Covid-19: Bootlin proposes online sessions for all its courses

Tux working on embedded Linux on a couchLike most of us, due to the Covid-19 epidemic, you may be forced to work from home. To take advantage from this time confined at home, we are now proposing all our training courses as online seminars. You can then benefit from the contents and quality of Bootlin training sessions, without leaving the comfort and safety of your home. During our online seminars, our instructors will alternate between presentations and practical demonstrations, executing the instructions of our practical labs.

At any time, participants will be able to ask questions.

We can propose such remote training both through public online sessions, open to individual registration, as well as dedicated online sessions, for participants from the same company.

Public online sessions

We’re trying to propose time slots that should be manageable from Europe, Middle East, Africa and at least for the East Coast of North America. All such sessions will be taught in English. As usual with all our sessions, all our training materials (lectures and lab instructions) are freely available from the pages describing our courses.

Our Embedded Linux and Linux kernel courses are delivered over 7 or 8 half days of 4 hours each, while our Yocto Project, Buildroot and Linux Graphics courses are delivered over 4 half days of 4 hours each.

Here are all the available sessions. If the situation lasts longer, we will create new sessions as needed:

Type Dates Time Duration Expected trainer Cost and registration
Embedded Linux (agenda) Jul. 27, 28, 29, 30, Aug. 3, 4, 5, 2020 17:00 – 21:00 (Paris), 8:00 – 12:00 (San Francisco) 28 h Michael Opdenacker 829 EUR + VAT* (register)
Yocto Project (agenda) Jul, 28, 29, 30, 31, 2020 9:00 – 13:00 (Paris time) 16 h Alexandre Belloni 519 EUR + VAT* (register)
Buildroot (agenda) Jul. 28, 29, 30, 31, 2020 9:00 – 13:00 (Paris time) 16 h Thomas Petazzoni 519 EUR + VAT* (register)
Linux kernel (agenda) September 14, 15, 16, 17, 18, 21 and 22, 2020 13:30 – 17:30 (Paris time) 28 h Gregory Clement 829 EUR + VAT* (register)
Linux Graphics (agenda) Sep. 22, 23, 24 and 25, 2020 14:00 – 18:00 (Paris time) 16 h Paul Kocialkowski 519 EUR + VAT* (register)

* VAT: applies to businesses in France and to individuals from all countries. Businesses in the European Union won’t be charged VAT only if they provide valid company information and VAT number to Evenbrite at registration time. For businesses in other countries, we should be able to grant them a VAT refund, provided they send us a proof of company incorporation before the end of the session.

Each public session will be confirmed once there are at least 6 participants. If the minimum number of participants is not reached, Bootlin will propose new dates or a full refund (including Eventbrite fees) if no new date works for the participant.

We guarantee that the maximum number of participants will be 12.

Dedicated online sessions

If you have enough people to train, such dedicated sessions can be a worthy alternative to public ones:

  • Flexible dates and daily durations, corresponding to the availability of your teams.
  • Confidentiality: freedom to ask questions that are related to your company’s projects and plans.
  • If time left, possibility to have knowledge sharing time with the instructor, that could go beyond the scope of the training course.
  • Language: possibility to have a session in French instead of in English.

Online seminar details

Each session will be given through Jitsi Meet, a Free Software solution that we are trying to promote. As a backup solution, we will also be able to Google Hangouts Meet. Each participant should have her or his own connection and computer (with webcam and microphone) and if possible headsets, to avoid echo issues between audio input and output. This is probably the best solution to allow each participant to ask questions and write comments in the chat window. We also support people connecting from the same conference room with suitable equipment.

Each participant is asked to connect 15 minutes before the session starts, to make sure her or his setup works (instructions will be sent before the event).

How to register

For online public sessions, use the EventBrite links in the above list of sessions to register one or several individuals.

To register an entire group (for dedicated sessions), please contact and tell us the type of session you are interested in. We will then send you a registration form to collect all the details we need to send you a quote.

You can also ask all your questions by calling +33 484 258 097.

Questions and answers

Q : Should I order hardware in advance, our hardware included in the training cost?
R : No, practical labs are replaced by technical demonstrations, so you will be able to follow the course without any hardware. However, you can still order the hardware by checking the “Shopping list” pages of presentation materials for each session. This way, between each session, you will be able to replay by yourself the labs demonstrated by your trainer, ask all your questions, and get help between sessions through our dedicated Matrix channel to reach your goals.

Q: Why just demos instead of practicing with real hardware?
A: We are not ready to support a sufficient number of participants doing practical labs remotely with real hardware. This is more complicated and time consuming than in real life. Hence, what we we’re proposing is to replace practical labs with practical demonstrations shown by the instructor. The instructor will go through the normal practical labs with the standard hardware that we’re using.

Q: Would it be possible to run practical labs on the QEMU emulator?
R: Yes, it’s coming. In the embedded Linux course, we are already offering instructions to run most practicall labs on QEMU between the sessions, before the practical demos performed by the trainer. We should also be able to propose such instructions for our Yocto Project and Buildroot training courses in the next months. Such work is likely to take more time for our Linux kernel course, practical labs being closer to the hardware that we use.

Q: Why proposing half days instead of full days?
A: From our experience, it’s very difficult to stay focused on a new technical topic for an entire day without having periodic moments when you are active (which happens in our public and on-site sessions, in which we interleave lectures and practical labs). Hence, we believe that daily slots of 4 hours (with a small break in the middle) is a good solution, also leaving extra time for following up your normal work.

Bootlin at FOSDEM and Buildroot Developers Meeting

FOSDEM 2020This week-end takes place one of the biggest and most important free and open-source software conference in Europe: FOSDEM. It will once again feature a very large number of talks, organized in several main tracks and developer rooms.

Bootlin CTO Thomas Petazzoni will participate to the FOSDEM conference, of course attending many of the talks from the Embedded, Mobile and Automative Devroom, to which he participated to the talk review and selection. Do not hesitate to get in touch with Thomas if you want to discuss career or business opportunities with Bootlin.

In addition, Thomas will also participate to the 3-day Buildroot Developers meeting which takes place in Brussels right after the FOSDEM conference, kindly hosted by Google. During 3 days, some of the core Buildroot developers will work together to discuss the future of Buildroot, as well as review and discuss pending patches and proposals.

Building a Linux system for the STM32MP1: developing a Qt5 graphical application

After showing how to build a minimal Linux system for the STM32MP157 platform, how to connect and use an I2C based pressure/temperature/humidity sensor and how to integrate Qt5 in our system, how to set up a development environment to write our own Qt5 application, we are finally going to write our Qt5 application.

List of articles in this series:

  1. Building a Linux system for the STM32MP1: basic system
  2. Building a Linux system for the STM32MP1: connecting an I2C sensor
  3. Building a Linux system for the STM32MP1: enabling Qt5 for graphical applications
  4. Building a Linux system for the STM32MP1: setting up a Qt5 application development environment
  5. Building a Linux system for the STM32MP1: developing a Qt5 graphical application
  6. Building a Linux system for the STM32MP1: implementing factory flashing
  7. Building a Linux system for the STM32MP1: remote firmware updates


Before we get started in this blog post, it is important to mention that it is not meant to be a full introduction to programming applications with Qt5. This would require much more than a blog post, and the Qt web site has extensive documentation.

Also, we want to make it clear that Bootlin’s core expertise is in low-level embedded Linux development, not in Qt application development. Therefore, our example application may not show the best practices in terms of Qt development. We welcome comments and suggestions from our readers to improve the example used in this blog post.

