Zephyr RTOS CAN TX/RX basic example

Application Description

The application aims at proposing a method to transmit and receive CAN frames with Zephyr RTOS.
More precisely, the application:

• Prints received CAN messages to the UART in this format: timestamp, CAN ID, DLC and data (e.g: [33258 ms] ID:0x010 DLC:1 DATA:00). CAN and UART are the default devices for the board used (refer to the board dts file).
• Is build time configurable for CAN baudrate, CAN messages transmit periods and CAN IDs.
• Sends three CAN messages with random data at build time defined periods.
• Starts printing when receiving a specific CAN message ID defined at build time (program starts immediately if the message is undefined).
• Stops printing when receiving a specific CAN message ID defined at build time (program never stops if the message is undefined).
• Prints 'Hello World' when receiving a specific CAN message ID defined at build time.
  
  

Warning: If the STOP printing message is defined but not the START one, it will never be possible to START printing again after a STOP message.

For a list of the build time configurable parameters, refer to the Kconfig files or to the Configurable parameters section below.

The tests folder features the unit tests for the application.

HOW TO

Prerequisites

The content of the application folder should be placed in your zephyrproject folder at zephyrproject/applications/zephyr_can_basic_example.

It should also be possible to use it from anywhere if the ZEPHYR_BASE environment variable is defined correctly and a west environment is activated. Refer to Zephyr documentation if needed: Zephyr Getting Started page.

Running the application on a board

Notes: The application has been tested with the NXP Freedom MCXN947 board, a PCAN Peak-USB adapter, the PCAN-View software and PuTTY serial terminal.

All the commands below are considered being run from zephyrproject/applications/zephyr_can_basic_example.

Building

west build -p always -b frdm_mcxn947/mcxn947/cpu0 .

The -p always option can be removed or change to avoid building everything from scratch.
The board name can be changed with the -b option if needed. The board name is also set in CMakeLists.txt to make it possible to remove the option from the command.
The build folder is generated in the application root folder.

Flashing

west flash

Drivers download might be needed for flashing.

Configuring

west build -t menuconfig -b frdm_mcxn947/mcxn947/cpu0 .
west flash # to apply the configuration

Running the tests

The tests are gathered in the tests folder.

Listing

west twister --list-tests -T tests/can_rx/

Building

west build -b native_sim tests/can_rx/ tests/can_rx/ --build-dir=tests/can_rx/build

The build folder is generated at tests/can_rx/build.

Running (locally)

west build -t run --build-dir=tests/can_rx/build

A Linux machine is expected to run the tests built with the -b native_sim option (Ubuntu WSL 24.04 on Windows 11 has been used during development). Otherwise, containers or virtual machines can be used.

Configuring

west build -t menuconfig -b native_sim tests/can_rx/ --build-dir=tests/can_rx/build

Configurable parameters

By running one of the commands below,

west build -t menuconfig -b frdm_mcxn947/mcxn947/cpu0 . # for application

west build -t menuconfig -b native_sim tests/can_rx/ --build-dir=tests/can_rx/build # for tests

following elements can be configured:

• CAN_TX1 sending period in ms: CAN_TX1_PERIOD_MS (default=50ms)
• CAN_TX1 message ID: CAN_TX1_ID (default=0x11)
• CAN_TX1 message DLC: CAN_TX1_DLC (default=1)
• CAN_TX2 sending period in ms: CAN_TX2_PERIOD_MS (default=250ms)
• CAN_TX2 message ID: CAN_TX2_ID (default=0x22)
• CAN_TX2 message DLC: CAN_TX2_DLC (default=4)
• CAN_TX3 sending period in ms: CAN_TX3_PERIOD_MS (default=500ms)
• CAN_TX3 message ID: CAN_TX3_ID (default=0x33)
• CAN_TX3 message DLC: CAN_TX3_DLC (default=8)
• Activation of START_MSG: START_MSG (default=true)
• ID of START_MSG if activated: START_MSG_ID (default=0x200)
• Activation of STOP_MSG: STOP_MSG (default=true)
• ID of STOP_MSG if activated: STOP_MSG_ID (default=0x201)
• Activation of HELLO_MSG: HELLO_MSG (default=true)
• ID of HELLO_MSG if activated: HELLO_MSG_ID (default=0x202)
• Bitrate of the CAN communication: CAN_BITRATE (default=500kbit/s)

The Kconfig file can be consulted for more information.

Scripts

Build and flash the app by running:

chmod +x scripts/app_build_flash.sh
./scripts/app_build_flash.sh

Build and run the tests by running:

chmod +x scripts/tests_build_run.sh
./scripts/tests_build_run.sh

Delete app and tests build folders by running:

chmod +x scripts/clean_build_folders.sh
./scripts/clean_build_folders.sh

TODO

• Linting and formating code.
• Optimize threads stack size.
• Implement twister to run tests.
• Improve code factorization if possible (wrap printk and can_send to make it mockable for unit tests).
• Is it possible/better to fuse the 3 TX threads with common code ?
• Make possible to configure more than just the CAN baurate in Kconfig.
• Implement a true random generator in the TX threads (see warning when building).
• Use logging (LOG_INF, LOG_ERR) instead of printk.
• Is it better to use timers than k_sleep in the TX threads ?
• Use realtime for timestamp (RTC).
• Complete unit tests with potentially CAN and UART mocking.
• Manage CAN errors.
  
  

Warnings: Depending on the evolution of the application's use cases, the value for the items below can become a problem:

• Threads stack size
• Threads priority
• CAN message RX queue size