Introduction to Zephyr RTOS#
The Zephyr OS is built on a lightweight kernel optimized for resource-constrained and embedded systems, making it an excellent fit for BeagleBoard projects. From simple environmental sensors and LED-based designs to advanced embedded controllers, smart devices, and IoT wireless applications. Zephyr is a scalable RTOS that can be used in multiple architectures and platforms.
This article will focus on giving a starting point to learning Zephyr using a Beagleboard.
Why Zephyr?#
Scalable: Zephyr is designed to be scalable, from simple embedded systems to complex IoT applications.
Modular: Zephyr is designed to be modular, allowing you to use only the components you need.
Open Source: Zephyr is open-source, allowing you to modify and contribute to the project.
Cross-platform: Zephyr supports multiple architectures and platforms.
Community: Zephyr has a large community of developers and contributors.
Getting Started with Zephyr#
To get started with Zephyr, you will need to follow Getting Started Guide by Zephyr. By following the guide, you will be able to set up your development environment and get to try out a zephyr sample applications.
Delving into Zephyr#
Once you have set up your development environment and tried out the sample applications, Let’s delve into Zephyr by creating a simple application. We will now delve into breaking the blinky sample application and understand how it works.
Here are the files in a simple Zephyr application:
Let’s pull blinky sample application from Zephyr repository to zephyrproject directory.
cp -r zephyrproject/zephyr/samples/basic/blinky zephyrproject/app
app
├── app.overlay
├── CMakeLists.txt
├── prj.conf
├─ src
| └── main.c
└── app.overlay
CMakeLists.txt: This file is used by CMake to build the application.
app.overlay: This file is used to configure the application changes based on the base device-tree.
prj.conf: This file is used to configure the Kconfig fragment that specifies application-specific values.
VERSION: This file is used to specify the version of the application.
src/main.c: This file contains the main application code.
Let’s take a look at the contents of the main.c file:
#include <stdio.h>
#include <zephyr/kernel.h>
#include <zephyr/drivers/gpio.h>
These include statements include the necessary header files for the application such as stdio.h for printf functions , kernel.h for kernel APIs like ms_sleep(), and gpio.h for GPIO APIs for GPIO related functions.
#define LED_NODE DT_ALIAS(led0)
As Zephyr uses a device tree to configure the hardware, this macro is used to get the device tree node for the LED by resolving the alias led0 alias present in the device tree, enabling the application to use the LED.
static const struct gpio_dt_spec led = GPIO_DT_SPEC_GET(LED0_NODE, gpios);
GPIO_DT_SPEC_GET fetches the GPIO configuration for led0.
Note
build error on this line means your board is unsupported.
if (!gpio_is_ready_dt(&led)) {
return 0;
}
This code checks if the GPIO is ready to use, if not it returns 0.
ret = gpio_pin_configure_dt(&led, GPIO_OUTPUT_ACTIVE);
This code configures the GPIO pin as an output pin and sets the initial state to active.
Note
There are many other options other than GPIO_OUTPUT_ACTIVE, like GPIO_OUTPUT_INACTIVE, GPIO_INPUT, etc. For more visit Zephyr GPIO API, GPIO input/output configuration flag section.
ret = gpio_pin_toggle_dt(&led);
The gpio_pin_toggle_dt API helps in toggling the LED’s state
k_msleep(1000);
This code makes the application sleep for 1000 milliseconds. part of the kernel API.
As you have seen in this sample, there was not a single bit of hardware-specific code. This is the beauty of Zephyr, which abstracts the hardware and provides a unified API
Building the Application#
To build the application, you need to run the following commands:
west build -b <board-name>.
Note
West is a tool that helps in managing multiple repositories and build systems. For more information, visit West documentation.
After building the application, you will get the zephyr.hex file in the build/zephyr directory.
Flashing the Application#
To flash the application, you need to run the following command:
west flash
Note
To use west flash in BeagleConnect Freedom or BeaglePlay, it requires
cc1352-flashertool to be installed.
pip3 install cc1352-flasher
- At the moment, BeagleBone AI-64 doesn’t support west flash. Please use the
AI-64 documentation provided by Zephyr for flashing the application.
- At the moment, BeagleV-Fire doesn’t support west flash. Please use the
BeagleV-Fire documentation provided by Zephyr for flashing the application.
Result#
After flashing the application, you will see the LED blinking every second.