1. A quick look at SocketCAN
Piotr Nikiel, ATLAS Central DCS
25 Feb 2014

2. CANopen Readout Chain OPC UA Server CAN Bus File System
SocketCAN
Configurable
hardware interface
OPC UA Server
Vendor SocketCAN driver module
UNIX Sockets
CAN Hardware Interface
Vendor-specific Win64/Linux Driver
Vendor API
CANOpen
XML
OPC UA TCP/IP
XML Configuration File
File System
WinCC OA System
OPC UA Client
fwElmb
CAN Bus
WCCOA XML

3. User’s perspective You plug a SocketCAN device into a computer
Kernel loads a corresponding device driver
Standard Linux kernel has ~10 CAN device drivers (e.g. Kvaser)
ATLAS DCS provides production RPM for SysTec
CAN network interface shows up (e.g. can0)
Interface can be opened by any application e.g.
OPC UA CANopen server
Standard Linux tools: ifconfig, tcpdump, ip, …
CAN utils: candump, cansend, cangen, …

4. Operating System’s perspective
SocketCAN is a subclass of standard Network Interface, like Ethernet or Wi-Fi
So it inherits abundance of features and tools
ifconfig:
ip link set can0 type can bitrate
tcpdump can0
Queues & buffers configuration
sysfs, udev, … everything
-bash-4.1$ ifconfig
can Link encap:UNSPEC HWaddr 0E-58-F
UP RUNNING NOARP MTU:16 Metric:1

5. Programmer’s perspective
The traditional Sockets API – stable, mature, reliable and proven for 40+ years
No specific libraries, headers, frameworks needed
100% compatibility among various vendors/products
Natural richness of Unix Sockets comes at no expense:
Blocking/nonblocking calls
select(), poll(), …
Native error support (strerror(), perror(), …)
Convenience library for interface setup: libsocketcan

6. Programming example – Query State of an ELMB
Send NodeGuard request CAN frame can_frame f; f.can_id = (0x700 + elmbId) | CAN_RTR_FRAME; f.can_dlc = 0; write (sock, (void*) &f, sizeof f);
Receive CAN frame containing the ELMB’s response read (sock, (void*) &f, sizeof f); printf (“ELMB state: %u\n”, f.data[0]);

7. SysTec RPM Our branch of SysTec Driver: Has some local fixes
Has some improvements for configuration
Has nice status tools:
Is packaged in a production ready RPM
~]$ /opt/systec_can/systec_status.py
Port State | [green led] [red led] |
can0 OK(certain) |
can1 OK(certain) |
can2 BAD(UNCERTAIN) | ?blink? blink
can3 OK(certain) |
can4 BAD(UNCERTAIN) | ?blink? blink
can5 BAD(UNCERTAIN) | ?blink? blink
can6 Port closed(no info) | ?
can7 Port closed(no info) | ?