Playing a bit with SocketCan and its utilities

This time I had a better look at the SocketCan utilities that I mentioned in a previous post. As I have already told, you can get and install them with these commands:

svn checkout http://svn.berlios.de/svnroot/repos/socketcan/trunk canbus
cd canbus/can-utils/
make
make install

And you will end up with lots of new programs under /usr/local/bin:

asc2log canbusload candump cangen
canlogserver canplayer cansend cansniffer
isotpdump isotprecv isotpsend isotpsniffer
isotptun log2long slcand slcanpty vcan

To see how canbus works, I tried to setup a virtual can bus with these commands:

modprobe vcan can-raw
ip link add dev vcan-test type vcan
ifconfig vcan-test up

These basically creates a canbus named vcan-test and set the interface up.
Then I opened two terminals and ran the command candump on one terminal and the command cansend on the other terminal. These are the outputs:

# cansend vcan-test 5A1#11.2233.44556677.88
# cansend vcan-test 5A1#11.2233.44556677
# cansend vcan-test 1F334455#1122334455667788

# candump vcan-test
vcan-test 5A1 [8] 11 22 33 44 55 66 77 88
vcan-test 5A1 [7] 11 22 33 44 55 66 77
vcan-test 1F334455 [8] 11 22 33 44 55 66 77 88

That are the message id and the data. The number between the brackets is the data length and the last case is with an extended id.

This could also be the text format used by the slcan driver to communicate via serial port.

I have tried to use slcanpty to attach the vcan-test interface to a pseudo terminal but without success so far. I will have to try again soon as it could be the way to gather the data on the Linux machine without writing an additional custom layer.

Canbus programming under linux: SocketCAN

Well the good news is that someone already did the hard part for us!
The Linux kernel includes since several versions the support to the can protocol and provides what seems to be a very easy interface to it. It's called SocketCAN and it is modeled after the standard unix socket API.
The project page is at BerliOS and hosts the kernel patches (not needed anymore as it is included in mainstream) and some user space tools that I just downloaded and installed without a glitch. You can get them by accessing the project subversion repository with this command: svn checkout http://svn.berlios.de/svnroot/repos/socketcan/trunk canbus

More info on what is and how to use SocketCan can be found in the linux kernel documentation directory (available on the web here)

As for the device drivers, SocketCAN supports a few drivers alreay, two of which are particularly interesting: vcan and slcan. Vcan is a virtual CAN interface driver and is there for testing when there is no hardware available. This will be probably the first to try once I realize how the user space utilities work. The slcan driver is "For a bunch of CAN adaptors that are attached via a serial line ASCII protocol (for serial / USB adaptors)" and should match exactly what we are trying to do. I just wonder what is the data format the slcan drivers expects to receive from the serial port. I have only found a strange document here so far but the semantic is not clear to me and I will have to investigate this further.