Reading sensor data

As we’ve seen in a previous article, the sensor data is available by reading the following files:

  • /sys/bus/iio/devices/iio:device2/in_temp_input for the temperature
  • /sys/bus/iio/devices/iio:device2/in_pressure_input for the pressure
  • /sys/bus/iio/devices/iio:device2/in_humidityrelative_input for the humidity

So what we will do is writing a new class called DataProvider, which will read those files once per second, and emit a signal with the 3 values every second. Slots and signals is a fundamental mechanism in Qt, which allows to connect emitters of events to receivers for those events. In our case, the DataProvider class will emit a signal when new sensor values are read, while another class in charge of the graphical UI will receive those signals.

At this step, we don’t yet have a graphical UI, so we’ll simply add a few debugging messages in the DataProvider to make sure it works as expected.

Let’s start by adding a data-provider.h file to our project:


#include <QtCore/QTimer>

class DataProvider: public QObject


private slots:
    void handleTimer();

    void valueChanged(float temp, float pressure, float humidity);

    QTimer timer;

#endif /* DATA_PROVIDER_H */

It creates a very simple class than inherits from QObject, with:

  • A constructor
  • A private slot handleTimer which will be used internally by the class QTimer’s instance to notify that a timer has expired. This is what will allow us to poll the sensor values every second.
  • A valueChanged signal, which will be emitted by the class every time new sensor values are available.

Then, the implementation of this class in data-provider.cpp is fairly straight-forward:

#include <QtCore/QFile>
#include <QDebug>
#include "data-provider.h"

    QObject::connect(&timer, &QTimer::timeout,
		     this, &DataProvider::handleTimer);

void DataProvider::handleTimer()
    QFile temp_f("/sys/bus/iio/devices/iio:device2/in_temp_input");
    QFile pressure_f("/sys/bus/iio/devices/iio:device2/in_pressure_input");
    QFile humidity_f("/sys/bus/iio/devices/iio:device2/in_humidityrelative_input");

    if (! | QIODevice::Text))
    if (! | QIODevice::Text))
    if (! | QIODevice::Text))

    float temp = QString(temp_f.readAll()).toDouble() / 1000;
    float pressure = QString(pressure_f.readAll()).toDouble() * 10;
    float humidity = QString(humidity_f.readAll()).toDouble() / 1000;

    qDebug() << "Temperature: " << temp << "Pressure: " << pressure << "Humidity: " << humidity;

    emit valueChanged(temp, pressure, humidity);

The constructor of the class connects the QTimer::timeout signal of the QTimer to this class handlerTimer slot, sets the timer interval to 1000 milliseconds, and starts the timer. This is what will ensure the handleTimer method gets called every second.

In the handleTimer method, we open the 3 files in sysfs, read their value and convert them to meaningful units: the temperature in Celcius, the pressure in hPA, and the humidity in percent. We then print a debugging message and emit the signal with the three values.

With this in place, we need to make sure those two files are properly taken into account by our project, by changing the .pro file as follows:

QT += widgets
SOURCES = main.cpp data-provider.cpp
HEADERS = data-provider.h
INSTALLS += target
target.path = /usr/bin

The data-provider.cpp file was added to SOURCES, while data-provider.h was added to the new HEADERS.

Now, we just need to change main.cpp to instantiate one DataProvider object:

#include <QApplication>
#include <QPushButton&ht;
#include "data-provider.h"

int main(int argc, char* argv[])
    QApplication app(argc, argv);
    QPushButton hello("Hello world!");
    DataProvider dp;
    return app.exec();

With this, you can now build and run the application, and you should see every second the debugging message showing the temperature, pressure and humidity values:

# qt-sensor-demo -platform linuxfb
Temperature:  28.12  Pressure:  1003.08  Humidity:  32.235
Temperature:  28.12  Pressure:  1003.07  Humidity:  32.246
Temperature:  28.12  Pressure:  1003.06  Humidity:  32.256
Temperature:  28.12  Pressure:  1003.08  Humidity:  32.267

Displaying sensor data

We now want to display the sensor data. For this, we'll create a UI with two panels, one to display the numeric value of the temperature, humidity and pressure, and another panel with a chart of the temperature. At the bottom of the screen, two buttons Values and Chart will allow to switch between both panels.

So, we'll create a Window class to encapsulate the overall window layout and behavior, and a Values class providing the widget showing the 3 values. We'll leave the chart implementation to the next section. To help you follow the code in this section, here is a diagram that shows the different widgets and how they will be grouped together in our user interface:

Qt Sensor demo UI

Let's start by implementing the Values widget, which will be used to show the 3 numeric values, one below each other. The values.h file will look like this:

#ifndef VALUES_H
#define VALUES_H

#include <QWidget>

class QLabel;

class Values : public QWidget


public slots:
    void handleValueChanged(float temp, float pressure, float humidity);

    QLabel *temperature_v;
    QLabel *pressure_v;
    QLabel *humidity_v;

#endif /* VALUES_H */

So it has a simple constructor, a slot to be notified of new values available, and 3 text labels to display the 3 values. The implementation in values.cpp is:

// SPDX-License-Identifier: MIT
#include <QtWidgets>
#include "values.h"

    QVBoxLayout *layout = new QVBoxLayout;

    QLabel *temperature_l = new QLabel(tr("Temperature (°C)"));
    QLabel *pressure_l = new QLabel(tr("Pressure (hPa)"));
    QLabel *humidity_l = new QLabel(tr("Humidity (%)"));

    temperature_v = new QLabel();
    pressure_v = new QLabel();
    humidity_v = new QLabel();

    QFont f = temperature_v->font();
    temperature_v->setAlignment(Qt::AlignRight | Qt::AlignVCenter);
    pressure_v->setAlignment(Qt::AlignRight | Qt::AlignVCenter);
    humidity_v->setAlignment(Qt::AlignRight | Qt::AlignVCenter);



void Values::handleValueChanged(float temp, float pressure, float humidity)
    temperature_v->setText(QString::number(temp, 'f', 2));
    pressure_v->setText(QString::number(pressure, 'f', 1));
    humidity_v->setText(QString::number(humidity, 'f', 1));

The constructor creates 3 text labels for the legends ("Temperature (°C)", "Pressure (hPA)" and "Humidity (%)"), then instantiates the 3 text labels for the values themselves. It sets up the font and text alignment properties for those labels, and then adds all widgets in a QVBoxLayout so that they all appear vertically below each other.

The handleValueChanged slot simply updates the text labels contents with the new sensor values, doing the proper text formatting on the way.

With the Values class implemented, we can now implement the main Window class. The window.h will contain:

#ifndef WINDOW_H
#define WINDOW_H

#include <QWidget>

class Values;

class Window : public QWidget

public slots:
    void handleValueChanged(float temp, float pressure, float humidity);


    Values *values;


Beyond a simple constructor, it has a slot to receive new sensor values, and a reference to a Values widget instance.

The implementation in window.cpp is as follows:

#include <QtWidgets>

#include "window.h"
#include "values.h"

    values = new Values;
    QVBoxLayout *layout = new QVBoxLayout;
    QHBoxLayout *buttons = new QHBoxLayout;

    QPushButton *values_button = new QPushButton("Values");
    QPushButton *chart_button = new QPushButton("Chart");





void Window::handleValueChanged(float temp, float pressure, float humidity)
    values->handleValueChanged(temp, pressure, humidity);

The constructor creates a horizontal layout QHBoxLayout with two buttons: Values and Chart. Those will be used in the next section to switch between the Values panel and the Chart panel. For now, they don't do anything.

Then, the constructor adds the Value widget, and the horizontal layout box with the buttons into a vertical box layout, assigns the main window layout and defines the window title.

The handleValueChanged slot implementation just forwards the call to the Values::handleValueChanged method.

Now, obviously main.cpp needs to be changed: instead of creating a button, we'll create our window, and do a bit of additional setup:

#include <QApplication>
#include "window.h"
#include "data-provider.h"

int main(int argc, char* argv[])
    QApplication app(argc, argv);
    DataProvider dp;
    Window window;

    QObject::connect(&dp, &DataProvider::valueChanged,
		     &window, &Window::handleValueChanged);

    window.setFixedSize(480, 800);
    window.setStyleSheet("background-color: white;");;
    return app.exec();

So, not only we create the Window, but more importantly, we connect the valueChanged signal of DataProvider to the handleValueChanged slot of Window. We define the window size (which is fixed, to match the STM32MP15 Discovery board panel) and set the background color of the application.

Obviously, the file needs to be adjusted to build our new files. It now looks like this:

QT += widgets
SOURCES = main.cpp data-provider.cpp window.cpp values.cpp
HEADERS = data-provider.h window.h values.h
INSTALLS += target
target.path = /usr/bin

With this done, we can run the Qt5 application on our target, and see:

Qt5 application showing the I2C sensor data

Graphing the temperature

The final part of developing our application is to implement a graph showing the evolution of temperature over time. For this, we are going to use the very convenient Qt Charts module, which is available in a separate Qt module from the base of Qt.

To implement the graph widget itself, we'll create a new Chart class:

#ifndef CHART_H
#define CHART_H

#include <QtCharts/QChart>

class QSplineSeries;
class QValueAxis;


class Chart: public QChart

    Chart(QGraphicsItem *parent = 0, Qt::WindowFlags wFlags = 0);

public slots:
    void handleValueChanged(float temp, float pressure, float humidity);

    QSplineSeries *m_series;
    QStringList m_titles;
    QValueAxis *m_axisX;
    QValueAxis *m_axisY;
    int xpos;

#endif /* CHART_H */

This class inherits from the QChart class provided by Qt. It provides a constructor and destructor, a slot that allows to receive notification of new sensor values, and it has a number of private variables to manage the chart itself.

Let's go through the implementation of this class now:

#include "chart.h"
#include <QtCharts/QAbstractAxis>
#include <QtCharts/QSplineSeries>
#include <QtCharts/QValueAxis>

Chart::Chart(QGraphicsItem *parent, Qt::WindowFlags wFlags):
    QChart(QChart::ChartTypeCartesian, parent, wFlags),
    m_axisX(new QValueAxis()),
    m_axisY(new QValueAxis()),
    m_series = new QSplineSeries(this);
    QPen pen(Qt::red);
    m_series->append(xpos, 30);


    m_axisX->setRange(0, 60);
    m_axisY->setRange(0, 50);

    QFont f = m_axisX->labelsFont();


    setTitle("Temperature (°C)");

void Chart::handleValueChanged(float temp, float pressure, float humidity)
    m_series->append(xpos, temp);
    if (xpos >= 60)
      scroll(plotArea().width() / 60, 0);

The constructor simply sets up the QChart we inherit from: defining the axis, their range, the pen width and color, etc. On the X axis (time), we are going to show 60 measurements, and since our handleValueChanged slot is going to be called every second, it means our graph will show the last 60 seconds of temperature measurement. On the Y axis (temperature), we can show temperatures from 0°C to 50°C. Of course, this is all very hardcoded in this example, for simplicity.

The handleValueChanged slot appends the new temperature value to the graph, and then updates the area displayed by the graph so that always the last 60 seconds are visible.

Now, we need to integrate this to our existing Window class, so that we can display the chart, and switch between the numeric values and the chart. First, we need to do some changes in window.h, and below we'll show only the diff to make the differences very clear:

diff --git a/window.h b/window.h
index 3d63d38..05d1f39 100644
--- a/window.h
+++ b/window.h
@@ -3,8 +3,12 @@
 #define WINDOW_H
 #include <QWidget>
+#include <QtCharts/QChartView>
 class Values;
+class Chart;
 class Window : public QWidget
@@ -13,11 +17,17 @@ class Window : public QWidget
 public slots:
     void handleValueChanged(float temp, float pressure, float humidity);
+private slots:
+    void chartButtonClicked();
+    void valuesButtonClicked();
     Values *values;
+    QChartView *chartView;
+    Chart *chart;

So, we're defining two private slots that will be used for the two buttons that allow to switch between the numeric values and the chart, and then we add two variables, one for the chart itself, and one for the QChartView (which basically renders the graph into a widget).

Then, in window.cpp, we do the following changes:

diff --git a/window.cpp b/window.cpp
index aba2862..d654964 100644
--- a/window.cpp
+++ b/window.cpp
@@ -3,28 +3,54 @@
 #include "window.h"
 #include "values.h"
+#include "chart.h"
     values = new Values;
+    chart = new Chart;
     QVBoxLayout *layout = new QVBoxLayout;
     QHBoxLayout *buttons = new QHBoxLayout;
     QPushButton *values_button = new QPushButton("Values");
     QPushButton *chart_button = new QPushButton("Chart");
+    QObject::connect(chart_button, &QPushButton::clicked,
+                    this, &Window::chartButtonClicked);
+    QObject::connect(values_button, &QPushButton::clicked,
+                    this, &Window::valuesButtonClicked);
+    chartView = new QChartView(chart);
+    chartView->setRenderHint(QPainter::Antialiasing);
+    layout->addWidget(chartView);
+    chartView->hide();
 void Window::handleValueChanged(float temp, float pressure, float humidity)
     values->handleValueChanged(temp, pressure, humidity);
+    chart->handleValueChanged(temp, pressure, humidity);
+void Window::chartButtonClicked()
+    values->hide();
+    chartView->show();
+void Window::valuesButtonClicked()
+    values->show();
+    chartView->hide();

So, in the constructor we are connecting the clicked signals of the two buttons to their respective slots. We create the Chart object, and then the QChartView to render the graph. We add the latter as an additional widget in the QVBoxLayout, and we hide it.

The existing handleValueChanged slot is modified to also update the Chart object with the new sensor values.

Finally, the new chartButtonClicked and valuesButtonClicked slots implement the logic that is executed when the buttons are pressed. We simply hide or show the appropriate widget to display either the numeric values or the chart. There is probably a nicer way to achieve this in Qt, but this was good enough for our example.

Now that the source code is in place, we of course need to adjust the build logic in

--- a/
+++ b/
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: MIT
-QT += widgets
-SOURCES = main.cpp data-provider.cpp window.cpp values.cpp
-HEADERS = data-provider.h window.h values.h
+QT += widgets charts
+SOURCES = main.cpp data-provider.cpp window.cpp values.cpp chart.cpp
+HEADERS = data-provider.h window.h values.h chart.h
 INSTALLS += target
 target.path = /usr/bin

Besides the obvious addition of the chart.cpp and chart.h file, the other important addition is charts to the QT variable. This tells qmake that our application is using the Qt Charts, and that we therefore need to link against the appropriate libraries.

Building the application

At this point, if you try to build the application, it will fail because QtCharts has not been built as part of our Buildroot configuration. In order to address this, run Buildroot's make menuconfig, enable the BR2_PACKAGE_QT5CHARTS option (in Target packages -> Graphic libraries and applications -> Qt5 -> qt5charts).

Then, run the Buildroot build with make, and reflash the resulting SD card image.

Now, you can build again your application, either with Qt Creator if you've been using Qt Creator, or manually. If you build it manually, you'll have to run qmake again to regenerate the Makefile, and then build with make.

When you run the application on the target, the GUI will display the same numeric values as before, but now if you press the Chart button, it will show something like:

Qt5 application with chart

Adjusting the Buildroot package

We have for now been building this application manually, but as explained in our previous blog post, we really want Buildroot to be able to build our complete system, including our application. For this reason, we had created a qt-sensor-demo package, which gets our application source code, configures it with qmake, builds it and installs it.

