Developing applications for the nRF52832 using the nRF Connect SDK (NCS) involves more than just writing C code. Understanding the underlying build system is essential for efficient development, debugging, and deployment. Zephyr, the real-time operating system powering NCS, uses a combination of CMake and west to manage building, compiling, and flashing applications. In this post, we will explore how these tools interact, the configuration files that control your builds, and walk through an example of building and flashing a simple application on the nRF52832 development kit.
Understanding CMake and West in nRF Connect SDK
Zephyr OS, which forms the foundation of NCS, uses CMake as its build system generator. CMake is responsible for interpreting your project configuration and generating platform-specific build instructions. This can include Makefiles, Ninja build files, or other build scripts depending on your environment. CMake is extremely powerful because it allows Zephyr to abstract the complexities of cross-compilation, hardware-specific compilation flags, and linker scripts, letting developers focus on application logic rather than low-level build details.
While CMake handles the technical generation of build instructions, west serves as the project manager and orchestrator. West is a meta-tool designed specifically for Zephyr and nRF Connect SDK projects. Its responsibilities extend beyond simply invoking CMake. West manages multiple modules and repositories, ensuring that all the dependencies required for your application are available. It can fetch the Zephyr kernel, nRF-specific libraries, and external modules automatically. It also keeps track of versioning and ensures that all pieces of the SDK are compatible, reducing common errors that occur when projects are manually assembled.
When you run a west build command, west first ensures that the project environment is correctly set up. It locates Zephyr, configures the paths, and invokes CMake with the proper parameters. CMake then generates the build system tailored to your target hardware, resolves all dependencies, and produces a binary that can be flashed onto your nRF52832 development kit. This seamless integration between west and CMake is one of the reasons the nRF Connect SDK is highly efficient and reliable for embedded development.
Key Configuration Files in Zephyr
Developers working with nRF Connect SDK will frequently interact with several configuration files that dictate how an application is built and how it behaves at runtime. Among these, the most important are prj.conf, CMakeLists.txt, and the project manifest that west relies upon.
prj.conf
The prj.conf file, short for project configuration, defines which features of the Zephyr kernel and supporting libraries are enabled or disabled. It uses the Kconfig syntax, which is similar to how Linux kernel options are configured. Within this file, you can enable hardware drivers, configure memory sizes, or enable logging support. For example, a minimal configuration might look like this:
CONFIG_GPIO=y
CONFIG_UART_CONSOLE=y
CONFIG_LOG=y
Each line corresponds to a feature or kernel option. Enabling GPIO support allows the application to interact with digital pins on the nRF52832. Enabling the UART console provides a standard mechanism for printing log messages to a terminal. Enabling the Zephyr logging system allows for more sophisticated runtime diagnostics, which can be crucial for debugging and monitoring applications. The flexibility of prj.conf means you can tailor the system for a tiny footprint when needed, or enable full-featured debugging and peripheral support for more complex applications.
Another aspect of prj.conf is that it can control memory and stack sizes. Embedded systems often operate under tight memory constraints, and Zephyr allows you to explicitly define stack sizes for different threads, configure heap size, or enable system features such as real-time scheduling. This configurability ensures that the application remains efficient while still leveraging the capabilities of the hardware.
CMakeLists.txt
While prj.conf defines runtime features, the CMakeLists.txt file tells CMake how to compile your application. A typical Zephyr CMakeLists.txt is minimal, because Zephyr internally handles most build rules, compiler flags, and linker scripts. Here is an example of a simple CMakeLists.txt file:
cmake_minimum_required(VERSION 3.20.0)
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(hello_world)
target_sources(app PRIVATE src/main.c)
The find_package command ensures that CMake locates the Zephyr SDK, using the environment variable ZEPHYR_BASE if it is set. The project command names your application, which can be referenced in build outputs and logging. Finally, the target_sources command specifies which source files are included in the build. In Zephyr, all application code is compiled as part of the app target, which links against the Zephyr kernel and other selected libraries.
CMake also integrates seamlessly with device tree overlays and other hardware abstraction mechanisms provided by Zephyr. This means that you can define pin mappings, peripheral configurations, and other board-specific details in separate files, and CMake will include them automatically during the build process. For developers, this reduces the need to manually adjust compiler flags or linker scripts when targeting different boards.
