How to configure and use CAN bus: Difference between revisions

Revision as of 05:47, 31 December 2010

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 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 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

MCP251x interrupt signal

MCP251x Platform Bus Data

In the architecture specific board file, such as arch/arm/mach-omap2/board-overo.c, first define the platform data:

#include <linux/can/platform/mcp251x.h>

static int overo_mcp2515_setup(struct spi_device *sdev)
{
	printk(KERN_DEBUG "overo_mcp2515_setup: Entry\n");
	return 0;
}

static int overo_mcp2515_transceiver_enable(int enable)
{
	printk(KERN_DEBUG "overo_mcp2515_transceiver_enable: Entry %d\n", enable);
	return 0;
}

static struct mcp251x_platform_data overo_mcp2515_pdata = {
	.oscillator_frequency   = 32*1000*1000,
	.board_specific_setup   = overo_mcp2515_setup,
	.model			= CAN_MCP251X_MCP2515,
	.power_enable           = overo_mcp2515_transceiver_enable,
};
<pre>

Then add the logic to initialize the GPIO used as the incoming mcp251x interrupt signal:

<pre>
static void __init overo_mcp251x_init(void)
{
	printk(KERN_DEBUG "overo_mcp251x_init: Entry\n");
	if ((gpio_request(OVERO_GPIO_CAN_INT, "MCP251x CAN INT") == 0) &&
	    (gpio_direction_input(OVERO_GPIO_CAN_INT) == 0)) {
		gpio_export(OVERO_GPIO_CAN_INT, 0);
		set_irq_type(OMAP_GPIO_IRQ(OVERO_GPIO_CAN_INT), IRQ_TYPE_EDGE_FALLING);
	} else {
		printk(KERN_ERR "could not obtain gpio for MCP251x CAN bus interrupt\n");
		return;
	}
}

Add the SPI information to the SPI board info array:

	{
		.modalias       = "mcp251x",
		.platform_data  = &overo_mcp2515_pdata,
		.irq            = OMAP_GPIO_IRQ(114),
		.max_speed_hz   = 1*1000*1000,
		.bus_num        = 1,
		.mode           = SPI_MODE_0,
		.chip_select    = 0,
	},

Finally call the GPIO interrupt initialization function right before registering SPI board info:

	overo_mcp251x_init();
	spi_register_board_info(overo_spi_board_info,
			ARRAY_SIZE(overo_spi_board_info));

GPIO MCP251x interrupt verification

You can use debugfs to monitor the GPIO used for the MCP251x interrupt signal.

Configure the kernel to enable debugfs:

Symbol: DEBUG_FS [=y]
   Prompt: Debug Filesystem
     Defined at lib/Kconfig.debug:77
     Depends on: SYSFS     
     Location:
       -> Kernel configuration
         -> Kernel hacking

Boot the target hardware and mount debugfs:

mount -t debugfs none /sys/kernel/debug

Check the current value and configuration for the GPIO of interest (for example GPIO 114):

fgrep 114 /sys/kernel/debug/gpio

with example output being:

gpio-114 (MCP251x CAN INT) in  hi irq-274 edge-falling

Which indicates GPIO 114 is configure as an input, currently has a high logic level, is mapped to IRQ 274, and causes an interrupt on the falling edge.

You can see if any interrupts have occurred using (for example GPIO 114 being mapped to IRQ 274):

fgrep 274 /proc/interrupts

with example output being:

274:  60        GPIO  mcp251x

which indicates 60 interrupts have been occurred.

Problems and how to resolve them

The titles of the following sections are text that gets displayed when a problem occurs. Each section describes how to resolve the issue.

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

bit-timing not yet defined

First run

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

then run

ifconfig can0 up

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

@@ Line 5: / Line 5: @@
 === AM35x kernel ===
-In the case of the [[:Category:AM35x]] platform the configuration is:
+In the case of the [[:Category:AM35x AM35x]] platform the configuration is:
   Linux Kernel Configuration
        Networking support
@@ Line 16: / Line 16: @@
 === OMAP3x kernel ===
-In the case of the [[:Category:OMAP3x]] platform with a MCP2515 chip the configuration is:
+In the case of the [[:Category:OMAP3x OMAP3x]] platform with a MCP2515 chip the configuration is:
   Linux Kernel Configuration
        Networking support
@@ Line 185: / Line 185: @@
 === GPIO MCP251x interrupt verification ===
-You can use debugfs to monitor the GPIO used for the MCP251x interrupt signal.
+You can use [http://lwn.net/Articles/334546/ debugfs] to monitor the GPIO used for the MCP251x interrupt signal.
 Configure the kernel to enable debugfs: