Using MCE interface for LED activation in Maemo 5

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Created: divanov (09 Feb 2010)

Last edited: hamishwillee (11 Oct 2012)

N900 device has LED, which can be controlled from application. There is MCE interface for controlling LED through DBus. MCE LED interface D-Bus methods - online documentation.

One can use dbus-send command line utility to try those methods without code writing. dbus-send manual page - note, an example contains missing quote.

Let's make an application, which plays all predefined LED patterns in a loop. QTimer is used to activate LedExample's slot every 5 seconds.

#include <QApplication>
#include <QTimer>
 
#include "ledexample.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    LedExample ledExample;
 
    ledExample.show();
 
    QTimer timer;
    QObject::connect(&timer, SIGNAL(timeout()), &ledExample, SLOT(activate()));
    timer.start(5000);
 
    return a.exec();
}

This is how ledexample.h looks like.

#ifndef LED_EXAMPLE_H
#define LED_EXAMPLE_H
 
#include <QLabel>
#include <QStringList>
#include <QDBusInterface>
 
class LedExample : public QLabel
{
    Q_OBJECT
 
public:
    LedExample(QWidget *parent=0);
    ~LedExample();
 
public slots:
    void activate();
 
private:
    QDBusInterface *interface;
    QStringList patterns;
    int index;
};
 
#endif //LED_EXAMPLE_H

You can find list of predefined LED patterns in /etc/mce/mce.ini on the device. In constructor we fill string list with all those predefined patterns. MCE DBus interface is quite simple. In order to select currently active patter use MCE_ACTIVATE_LED_PATTERN and MCE_DEACTIVATE_LED_PATTERN with pattern name. We call those methods in activate() slot. And MCE_ENABLE_LED and MCE_DISABLE_LED switch LED actually on/off. We call those two methods in constructor and destructor respectively.

Implementation of LedExample:

#include <mce/dbus-names.h>
#include <QDBusMessage>
#include <QDebug>
 
#include "ledexample.h"
 
LedExample::LedExample(QWidget *parent)
    : QLabel(parent), index(-1)
{
    setAlignment(Qt::AlignCenter);
    setFont(QFont("Nokia Sans", 35, QFont::Bold));
 
    patterns << "PatternError" << "PatternDeviceOn" << "PatternPowerOn"
             << "PatternPowerOff" << "PatternCommunicationCall"
             << "PatternCommunicationIM" << "PatternCommunicationSMS"
             << "PatternCommunicationEmail" << "PatternCommonNotification"
             << "PatternWebcamActive" << "PatternBatteryCharging"
             << "PatternBatteryFull" << "PatternDeviceSoftOff";
 
    interface = new QDBusInterface(MCE_SERVICE, MCE_REQUEST_PATH,
                                   MCE_REQUEST_IF, QDBusConnection::systemBus(),
                                   this);
 
    QDBusMessage reply = interface->call(MCE_ENABLE_LED);
    if (reply.type() == QDBusMessage::ErrorMessage)
        qDebug() << reply.errorMessage();
}
 
 
LedExample::~LedExample()
{
    QDBusMessage reply;
 
    reply = interface->call(MCE_DISABLE_LED);
    if (reply.type() == QDBusMessage::ErrorMessage)
        qDebug() << reply.errorMessage();
 
    if (index > -1) {
        reply = interface->call(MCE_DEACTIVATE_LED_PATTERN, patterns.at(index));
        if (reply.type() == QDBusMessage::ErrorMessage)
            qDebug() << reply.errorMessage();
    }
}
 
 
void LedExample::activate()
{
    if (patterns.count() < 1)
        return;
 
    QDBusMessage reply;
 
    if (index > -1) {
        reply = interface->call(MCE_DEACTIVATE_LED_PATTERN, patterns.at(index));
        if (reply.type() == QDBusMessage::ErrorMessage)
            qDebug() << reply.errorMessage();
    }
 
    index = index < patterns.count() - 1 ? ++index : 0;
 
    setText(patterns.at(index));
 
    reply = interface->call(MCE_ACTIVATE_LED_PATTERN, patterns.at(index));
    if (reply.type() == QDBusMessage::ErrorMessage)
        qDebug() << reply.errorMessage();
}

Project file should be something like this:

TEMPLATE = app
TARGET = 
DEPENDPATH += .
INCLUDEPATH += .
 
QT += dbus
 
unix {
    CONFIG += link_pkgconfig
    PKGCONFIG += mce
}
 
# Input
HEADERS += ledexample.h
SOURCES += main.cpp \
           ledexample.cpp