West Build
west build is the command that ties everything together. When you invoke west build, west ensures that the build environment is properly set up, calls CMake with the correct configuration, and then triggers compilation. The command accepts several options, including the target board. For instance:
west build -b nrf52832dk_nrf52832
This command tells west to build the application for the nRF52832 development kit. By default, the build output is placed in a folder called build, but this can be customized. West also allows you to clean builds, rebuild only changed files, or rebuild from scratch using flags such as --pristine or -p auto.
Flashing the application is similarly straightforward. After a successful build, simply run:
west flash
West detects the programmer connected to your development board, usually a SEGGER J-Link, and writes the compiled binary to the nRF52832’s flash memory. This tight integration simplifies the development workflow, removing the need for manual compilation or programming commands.
Building and Flashing a Simple Application
To illustrate the process, let’s walk through building a simple “Hello World” application on the nRF52832. This example covers creating the project structure, writing the main application code, configuring runtime options, and finally building and flashing the program.
The project structure is minimal:
hello_world/
├── CMakeLists.txt
├── prj.conf
└── src/
└── main.c
Within main.c, the application might print a message to the console at regular intervals:
#include <zephyr.h>
#include <sys/printk.h>
void main(void)
{
printk("Hello, nRF52832!\n");
while (1) {
k_sleep(K_SECONDS(1));
}
}
This code uses the Zephyr printk function to print messages to the console. The infinite loop ensures the program continues running, while k_sleep provides a one-second delay between messages.
The prj.conf file for this project might include options to enable console output and configure stack sizes:
CONFIG_STDOUT_CONSOLE=y
CONFIG_MAIN_STACK_SIZE=1024
This configuration ensures that the console is active and allocates sufficient stack memory for the main thread. More advanced applications could expand prj.conf to include GPIO support, timers, or logging features.
To build the project, you would run:
west build -b nrf52832dk_nrf52832
West coordinates all dependencies, invokes CMake to generate the build system, and compiles the application. Once the build completes, flashing the binary to the board is as simple as:
west flash
Once flashed, the nRF52832 development kit begins running the program immediately. Using a terminal program like PuTTY or minicom, you can observe the “Hello, nRF52832!” messages appearing once every second.
Understanding the Build Output
After a build, the build folder contains several important artifacts. Among them are the compiled binary, map files, and intermediate build files. The binary, usually with a .hex or .elf extension, is what gets flashed to the hardware. Map files contain memory layout information, which can be useful for debugging or optimizing memory usage. Intermediate build files include object files, dependency graphs, and generated headers, which CMake uses to manage incremental builds efficiently.
Understanding the build output is crucial for more advanced development. For example, if you are integrating a new peripheral or library, inspecting the build logs can help you verify that the compiler is including the correct headers and source files. Similarly, map files provide insights into memory usage, which is particularly important on microcontrollers with limited RAM and flash storage like the nRF52832.
Why Zephyr’s Build System Matters
The Zephyr build system offers significant advantages over traditional embedded development workflows. By leveraging CMake and west, it provides a consistent, reproducible build environment across different platforms and operating systems. Developers no longer need to manually configure compiler flags, linker scripts, or manage multiple makefiles for different projects. Instead, most configuration is centralized in prj.conf and CMake handles the low-level build details.
Moreover, the integration of device tree overlays and Kconfig options means that the same codebase can target multiple boards with minimal changes. This makes it easier to scale applications from a single prototype board to a production device without rewriting large portions of code.
Tips for Effective Development
When working with Zephyr and the nRF Connect SDK, several practices can improve your workflow. Keeping your prj.conf organized and only enabling features you need helps minimize memory usage and compilation time. Using west’s --pristine or -p auto flags selectively can prevent unnecessary rebuilds, saving time during development. Familiarizing yourself with the build output, including map files and object files, aids in debugging and optimization. Finally, leveraging Zephyr’s logging and console output allows you to monitor application behavior in real time without additional hardware.
Conclusion
The Zephyr build system, powered by CMake and orchestrated by west, is a cornerstone of development on the nRF52832 with nRF Connect SDK. Understanding how these tools work, along with the roles of prj.conf and CMakeLists.txt, is essential for creating efficient and maintainable applications. With these fundamentals, you can quickly build, flash, and debug applications while taking full advantage of Zephyr’s features. The simple “Hello World” example demonstrates how straightforward the process is, but the principles scale to more complex projects, including those with multiple threads, peripherals, and advanced logging requirements.
Mastering the Zephyr build system sets the stage for more advanced topics, such as device tree overlays, logging strategies, debugging techniques, and peripheral driver integration. With this knowledge, you can confidently explore the full capabilities of the nRF52832 and the nRF Connect SDK.