However, with the new use of Qt Charts, our qt-sensor-demo package needs a few adjustements:

  • The file needs an additional select BR2_PACKAGE_QT5CHARTS, to make sure Qt Charts are enabled in the Buildroot configuration
  • The file needs an additional qt5charts in the QT_SENSOR_DEMO_DEPENDENCIES variable to make sure the qt5charts package gets built before qt-sensor-demo

With this in place, you can run:

make qt-sensor-demo-rebuild

And you have an SD card image that includes our application!

Starting the application automatically at boot time

The next and almost final step for this blog post is to get our application automatically started at boot time. We can simply add a small shell script on the target in /etc/init.d/: the default Buildroot configuration for the init system will execute all scripts named Ssomething in /etc/init.d/. We'll add a file named package/qt-sensor-demo/S99qt-sensor-demo with these contents:


DAEMON_ARGS="-platform linuxfb"

start() {
	printf 'Starting %s: ' "$DAEMON"
	start-stop-daemon -b -m -S -q -p "$PIDFILE" -x "/usr/bin/$DAEMON" -- $DAEMON_ARGS
	if [ "$status" -eq 0 ]; then
		echo "OK"
		echo "FAIL"
	return "$status"

stop () {
	printf 'Stopping %s: ' "$DAEMON"
	start-stop-daemon -K -q -p "$PIDFILE"
	if [ "$status" -eq 0 ]; then
		rm -f "$PIDFILE"
		echo "OK"
		echo "FAIL"
	return "$status"

restart () {
	sleep 1

case "$1" in
		# Restart, since there is no true "reload" feature.
                echo "Usage: $0 {start|stop|restart|reload}"
                exit 1

This is the canonical init script used in Buildroot to start system daemons and services, and is modeled after the one in package/busybox/S01syslogd. It uses the start-stop-daemon program to start our application in the background.

Then, to get this init script installed, we need to adjust package/qt-sensor-demo/ with the following additional lines:

        $(INSTALL) -D -m 755 package/qt-sensor-demo/S99qt-sensor-demo \

This ensures that the init script gets installed in /etc/init.d/S99qt-sensor-demo as part of the build process of our qt-sensor-demo package. Note that an init script works fine if you're using the Busybox init implementation or the sysvinit init implementation (we're using the default Buildroot setup here, which uses the Busybox init implementation). If you want to use systemd as an init implementation, then a different setup is necessary.

With this done, you simply need to reinstall the application and regenerate the SD card image

$ make qt-sensor-demo-reinstall
$ make

You can now test your SD card image on you board, and you should see the application being started automatically, with the following messages at boot time

Starting dropbear sshd: OK
Starting qt-sensor-demo: OK

Welcome to Buildroot

Avoid unnecessary logging on the display panel

In our current setup, the kernel messages are being sent to both the serial port and the framebuffer console, which means they appear on the display panel. This is not very pretty, and we would like the display to remain black until the application starts, while keeping the kernel messages on the serial port for debugging purposes. Also, we would like the framebuffer console text cursor to not be displayed, to really have a fully black screen. To achieve this we will add two arguments on the Linux kernel command line:

  • console=ttySTM0,115200, which will tell the Linux kernel to only use the serial port as the console, and not all registered consoles, which would include the framebuffer console. This option will make sure the kernel messages are not displayed on the screen.
  • vt.global_cursor_default=0, which will tell the Linux kernel to not display any cursor on the framebuffer console.

So, to add those options, we simply modify board/stmicroelectronics/stm32mp157-dk/overlay/boot/extlinux/extlinux.conf in Buildroot as follows:

label stm32mp15-buildroot
  kernel /boot/zImage
  devicetree /boot/stm32mp157c-dk2.dtb
  append root=/dev/mmcblk0p4 rootwait console=ttySTM0,115200 vt.global_cursor_default=0

Of course, rebuild the SD card image with make, reflash and test the result on your STM32MP1 platform.


In this blog post, we have seen how to write a real (but admittedly very simple) Qt application, how to make it read and display sensor data, and how to integrate this application so that it gets started at boot time.

You can find the Buildroot changes corresponding to this blog post in the 2019.02/stm32mp157-dk-blog-5 branch of our repository. The qt-sensor-demo application code can be found in the blog-5 branch of this application Git repository.

Stay tuned for our next blog post about factory flashing and OTA update!

Improvements to Buildroot maintenance tooling

From mid-April to end of August, Victor Huesca, a student from the University of Toulouse joined Bootlin’s team for a 3.5 months internship. His internship was focused on the Buildroot project, and Victor’s mission was to improve various aspect of the tooling around Buildroot to help in the maintenance of this build system. In this blog post, we will present the different improvements and features implemented by Victor during his internship. This internship was funded by Bootlin, and entirely focused on contributing to the Buildroot project.

Notifications of new upstream versions of packages

Buildroot has over 2400 packages for a wide variety of software components, and it is a challenge to keep all of those packages updated with the latest releases from the upstream developers. Buildroot has a nice statistics page with all its packages, and in early 2019, your author added support for querying the service to find the latest upstream version of each package. This allowed our statistics page to show the current version in Buildroot and the latest version available upstream for all Builroot packages.

Victor improved this by implementing e-mail notifications to Buildroot developers about their package having new upstream releases available. Indeed, Buildroot has a DEVELOPERS file which associates the name and e-mail of Buildroot contributors/developers with the packages they take care of. So, what Victor did is:

  • Extend the pkg-stats script, which generates the statistics page, to not only generate a HTML output, but also a JSON output. A JSON output is obviously a lot more usable by other tools. Victor also improved the efficiency of this script in several ways, especially by parallelizing the requests made to
  • Extend the daily-mail script, which until now was only sending autobuild results, to also send notifications about packages that are not up to date with their latest upstream version

The notifications are sent only once a week, both individually to the developers, and globally on the mailing list. They are grouped in a single e-mail with the existing autobuild results notifications, to minimize the amount of e-mails received by developers. You can see an example of such a notification in this e-mail, with a small excerpt below:

Packages having a newer version

             name              | found by |        link to        |   version    |   upstream   | orph?
                           4th |  DISTRO  | | 3.62.5       | 3625         |     
                        acpica |  DISTRO  | | 20190703     | 20190816     |     
                         acpid |  DISTRO  | | 2.0.30       | 2.0.32       | ORPH
                       acsccid |  DISTRO  | | 1.1.4        | 1.1.7        |     
            adwaita-icon-theme |  DISTRO  | | 3.22.0       | 3.33.92      |     
                       aespipe |  GUESS   | | 2.4d         | 2.4e         | ORPH
                 android-tools |  GUESS   | | 4.2.2+git... | 10.0.0_r2    |     
                      argparse |  GUESS   | | 0.7.0-1      | 1.0.10       |     
                         argus |  GUESS   | | 3.0.8        |      | ORPH
                     armadillo |  GUESS   | | 7.900.1      | 9.700.2      |     
                   at-spi2-atk |  GUESS   | | 2.26.2       | 2.33.92      |     
                  at-spi2-core |  GUESS   | | 2.28.0       | 2.33.92      |     
                         atkmm |  GUESS   | | 2.24.2       | 2.29.1       |     
                      automake |  DISTRO  | | 1.15.1       | 1.16.1       | ORPH

As part of this work, Victor also improved the matching of versions between the Buildroot package versions and the upstream versions. Indeed, for many packages, Buildroot used to use the full Git tag name as the version (for example v1.3), while removes any prefix and keeps only 1.3.

