How to configure and use CAN bus

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This article explains how to enable the CAN bus using as examples the AM35x EVM and [[:Category:OMAP35x OMAP35x], but can be applied to other platforms as well. In addition, steps to exchange data with a MCP2515 Bus Monitor board is also documented.

Contents

Enable the CAN controller kernel driver

AM35x kernel

In the case of the Category:AM35x platform the configuration is:

Linux Kernel Configuration
     Networking support
        CAN bus subsystem support
           CAN device drivers
               Platform CAN drivers with Netlink support
                 CAN bit-timing calculation
                 TI High End CAN controller (HECC)

OMAP3x kernel

In the case of the Category:OMAP3x platform with a MCP2515 chip the configuration is:

Linux Kernel Configuration
     Networking support
        CAN bus subsystem support
           CAN device drivers
               Platform CAN drivers with Netlink support
                 CAN bit-timing calculation
                 Microchip MCP251x SPI CAN controller


Enable socketcan and ip tools

Working with the CAN bus requires enabling the 'ip' tools from iproute2 package (the 'ip' tool from busybox won't work). The socketcan package is optional and provide you with tools to debug your can bus.

These packages are available for selection from the RidgeRun SDK in the configuration menu.

 File System Configuration
   Select target's file system software
     iproute2-2.6.34 
     socketcan utils

Setup the networking rules

Edit your /etc/networking/interfaces on the target file system and add the following rules (required to setup the bit-rate of the bus):

auto can0
iface can0 inet manual
	#pre-up ip link set $IFACE type can bitrate 125000 listen-only off
	pre-up /ip link set $IFACE type can bitrate 125000 triple-sampling on
	up /sbin/ifconfig $IFACE up
	down /sbin/ifconfig $IFACE down

Verifying CAN support configuration

Linux boot

Look for the following in the Linux boot output

Run

dmesg | fgrep -i mcp

Expected output:

mcp251x spi1.0: setup: speed 750000, sample leading edge, clk normal
mcp251x spi1.0: setup mode 0, 8 bits/w, 1000000 Hz max --> 0
mcp251x spi1.0: CANSTAT 0x80 CANCTRL 0x07
mcp251x spi1.0: probed


Run

dmesg | fgrep -i can

Expected output:

PM: Adding info for No Bus:can0
CAN device driver interface
can: controller area network core (rev 20090105 abi 8)

sysfs entries

Verify the CAN host driver is registered correctly (meaning properly added to kernel arch/arm/mach-*/board-*.c file).

MC2515

Run:

ls -d /sys/bus/spi/drivers/mcp251x
cat /sys/devices/platform/omap2_mcspi.1/spi1.0/modalias
ls /sys/class/net/

Expect:

/sys/bus/spi/drivers/mcp251x
mcp2515
can0  eth0  lo

Power on CAN hardware

ip link set can0 type can bitrate 125000 triple-sampling on
ifconfig can0 up


Hints

No can0 interface

If you have problems with network interface can0 not being created, enable

kernel -> Device Drivers -> Generic Driver Options -> Driver Core verbose debug messages

and

kernel -> Networking support -> CAN bus subsystem support -> CAN Device Drivers -> CAN devices debugging messages

bit-timing calculation not available

Enable CAN bit-timing calculation in the Linux kernel.

kernel -> Networking support -> CAN bus subsystem support -> CAN Device Drivers -> CAN bit-timing calculation

MCP251x didn't wake-up

If the response to ifconfig can0 up is

mcp251x spi1.0: MCP251x didn't wake-up
mcp251x spi1.0: CNF: 0x03 0xf5 0x01

Then there is a problem with the interrupt signal from the MCP251x chip back to the driver. Check the arch/arm/mach-*/board-*.c file for your hardware along with any jumpers on your hardware design.

ip command says link/[280] instead of link/can

You need to enable and build iproute2 to get an up-to-date ip command that supports the can bus.


System files and command

Files

cat /proc/net/dev

Commands Examples

ip -details link show can0

References

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