CAN

Introduction to CAN

CAN (Controller Area Network) bus is a serial communication network that effectively supports distributed control or real-time control. The CAN bus is a bus protocol widely adopted in automobiles, designed for microcontroller communication in the automotive environment. For more information, you can refer to theCAN application report。

Hardware Connection

Wiring between CAN modules: CAN_H connects to CAN_H, CAN_L connects to CAN_L.

Communication Test

CAN Communication Test

You can test sending and receiving messages using the candump and cansend tools. Push the tools to the /system/bin/ directory for execution. The tools can be downloaded from github .

#Turn off the can0 device at both sending and receiving ends
ip link set can0 down
#Set the bitrate at both sending and receiving ends               
ip link set can0 up type can bitrate 1000000 dbitrate 3000000 fd on
#Execute candump at the receiving end, blocking while waiting for messages                               
candump can0
#Execute cansend at the sending end to send a message          
cansend can0 123#1122334455667788         

More Commands

1、 ip link set canX down           //Turn off the CAN device;
2、 ip link set canX up             //Turn on the CAN device;
3、 ip -details link show canX             //Display detailed information about the CAN device;
4、 candump canX                    //Receive data sent from the CAN bus;
5、 ifconfig canX down                     //Turn off the CAN device for configuration;
6、 ip link set canX up type can bitrate 1000000 //Set the CAN baud rate
7、 conconfig canX bitrate + baud rate；
8、 canconfig canX start            //Start the CAN device;
9、 canconfig canX ctrlmode loopback on //Loopback test;
10、canconfig canX restart          // Restart the CAN device;
11、canconfig canX stop             //Stop the CAN device;
12、canecho canX                    //Check the CAN bus status;
13、cansend canX --identifier=ID+data      //Send data;
14、candump canX --filter=ID：mask   //Use a filter to receive data matching the ID

FAQS

A summary of several issues encountered during debugging and their solutions:

Messages are received long after being sent, or not received at all.

Check the CAN_H and CAN_L bus lines to see if the Dupont wires are loose or reversed.

CAN Clock Frequency Configuration

CAN

If the CAN bitrate is 1M, it is recommended to change the CAN clock to 300M for a more stable signal. For bitrates below 1M, a clock setting of 200M is sufficient.

Modifying CAN Clock Frequency

The method for modifying the CAN clock frequency is as follows:

diff --git a/kernel/arch/arm64/boot/dts/rockchip/rk3568-evb.dtsi b/kernel/arch/arm64/boot/dts/rockchip/rk3568-evb.dtsi
index b9df07be8..6b20e2eba 100644
--- a/kernel/arch/arm64/boot/dts/rockchip/rk3568-evb.dtsi
+++ b/kernel/arch/arm64/boot/dts/rockchip/rk3568-evb.dtsi
@@ -252,7 +252,7 @@ wireless_bluetooth: wireless-bluetooth {
 
 &can1 {
        assigned-clocks = <&cru CLK_CAN1>;
-       assigned-clock-rates = <150000000>;
+       assigned-clock-rates = <100000000>;
        pinctrl-names = "default";
        pinctrl-0 = <&can1m1_pins>;
        status = "disabled";
@@ -260,7 +260,7 @@ wireless_bluetooth: wireless-bluetooth {
 
 &can2 {
        assigned-clocks = <&cru CLK_CAN2>;
-       assigned-clock-rates = <150000000>;
+       assigned-clock-rates = <100000000>;
        pinctrl-names = "default";
        pinctrl-0 = <&can2m1_pins>;
        status = "disabled";

Note：

At certain clock frequencies, the CAN bitrate may not achieve the exact rate. You can adjust the assigned-clock-rates to solve this. To check if the desired bitrate is obtained:

ip -d link show can1