As of today, not all Buildroot packages match with a project known by, either because doesn’t know the project, or because the name is slightly different, but we are improving this progressively (the name mismatch can be handled by creating a mapping on, thanks to the concept of distribution they have).

The work of Victor has already proven to be very useful: a number of infrequent contributors suddenly started taking care of the packages they had contributed a long time ago and perhaps forgotten since then, which is very good.

Notifications of defconfig and runtime test failures

Buildroot provides a number of defconfig files, which are example Buildroot configuration for a wide range of hardware platforms (Raspberry Pi, BeagleBone, Qemu emulated machines, NXP or Microchip evaluation boards, and more). These defconfigs offers a very simple way for users to get a minimal Buildroot system up and running on those hardware platforms, making them a great starting point. Of course, to make them useful, they have to build properly, and we regularly build them using Gitlab CI to ensure they continue to build.

Buildroot also has runtime tests, which were initially introduced in the project by your author back in 2017. Those runtime tests are test cases that will each build a specific well-defined Buildroot configuration, boot it under Qemu, and verify that everything works properly. For example, the filesystem test cases will each make a Buildroot build with a specific filesystem image format selected, and boot the result under Qemu, to make sure that the filesystem image is correct and working. We also have a significant number of test cases for Perl or Python modules, which simply build the Perl or Python interpreter with a collection of modules, boot under Qemu, and verify that those modules can be loaded/imported. Just like the defconfigs, these runtime tests are already tested on a regular basis using Gitlab CI, to detect and fix any regression.

However, the results of those tests in Gitlab CI (and especially failures) were not notified to the Buildroot community in a meaningful way. This is where Victor filled in the gap, by adding the appropriate notifications.

He further extended the daily-mail script so that using the Gitlab CI API, the latest Gitlab CI pipelines for the Buildroot project are retrieved, the defconfig and runtime test failures are identified, and the appropriate Buildroot developers and contributors are notified. Indeed, just like packages are referenced in Buildroot’s DEVELOPERS file, the defconfigs and runtime tests are also referenced. The daily-mail script will notify individual developers about the defconfig and runtime tests they take care of, and it will also globally notify the mailing list about all defconfig and runtime test failures.

An example output, visible in this notification e-mail is:

Detail of defconfig failures

                        defconfig |                        link to the job                        | orph?
                amarula_a64_relic |  |      
               arcturus_ucls1012a |  |      
                        bananapro |  |      
                   beaglebone_qt5 |  | ORPH 
        engicam_imx6qdl_icore_qt5 |  |      
                 imx6-sabresd_qt5 |  |      
                       imx6ulpico |  |      
                        imx7dpico |  |      
                    licheepi_zero |  |      
               linksprite_pcduino |  |      
                    orangepi_lite |  |      
                   orangepi_lite2 |  |      
                 orangepi_pc_plus |  |      
                    orangepi_zero |  |      
              orangepi_zero_plus2 |  |      
                   pc_x86_64_bios |  |      
                    pc_x86_64_efi |  |      
               raspberrypi3_qt5we |  | ORPH 
                            warp7 |  |      
                        warpboard |  | ORPH 

Detail of runtime-test failures

             runtime-test |                        link to the job                        | orph?
...ystemSystemdRoIfupdown |  | ORPH 
...ystemSystemdRoNetworkd |  | ORPH 
...nitSystemSystemdRwFull |  | ORPH 
...ystemSystemdRwIfupdown |  | ORPH 
...ystemSystemdRwNetworkd |  | ORPH 
             TestSyslogNg |  | ORPH 

Overall, thanks to Victor’s work, a single e-mail now reports autobuilder failures, the need to update packages to a newer upstream versions, defconfig build failures and runtime tests failures. This is a really good improvement in the tooling of the Buildroot community!

Buildroot autobuilder search capabilities

Buildroot provides over 2400 packages, and many of them have configurable features and optional dependencies. This creates a massive amount of possible configuration combinations, making it impossible to test all of them. To make sure as many Buildroot configurations build properly, the project has been running for many years the Buildroot autobuilders. A number of build machines build random Buildroot configurations 24/7, and report their results to This helps tremendously the Buildroot developers and maintainers to detect the problematic packages and configurations.

For a long time, the allowed to filter build results by architecture, C library, failing package, and a few other criterias. Such filtering is very often useful to understand when a package started failing to build, and in which situations it fails to build. was also collecting in a database all the configuration symbols (the BR2_something symbols) for every Buildroot configuration that was built. However, the size of this database made any query excessively long, so we were not able to make use of it so far. This was annoying because it would sometimes be useful to ask could you tell me which configuration had BR2_PACKAGE_STRACE=y and built successfully ?.

That’s where Victor jumped in:

  • He improved the database by adding the appropriate indexes and found a reasonably efficient way to query the database when configuration symbols are involved
  • He added filtering per configuration symbol, which can be done using GET arguments on the main page:[BR2_PACKAGE_STRACE]=y will show the builds that had BR2_PACKAGE_STRACE=y and that ended successfully. Multiple symbols[name]=value arguments can be passed.
  • Since writing such queries by hand was a bit cumbersome, Victor also added a new search page.
Autobuild search page
Autobuild search page

This work will be very useful in the future to analyze build failures and understand better in which situations they are happening.


Victor’s internship has been very productive in improving the tooling used by the Buildroot community to maintain the project. All the work done by Victor has been merged, is in production, and is already showing some useful results.

Building a Linux system for the STM32MP1: setting up a Qt5 application development environment

After showing how to build a minimal Linux system for the STM32MP157 platform, how to connect and use an I2C based pressure/temperature/humidity sensor and how to integrate Qt5 in our system, in this blog post, we are going to see how to set up a development environment to write our own Qt5 application, with QtCreator.

List of articles in this series:

  1. Building a Linux system for the STM32MP1: basic system
  2. Building a Linux system for the STM32MP1: connecting an I2C sensor
  3. Building a Linux system for the STM32MP1: enabling Qt5 for graphical applications
  4. Building a Linux system for the STM32MP1: setting up a Qt5 application development environment
  5. Building a Linux system for the STM32MP1: developing a Qt5 graphical application
  6. Building a Linux system for the STM32MP1: implementing factory flashing
  7. Building a Linux system for the STM32MP1: remote firmware updates

A minimal Qt5 application

We’ll call our application qt-sensor-demo, so create a directory with this name, outside of Buildroot. It’s important to not mix up your application code with your build system: you could very well decide to use another build system one day, while keeping your application code. To keep things simple, create this qt-sensor-demo side-by-side with Buildroot, as this will be important for a future step in this blog post.

In this directory, create a main.cpp file with the following code:

#include <QApplication>
#include <QPushButton>

int main(int argc, char* argv[])
    QApplication app(argc, argv);
    QPushButton hello("Hello world!");
    return app.exec();

It should be fairly straight-forward to understand that this program creates a QApplication object, a push button with the Hello world! label, sets the button size to 100 by 30 pixels, shows the button, and enters the application event loop. It is obviously a very basic application, because it doesn’t do anything useful, but that’s good enough as a starting point.

Now, we need to build this application. Building Qt applications by hand is definitely not reasonable, as Qt may need to run several tools on the source code before it gets built, and requires a number of compiler and linker flags. So, we won’t write a Makefile by hand, but instead use a build tool that generates the Makefile for us. We have a number of options here:

In this blog post, we’ll simply stick to qmake, which is good enough for a number of Qt-based applications. qmake takes as input one or several .pro files describing the project, and uses that to generate Makefiles (on Linux systems).

In our case, the file will be as simple as:

QT += widgets
SOURCES = main.cpp

Building our application

We have two ways to build our application:

  1. Manually outside of Buildroot. In this case, we’ll use the Buildroot-provided compiler and tools, but we will trigger the build of our application separately from the Buildroot build.
  2. Using Buildroot. In this case, our application would have a corresponding Buildroot package, that would automate building the application as part of the complete system build process.

