The NXP i.MX6UL CPU has two FLEXCAN controllers which operate at up to 1Mbps. FlexCAN is a communications controller implementing the CAN protocol according to the CAN 2.0B protocol specification. It supports both standard and extended message frames, and the maximum message buffer is 64. The driver is a network device driver of PF_CAN protocol family.

You can access the CAN1 port through the expansion connector on the ConnectCore 6UL SBC Express.

On the ConnectCore 6UL SBC Pro:

  • CAN1 port lines are multiplexed with UART3 CTS/RTS.

  • CAN2 port lines are multiplexed with UART2 CTS/RTS.

  • Both CAN ports are accessible through a connector.

Kernel configuration

You can manage the CAN support through the kernel configuration options:

  • CAN Bus support (CONFIG_CAN)

  • NXP FlexCAN support (CONFIG_CAN_FLEXCAN)

These options are enabled as built-in on the default ConnectCore 6UL kernel configuration file.

Kernel driver

File Description

drivers/net/can/flexcan.c

FlexCAN driver

The CAN support is based on the SocketCAN stack. For more information and source code about this project, see http://elinux.org/CAN_Bus and https://github.com/linux-can/.

Device tree bindings and customization

The i.MX6UL CAN interface device tree binding is documented at Documentation/devicetree/bindings/net/can/fsl-flexcan.txt

Example: CAN1 on the ConnectCore 6UL SBC Pro

Definition of the device

i.MX6UL device tree
can1: flexcan@02090000 {
	compatible = "fsl,imx6ul-flexcan", "fsl,imx6q-flexcan";
	reg = <0x02090000 0x4000>;
	interrupts = <GIC_SPI 110 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&clks IMX6UL_CLK_CAN1_IPG>,
		    <&clks IMX6UL_CLK_CAN1_SERIAL>;
	clock-names = "ipg", "per";
	stop-mode = <&gpr 0x10 1 0x10 17>;
	status = "disabled";
};

IOMUX configuration

ConnectCore 6UL SBC Pro device tree
pinctrl_flexcan1: flexcan1grp{
	fsl,pins = <
		MX6UL_PAD_UART3_CTS_B__FLEXCAN1_TX	0x1b020
		MX6UL_PAD_UART3_RTS_B__FLEXCAN1_RX	0x1b020
	>;
};

Bus enabling

ConnectCore 6UL SBC Pro device tree
/* CAN1 (multiplexed with UART3 RTS/CTS) */
&can1 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_flexcan1>;
	xceiver-supply = <&ext_3v3>;
	status = "okay";
};

CAN user space usage examples

CAN device interface

The CAN driver is a network device driver from the PF_CAN protocol family. It exposes device data through the sysfs at /sys/class/net/canX/, where X is the port index, starting at zero.

Linux creates port indexes sequentially as enabled flexcan entries are found in the device tree.

For example, the default device tree configuration for ConnectCore 6UL SBC Pro has:

  • CAN1 enabled (set as can0 in Linux)

  • CAN2 disabled

Setting can1 status as "okay" in the device tree sets CAN1 as can0.

The CAN network device driver interface provides a generic interface to set up, configure, and monitor CAN network devices. For example, you can configure the CAN device via the netlink interface using the program ip from the iproute2 utility suite.

Configuring the interface

Before you can start the CAN network device, you must configure the bitrate at which it will communicate. In the following example, X is the index of the CAN node you want to configure:

~# ip link set canX up type can bitrate 125000

Starting and stopping the CAN network device

Similar to other network interfaces, you can start or stop a CAN network device with the ifconfig command. In the following example, X is the index of the CAN node you want to bring up or down.

To start:

~# ifconfig canX up

To stop:

~# ifconfig canX down

For more information, see the Linux kernel documentation: Documentation/networking/can.txt

Sample application

Example applications called apix-can-send-example and apix-can-recv-example are included in the dey-examples-digiapix recipe (part of dey-examples package) of meta-digi layer. These applications show how to send and receive packets through the CAN ports using Digi APIx library on the ConnectCore 6UL platform.

Go to GitHub to see the applications instructions and source code.

For example, to send an 8-bit CAN message to node can0 with ID 0x12 at a baudrate of 500 Kbit/s:

~# apix-can-send-example -i can0 -I 0x12 -b 5000000

To receive a similar message:

~# apix-can-recv-example -i can0 -b 5000000

See CAN API for more information about the CAN APIx.