Linux CAN BUS
linux can bus is a fundemental part in embedded linux systems
used in industry. Some of the embedded linux boards has the can
module on themselve and there is no need for extra can bus adaptor
to connect to can devices. Therefore, for using canbus inside the
OS it's just needed to enbale the can feature in the kernel.
But sometimes it's very usefull to debug the software running on
an embedded linux board in a linux pc and debug or monitor the
program more easily. When the program uses the can bus of the board
we need to provide the linux can interface to the linux PC and here
canusb modules come to play their roles.
CANUSB connectors are very popular in windows world but there
are little documentations on how to use them with a linux pc or in
the other words canusb linux are not very known.
In linux the CAN protocol is supported by linux SocketCAN
library and lots of utilies are there such as can-util to do all
the things that can softwares such as can analyser, can monitor,
can logger or canbus sniffer can do.
LAWICEL CANUSB
Two types of device drivers for CAN exist in linux: Character
device based drivers and network socket based drivers.
The Linux kernel supports CAN with the SocketCAN framework. this
framework uses the model of network devices, which
allows multiple applications to access one CAN device
simultaneously. But LAWICEL CANUSB is controlled by the
ASCII protocol and is based on based on the model of
character devices.
In order to use of these type of CANUSBs like lawicel can bus
adaptor, the slcan driver provides a CAN
network device for these type of CAN
interfaces. The slcan driver converts the ASCII
frames to structcan_frame which is used in the Linux CAN
subsystem (aka SocketCAN linux). You may have a CAN device
supporting the SLCAN protocol on RS232, USB-serial adapters,
whatever.
This can bus interface named CANUSB or Lawicel CANUSB has the
following properties:
- Can handle up to 1Mbit/s CAN bitrate
- Industrial Temp range -40C to +85C
- USB 2.0 Full Speed, uses FTDI FT245RL usb chip
- Philips SJA1000 CAN Controller running at 16Mhz
- Philips 82C251 CAN Tranceiver (ISO 11898-24V)
- Compliant to CAN 2.0A (11bit ID) & CAN 2.0B (29bit ID)
- Supports RTR frames
- 32 CAN frames deep FIFO buffer for incomming frames
- Time Stamp (optional) in mS for incomming frames
- CAN connection according to CiA DS102-1 standard
- Power supplied via USB
- Free Interface DLL (32 & 64bit) or low level Ascii Commands
API
- Free Windows USB driver available (32 & 64bit)
- Free Linux USB driver available
- Free MacOS USB driver available
Prepare linux-can and CAN utils
Load kernel modules
Load the kernel modules we need for CAN. On Ubuntu these modules
are already available, so we don't need to compile it.
$ sudo modprobe can
$ sudo modprobe can-raw
$ sudo modprobe slcan
Prepare CAN utils
Get and compile the
$ git clone
https://gitorious.org/linux-can/can-utils.git
$ cd can-utils
$ make
Plug USB, Attach and startup can interface
$ sudo ./slcan_attach -f -s5 -o
/dev/ttyUSB0
attached tty /dev/ttyUSB0
to netdevice slcan0
$ sudo ./slcand ttyUSB0 slcan0
$ sudo ifconfig slcan0 up
The parameter "s5" stands
for baudrate 250k.
Now, the linux-can and the CAN utils are ready
and can be used with the usb can. Use the command line
CAN utils Linux-can and utils prepared? It's time to
use it for analysing the can module
Dump can messages from the CAN controller
Display the messages received with the CAN interface.
$ candump slcan0
Send sequences of CAN frames to CAN USB Adaptor
For some tests its very useful to send sequences. First prepare
a file with the messages:
$ cat test.log
(0.1) slcan0 5D1#0000
(0.2) slcan0 271#0100
(0.3) slcan0 289#72027000
(0.4) slcan0 401#081100000000
And now play it:
$ canplayer -l 20 -I test.log -v -g500
Other Resources:
- There is an instruction for installing the CAN driver linux on
a linux machine here.
- The ftdi usb driver linux (d2xx driver) can be found here