Ultimately, we definitely want to have a Buildroot package for our application, to make sure the entire build is fully automated. However, during the active development of the application, it may be useful to build it manually outside of Buildroot, so we are going to see both solutions, which are not mutually exclusive: you can have a Buildroot package for your application, and still build it manually when you’re doing active development/debugging.

Building manually outside of Buildroot

To build manually, we simply need to first invoke Buildroot’s provided qmake:


This will generate a Makefile, that we can use to build our application:


At this point, you should have:

$ ls
main.cpp  main.o  Makefile  qt-sensor-demo

The qt-sensor-demo executable is compiled for ARM, and linked against the various libraries built by Buildroot.

Now, we need this executable on our STM32MP15 target. For now, we’ll simply add it to the SD card image:

cp qt-sensor-demo /path/to/buildroot/output/target/usr/bin/
cd /path/to/buildroot/

Hello World Qt application running on the STM32MP15 Discovery platform
Hello World Qt application running on the STM32MP15 Discovery platform
This will copy the executable to the output/target folder, which contains the root filesystem produced by Buildroot. Then invoking Buildroot’s make will ensure that the root filesystem and SD card images get re-generated. Of course, beware that if you run a Buildroot make clean, all the contents of output/, including output/target/ get removed. So this technique is only suitable for temporary changes. This is fine since anyway as discussed above, ultimately we’ll have a proper Buildroot package to build our qt-sensor-demo application.

Reflash your SD card with the new image, and on the target, run the demo:

# qt-sensor-demo -platform linuxfb

Setting SSH for communication with the board

Regenerating the SD card image and reflashing the entire SD card every time we want to change our application is not going to be very efficient during the application development/debugging. So instead, we’ll set up networking communication with the board, and use SSH to transfer files. This will also be useful for Qt Creator, as it uses SFTP to deploy files to the target.

Let’s start by enabling a small SSH client/server, called Dropbear. Go in Buildroot menuconfig, and enable the BR2_PACKAGE_DROPBEAR option (in Target packages, Networking applications, dropbear). While Dropbear provides SSH access, it does not support SFTP which will be needed by Qt Creator, so we’ll also enable an SFTP server, gesftpserver. So, we’ll enable BR2_PACKAGE_GESFTPSERVER as well (in Target packages, Networking applications, gesftpserver).

Then, in order to log in through SSH as root, we must have a non-empty root password, so set BR2_TARGET_GENERIC_ROOT_PASSWD (in System configuration, Root password) to a value you like.

You can now exit menuconfig, as we have enabled all features we needed. Before restarting the build, we need to do one last thing: set up a network configuration file so that our STM32MP15 system configures an IP address. To do this, we’ll create a /etc/network/interfaces file, and add it to the root filesystem using the root filesystem overlay mechanism, which was presented in the first post of this series. So, in your Buildroot sources, just create a file board/stmicroelectronics/stm32mp157-dk/overlay/etc/network/interfaces, with the following contents:

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static

This will ensure the eth0 interface of our target gets configured with the IP address. Of course, feel free to use a different IP address.

Then, run make in Buildroot, reflash your SD card, and boot your system. At boot time, you should see:

Starting dropbear sshd: OK

You can also run ip addr show dev eth0 to check the IP address of the eth0 interface:

2: eth0:  mtu 1500 qdisc mq qlen 1000
    link/ether 00:80:e1:42:4d:e3 brd ff:ff:ff:ff:ff:ff
    inet scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::280:e1ff:fe42:4de3/64 scope link 
       valid_lft forever preferred_lft forever

So the IPv4 address is properly set to, as expected.

Now, on your workstation, we need to configure the static IP address so that you can connect to your board. It is very likely that the Linux system on your workstation is using NetworkManager. Let’s add a connection:

$ nmcli con add con-name buildroot-target type ethernet ifname enp57s0u1u3 ip4
Connection 'buildroot-target' (234e0d9a-5c4f-4eac-9277-c3587bbd370d) successfully added.

Make sure to replace enp57s0u1u by the name of your PC wired interface, to which the board is connected. We of course assume you have an Ethernet cable directly connecting your PC to the board.

Finally, enable the connection:

$ nmcli con up id buildroot-target
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/10)

We can now ping our target:

$ ping
PING ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=64 time=1.33 ms

Log-in over SSH:

$ ssh root@
root@'s password: 
# uname -a
Linux buildroot 4.19.26 #1 SMP PREEMPT Wed Aug 28 15:54:58 CEST 2019 armv7l GNU/Linux
# cat /etc/issue 
Welcome to Buildroot

And verify that SFTP is working:

$ sftp root@
root@'s password: 
Connected to root@
sftp> ls /
/bin            /boot           /dev            /etc            
/lib            /lib32          /linuxrc        /lost+found     
/media          /mnt            /opt            /proc           
/root           /run            /sbin           /sys            
/tmp            /usr            /var            

So, now we can make a change to our Qt5 application, for example changing the label of the button, recompile by running make in the application directory, and directly copy the application using scp, and run it over ssh:

$ make
$ scp qt-sensor-demo root@
root@'s password: 
qt-sensor-demo                                    100%   12KB 634.7KB/s   00:00
$ ssh root@
root@'s password: 
# qt-sensor-demo -platform linuxfb

Much nicer, we don’t have to reflash our SD card every time we want to test a change in our application!

Note that we could create a public/private key pair, with the public key on our target, and this way not have to enter our password every time we want to transfer a file or log-in to the target. Since this blog post is already very long, we’ll live that as an exercise for the reader, there are plenty of resources on the Web about this topic.

Setting up Qt Creator

Some people (such as your author) are happy with using a powerful text editor (such as Vim or Emacs) and a terminal to do their application development. But others are sometimes more comfortable with an integrated development environment (IDE). So in this section, we’ll see how to set up Qt Creator to write, build, deploy and debug a Qt5 application.

Installing Qt Creator

First of all, you’ll have to install Qt Creator, which you can do using the package management system of your distribution. On Fedora systems, this would be:

$ sudo dnf install qt-creator

On Debian/Ubuntu systems:

$ sudo apt install qtcreator

The following instructions have been written and tested against Qt Creator version 4.9.2.

Creating a kit

After starting Qt Creator, the first thing to do is to create a kit, which describes the cross-compiler and Qt installation provided by Buildroot. Go to Tools -> Options, and the first item should be Kits:

Click on Add, and fill in the different fields as follows:

  • Name: Buildroot ARM
  • Device type: Generic Linux Device
  • Sysroot: /path/to/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/. Of course, replace /path/to/buildroot/ with the appropriate path on your system.
  • For the compiler, click on Manage, then in the Compiler panel:
    • Add one GCC C compiler, with the name Buildroot GCC and pointing to /path/to/buildroot/output/host/bin/arm-linux-gnueabihf-gcc
    • Add one GCC C++ compiler, with the name Buildroot G++ and pointing to /path/to/buildroot/output/host/bin/arm-linux-gnueabihf-g++
  • Back in the Kits panel, select Buildroot GCC and Buildroot G++ as the C and C++ compilers, respectively.
  • For the debugger, click on Manage, then in the debugger panel add one debugger named Buildroot GDB, and pointing to /path/to/buildroot/output/host/bin/arm-linux-gnueabihf-gdb. Back in the Kits panel, select Buildroot GDB as our debugger.
  • For the Qt version, click on Manage, then on Add, and point to the qmake binary in /path/to/buildroot/output/host/bin/. It will auto-detect that Buildroot has built Qt 5.11.3. You may want to adjust the version name from Qt %{Qt:Version} (host) to Qt %{Qt:Version} (Buildroot), as this Qt version is clearly not built for our host PC. Then back in the Kits panel, select this new Qt version.
  • For the Qt mkspec, enter devices/linux-buildroot-g++, which is the name of the mkspec configuration Buildroot generates.

