'vcan0'

$ sudp ip link del vcan0

Create a virtual CAN network interface

$ sudo ip link add type vcan

...

Files

...

Building

Rebar will compile all needed dependencies.
Compile:

$ cd can
$ rebar compile
...
==> can (compile)

Running

$ erl -pa <path>/can/ebin
>can_router:start().

(Instead of specifing the path to the ebin directory you can set the environment ERL_LIBS.)

Stop:

>halt().

b / can

can