How to configure and use CAN bus
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.
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