You’ll find below screenshots of the various panels, with the details related to the Buildroot cross-compiler, cross-debugger and Qt installation:

Qt Creator Kits panel
Qt Creator Kits panel, filled in with the details of the Buildroot cross-compiler, cross-debugger and Qt installation
Qt Creator compiler panel, C compiler
Qt Creator compiler panel, filled in with the details of the Buildroot C compiler
Qt Creatoer compiler panel, C++ compiler
Qt Creator compiler panel, filled in with the details of the Buildroot C++ compiler
Qt Creator debugger panel
Qt Creator debugger panel, filled in with the details of the Buildroot cross-debugger
Qt Creator Qt version panel
Qt Creator Qt version panel, filled in with the details of the Buildroot Qt installation

We’re now done configuring a Kit!

Creating a device

In order to allow Qt Creator to deploy our application to the device, run it and debug it, we need to create a Device. Go again in Tools -> Options, and this time go to the Devices panel.

In the first window, select Generic Linux Device.

Qt Creator device creation, step 1

Then, for the device name, use STM32MP15 Discovery board for example, for the IP address, and for the user, root, which should give:

Qt Creator device creation, step 2

In the next step about Key deployment, simply skip to the next section, as we have not created a private/public key pair, as explained previously in this blog post. You can then finalize the device creation. Qt Creator will now test that it can communicate as expected with our device:

Qt Creator testing our new device

As you can see, it doesn’t find rsync on the target, because we have not installed it. It will use sftp instead, which is fine.

Back in the Device panel, you should see our device definition as follows:

Qt Creator device panel
Qt Creator device panel, filled in with the details of our STM32MP15 Discovery board

You can click on Open Remote Shell to directly open a shell over SSH to your target, or Show Running processes.

Our device is now set up correctly, time to create our first application!

Importing our project

We now want to import our qt-sensor-demo project in Qt Creator. To do so, go in File -> Open File or Project, then browse to the directory containing our qt-sensor-demo application, and select both the main.cpp and files, and click Open. Qt Creator should now switch to a Configure project window, where it asks you to select the Kit to use for this project. Obviously, select the Buildroot ARM kit we have just created, and validate by clicking Configure Project:

Qt Creator configure project

You should now see our project imported, with both of its files, and main.cpp is opened by default:

Qt Creator project

If we now use Build -> Build All, and then go in the Compile Output panel, we see:

13:11:58: Running steps for project qt-sensor-demo...
13:11:59: Starting: "/home/thomas/projets/outputs/st/host/bin/qmake" /home/thomas/qt-sensor-demo/ -spec devices/linux-buildroot-g++ CONFIG+=debug CONFIG+=qml_debug
Info: creating stash file /home/thomas/build-qt-sensor-demo-Buildroot_ARM-Debug/.qmake.stash
13:11:59: The process "/home/thomas/projets/outputs/st/host/bin/qmake" exited normally.
13:11:59: Starting: "/usr/bin/make" -f /home/thomas/build-qt-sensor-demo-Buildroot_ARM-Debug/Makefile qmake_all
make: Nothing to be done for 'qmake_all'.
13:11:59: The process "/usr/bin/make" exited normally.
13:11:59: Starting: "/usr/bin/make" -j4
/home/thomas/projets/outputs/st/host/bin/arm-linux-gnueabihf-g++ -c -pipe -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -Og --sysroot=/home/thomas/projets/outputs/st/host/arm-buildroot-linux-gnueabihf/sysroot -g -Wall -W -D_REENTRANT -fPIC -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../qt-sensor-demo -I. -I../projets/outputs/st/host/arm-buildroot-linux-gnueabihf/sysroot/usr/include/qt5 -I../projets/outputs/st/host/arm-buildroot-linux-gnueabihf/sysroot/usr/include/qt5/QtWidgets -I../projets/outputs/st/host/arm-buildroot-linux-gnueabihf/sysroot/usr/include/qt5/QtGui -I../projets/outputs/st/host/arm-buildroot-linux-gnueabihf/sysroot/usr/include/qt5/QtCore -I. -I../projets/outputs/st/host/mkspecs/devices/linux-buildroot-g++ -o main.o ../qt-sensor-demo/main.cpp
/home/thomas/projets/outputs/st/host/bin/arm-linux-gnueabihf-g++ --sysroot=/home/thomas/projets/outputs/st/host/arm-buildroot-linux-gnueabihf/sysroot -o qt-sensor-demo main.o   -lQt5Widgets -lQt5Gui -lQt5Core -lrt -ldl -latomic -lpthread 
13:12:00: The process "/usr/bin/make" exited normally.
13:12:00: Elapsed time: 00:02.

So we see that it is invoking qmake from Buildroot, and then running make, which builds our application, with the appropriate cross-compiler provided by Buildroot!

The application has been built in /home/thomas/build-qt-sensor-demo-Buildroot_ARM-Debug, which contains:

-rw-rw-r-- 1 thomas thomas 620760 30 août  13:12 main.o
-rw-rw-r-- 1 thomas thomas  31522 30 août  13:11 Makefile
-rwxrwxr-x 1 thomas thomas 516504 30 août  13:12 qt-sensor-demo

Running the application on the target

In order for Qt to deploy our application on the target, we need to adjust our .pro file so that it has directives to install the application. We’ll simply make our .pro file look like this:

QT += widgets
SOURCES = main.cpp
INSTALLS += target
target.path = /usr/bin

We invite you to read the relevant part of the Qt documentation to get details about the INSTALLS directive and the special target keyword.

Before we can really deploy on your target, we need to adjust the Run configuration, so click on the Project icon in the left bar, which should bring you to:

Qt Creator project build settings

We’re seeing the Build settings, so click on Run to see the Run settings. Everything should already be auto-detected: we want to deploy qt-sensor-demo to /usr/bin on the target, the target is STM32MP15 Discovery board. The only thing we need to change is to set Command line arguments to -platform linuxfb. Your settings should then look like this:

Qt Creator run settings

Now, you can finally do Build -> Run. Qt Creator will prompt you for the root password of your target, and automatically deploy and run the application!

Just to test it, make a change to the QPushButton label, and do Build -> Run again. You’ll see the new version of your application running!

Debugging your application

The last part in setting up our development environment is to be able to debug our application from Qt Creator. This involves remote debugging, where the debugger runs on your workstation, while the program being debugged runs on a separate target. As part of the Kit definition done previously, we have already told Qt Creator where the cross debugger provided by Buildroot is.

