Zephyr and Nordic nRF52-DK: debugging, unit testing, project analysis

The goal of this tutorial is to demonstrate how simple it is to use VSCode to develop, run and debug a simple Bluetooth project using Zephyr RTOS framework for the Nordic nRF52-DK board.

  • Level: Intermediate
  • Platforms: Windows, Mac OS X, Linux

Setting Up the Project

  1. Click on “PlatformIO Home” button on the bottom PlatformIO Toolbar:

  2. Click on “New Project”, select Nordic nRF52-DK as the development board, Zephyr RTOS as the framework and a path to the project location (or use the default one):


Adding Code to the Generated Project

  1. Create a new file main.c in src_dir folder and add the following code:

    // Copyright (c) 2015-2016 Intel Corporation
    // SPDX-License-Identifier: Apache-2.0
    #include <zephyr/types.h>
    #include <stddef.h>
    #include <sys/printk.h>
    #include <sys/util.h>
    #include <bluetooth/bluetooth.h>
    #include <bluetooth/hci.h>
    #define DEVICE_NAME_LEN (sizeof(DEVICE_NAME) - 1)
    // Set Advertisement data. Based on the Eddystone specification:
    // https://github.com/google/eddystone/blob/master/protocol-specification.md
    // https://github.com/google/eddystone/tree/master/eddystone-url
    static const struct bt_data ad[] = {
        BT_DATA_BYTES(BT_DATA_UUID16_ALL, 0xaa, 0xfe),
                  0xaa, 0xfe,
                  0x10, // Eddystone-URL frame type
                  0x00, // Calibrated Tx power at 0m
                  0x00, // URL Scheme Prefix http://www.
                  'z', 'e', 'p', 'h', 'y', 'r',
                  'p', 'r', 'o', 'j', 'e', 'c', 't',
                  0x08) // .org
    // Set Scan Response data
    static const struct bt_data sd[] = {
    static void bt_ready(int err)
        if (err) {
            printk("Bluetooth init failed (err %d)\n", err);
        printk("Bluetooth initialized\n");
        // Start advertising
        err = bt_le_adv_start(BT_LE_ADV_NCONN, ad, ARRAY_SIZE(ad),
                      sd, ARRAY_SIZE(sd));
        if (err) {
            printk("Advertising failed to start (err %d)\n", err);
        printk("Beacon started\n");
    void main(void)
        int err;
        printk("Starting Beacon Demo\n");
        // Initialize the Bluetooth Subsystem
        err = bt_enable(bt_ready);
        if (err) {
            printk("Bluetooth init failed (err %d)\n", err);
  2. By default Bluetooth feature is disabled, we can enable it by creating a new file prj.conf in zephyr folder and adding the following lines:

    CONFIG_BT_DEVICE_NAME="Test beacon"

Compiling and Uploading the Firmware

  1. To compile the project use one of the following options:

    • Build option from the Project Tasks menu
    • Build button in PlatformIO Toolbar
    • Task Menu Tasks: Run Task... > PlatformIO: Build or in PlatformIO Toolbar
    • Command Palette View: Command Palette > PlatformIO: Build
    • Hotkeys cmd-alt-b / ctrl-alt-b:
  2. If everything went well, we should see a successful result message in the terminal window:

  3. To upload the firmware to the board we can use the following options:

    • Upload option from the Project Tasks menu
    • Upload button in PlatformIO Toolbar
    • Command Palette View: Command Palette > PlatformIO: Upload
    • Task Menu Tasks: Run Task... > PlatformIO: Upload
    • Hotkeys cmd-alt-u / ctrl-alt-u:
  4. Connect the board to your computer and update the default monitor speed to 115200 in platformio.ini file:

    platform = sifive
    board = hifive1-revb
    framework = zephyr
    monitor_speed = 115200
  5. Open Serial Monitor to observe the output from the board:

  6. If everything went well, the board should be visible as a beacon:


Debugging the Firmware

Since Nordic nRF52-DK includes an onboard debug probe we can use PIO Unified Debugger without any configuration.

  1. To start a debug session we can use the following options:

    • Debug: Start debugging from the top menu
    • Start Debugging option from Quick Access menu
    • Hotkey button F5:
  2. We can walk through the code using control buttons, set breakpoints, add variables to Watch window:


Writing Unit Tests


Functions setUp and tearDown are used to initialize and finalize test conditions. Implementations of these functions are not required for running tests but if you need to initialize some variables before you run a test, you use the setUp function and if you need to clean up variables you use tearDown function.

For the sake of simplicity, let’s create a small library called calculator, implement several basic functions add, sub, mul, div and test them using PIO Unit Testing engine.

  1. PlatformIO uses a unit testing framework called Unity. Unity is not compatible with C library implemented in the framework. Let’s enable standard version of newlib C library in prj.conf file using the following config:

  2. Create a new folder calculator in the lib folder and add two new files calculator.h and calculator.c with the following contents:


    #ifndef _CALCULATOR_H_
    #define _CALCULATOR_H_
    #ifdef __cplusplus
    extern "C" {
    int add (int a, int b);
    int sub (int a, int b);
    int mul (int a, int b);
    int div (int a, int b);
    #ifdef __cplusplus
    #endif // _CALCULATOR_H_


    #include "calculator.h"
    int add(int a, int b)
        return a + b;
    int sub(int a, int b)
        return a - b;
    int mul(int a, int b)
        return a * b;
  3. Create a new file `test_calc.c to the folder test and add basic tests for calculator library:

    #include <calculator.h>
    #include <unity.h>
    void test_function_calculator_addition(void) {
        TEST_ASSERT_EQUAL(32, add(25, 7));
    void test_function_calculator_subtraction(void) {
        TEST_ASSERT_EQUAL(20, sub(23, 3));
    void test_function_calculator_multiplication(void) {
        TEST_ASSERT_EQUAL(50, mul(25, 2));
    void test_function_calculator_division(void) {
        TEST_ASSERT_EQUAL(32, div(100, 3));
    void main() {
  4. Let’s run tests on the board and check the results. There should be a problem with test_function_calculator_division test:

  5. Let’s fix the incorrect expected value, run tests again. After processing the results should be correct:


Project Inspection

For illustrative purposes, let’s imagine we need to find a function with the biggest memory footprint. Also, let’s introduce a bug to our project so PIO Check can report it.

  1. Open PlatformIO Home and navigate to Inspect section, select the current project and press Inspect button:

  2. Project statistics:

  3. The biggest function:

  4. Possible bugs:



Now we have a project template for Nordic Nordic nRF52-DK board that we can use as a boilerplate for the next projects.