Now, we need to have gdbserver on the target, which is the program with which the cross-debugger will communicate to control the execution of our application on the target. To achieve this, go to the Buildroot menuconfig, and enable the option BR2_TOOLCHAIN_EXTERNAL_GDB_SERVER_COPY, in Toolchain -> Copy gdb server to the Target. With this done, we now need to have Buildroot take this change into account. Unfortunately simply running make will not take this change into account (see here for more details). We could do a full clean rebuild of Buildroot (make clean all), but that would take quite some time, so we’ll ask Buildroot to only reinstall the toolchain package and regenerate the root filesystem image:

make toolchain-external-arm-arm-reinstall all

Reflash your SD card, and reboot the system. You should now have gdbserver available on the target:

# ls -l /usr/bin/gdbserver 
-rwxr-xr-x    1 root     root        355924 Aug 29  2019 /usr/bin/gdbserver

We’ll now change a bit our program with some additional dummy code to play around with the debugger:

#include <QApplication>
#include <QPushButton>

int main(int argc, char* argv[])
    int a = 42;
    QApplication app(argc, argv);
    QPushButton hello("Hello world!");
    qDebug("Test 1");
    qDebug("Test 2");
    return app.exec();

Place a breakpoint on the line QApplication app(argc, argv) by clicking to the left of this line, it should show a red dot, like this:

Qt Creator breakpoint

Then you can start debugging by clicking on the following button in the left bar:

Qt Creator debug button

It will switch to the debug view, with the program stopped at our breakpoint:

Qt Creator debug view

At the bottom of the screen, click on Application Output so that we can see the stdout of the application running on the target. Now hit F10 to step through our code line by line. You should then see the value of the variable a updated in the top right panel, and the Test 1 and then Test 2 messages printed in the application output:

Qt Creator debugging

So, as expected, we are able to debug our application! This concludes the setup of Qt Creator, which allows us to very easily make a change to our application, build it, deploy it on the target and debug it.

Building using a Buildroot package

Before we conclude this article, we want to see how to integrate the build of our application with Buildroot. Indeed, building the application manually or through Qt Creator is perfectly fine during the active development of the application. But in the end, we want Buildroot to be able to build our complete system, including all the applications and libraries we have developed, in a fully automated and reproducible fashion.

To achieve this, in this section, we’ll create a Buildroot package for our qt-sensor-demo application. A package in Buildroot speak is a small set of metadata that tells Buildroot how to retrieve and build a particular piece of software.

To learn how to create a Buildroot package, we suggest you to read the relevant section of the Buildroot manual, or to read the slides of our Buildroot training course. The following steps will however guide you in the process of creating our qt-sensor-demo package.

First, in the Buildroot source tree, create a package/qt-sensor-demo/ directory. Then, create a file named package/qt-sensor-demo/, which describes one configuration option to be able to enable/disable this package from Buildroot’s menuconfig:

        bool "qt-sensor-demo"
        depends on BR2_PACKAGE_QT5
          This is the qt-sensor-demo application.

Note that the bool, depends on, select and help keywords need to be prefixed with a tab (not spaces), and that the BR2_PACKAGE_QT_SENSOR_DEMO string should be exactly as-is, as it needs to match the name of the directory qt-sensor-demo.

This file basically creates a boolean option which will appear as qt-sensor-demo in menuconfig. The depends on BR2_PACKAGE_QT5 definition ensures that our option will only be selectable if Qt5 is available, while select BR2_PACKAGE_QT5BASE_WIDGETS makes sure Qt5 will be built with QtWidgets support, as we use them.

Now, edit the existing package/ file, and at a relevant place (perhaps Graphic libraries and applications, submenu Graphic applications), you need to add:

source "package/qt-sensor-demo/"

So that Buildroot’s menuconfig properly includes and reads our new package file. Now, if you run make menuconfig in Buildroot, you should be able to see our new option and enable it. Of course for now, it doesn’t do anything useful.

The next step is to create a file in package/qt-sensor-demo/ to teach Buildroot how to build our package. This .mk file is a Makefile, which uses a number of Buildroot-specific variables and macros, to a point where it doesn’t really look like a typical Makefile. In our case, will look like this:

# qt-sensor-demo

QT_SENSOR_DEMO_SITE = $(TOPDIR)/../qt-sensor-demo


	(cd $(@D); $(QT5_QMAKE))


	$(INSTALL) -D -m 0755 $(@D)/qt-sensor-demo $(TARGET_DIR)/usr/bin/qt-sensor-demo


$(eval $(generic-package))

The first two variables, QT_SENSOR_DEMO_SITE and QT_SENSOR_DEMO_SITE_METHOD tell Buildroot how to retrieve the source code for this application. Most Buildroot packages retrieve tarballs of source from HTTP servers, or clone source code from Git repositories. But in the case of our package, we are simply taking the source from the qt-sensor-demo directory, located just one level up from the main Buildroot source directory.

The QT_SENSOR_DEMO_DEPENDENCIES variable tells Buildroot that the qt5base package needs to be built before qt-sensor-demo gets built.

The QT_SENSOR_DEMO_CONFIGURE_CMDS variable describes the commands to run to configure our package. Here, we simply call Qt’s qmake utility, using the Buildroot-provided variable QT5_QMAKE.

The QT_SENSOR_DEMO_BUILD_CMDS variable describes the commands to run to build our package. In our case, we invoke make in the application directory, $(@D), passing appropriate variables in the environment ($(TARGET_MAKE_ENV)).

Then, the QT_SENSOR_DEMO_INSTALL_TARGET_CMDS variable describes the commands to run to install our package. We simply copy the qt-sensor-demo executable from the build directory ($(@D)) to usr/bin in the target directory.

Finally, the generic-package macro invocation is what triggers the Buildroot machinery to create a package. Read the Buildroot manual and/or our Buildroot training slides for more details.

With this in place, if you have already enabled qt-sensor-demo in menuconfig, when you run make in Buildroot, you should see:

>>> qt-sensor-demo  Syncing from source dir /home/thomas/qt-sensor-demo
rsync -au --chmod=u=rwX,go=rX --exclude .svn --exclude .git --exclude .hg --exclude .bzr --exclude CVS  /home/thomas/qt-sensor-demo/ /home/thomas/buildroot/output/build/qt-sensor-demo
>>> qt-sensor-demo  Configuring
(cd /home/thomas/buildroot/output/build/qt-sensor-demo; /home/thomas/buildroot/output/host/bin/qmake -spec devices/linux-buildroot-g++)
>>> qt-sensor-demo  Building
PATH="..." /usr/bin/make -j5 -C /home/thomas/buildroot/output/build/qt-sensor-demo
/home/thomas/buildroot/output/host/bin/arm-linux-gnueabihf-g++ --sysroot=/home/thomas/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot -Wl,-O1 -o qt-sensor-demo main.o   -L/home/thomas/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib -lQt5Widgets -lQt5Gui -lQt5Core -lrt -ldl -latomic -lpthread 
>>> qt-sensor-demo  Installing to target
/usr/bin/install -D -m 0755 /home/thomas/buildroot/output/build/qt-sensor-demo/qt-sensor-demo /home/thomas/buildroot/output/target/usr/bin/qt-sensor-demo

You’re seeing:

  1. Buildroot copying the source code from its original location to the Buildroot build directory
  2. Buildroot configuring the build of our package by invoking qmake
  3. Buildroot building our application
  4. Buildroot installing our application

The application being installed in Buildroot’s target directory, it is automatically part of the root filesystem image, and consequently the SD card image sdcard.img. You can flash it again, and see that you have the same application.

Now, if you want to change the source code of your application, you can simply change it in its original location, the qt-sensor-demo directory, and issue the following command in Buildroot:

$ make qt-sensor-demo-rebuild all

Buildroot will synchronize again the source code from its original directory to Buildroot’s build directory, and rebuild the application. It will only transfer the files that have changed, and only rebuild the files that have changed. The all target ensures that the root filesystem and SD card images get regenerated with the new version of the code.


In this article, we’ve seen many things:

  • How to create and manually build our first Qt5 application
  • How to deploy our application to the target by adding it to the SD card
  • How to set up network communication, and SSH, to deploy our application more efficiently during development
  • How to set up Qt Creator as a development environment to write, build, deploy and debug our application
  • How to create a Buildroot package to automate the build of our application

You can find the Buildroot changes corresponding to this blog post in the 2019.02/stm32mp157-dk-blog-4 branch of our repository. The qt-sensor-demo application code can be found in the blog-4 branch of this application Git repository.

In our next blog post, we’ll extend our qt-sensor-demo application to make it really useful!