Raspberry Pi GPIO with C/C++ using 3rd party library pigpio

[Dewiren]

Hello Everyone,

I have a problem with using 3rd party library pigpio.

The application works well, i saw gpio value via qDebug() in Application Output screen but i can't set ui widget values at aFunction().

When i used ui->cdNumber->display(RPM) in aFunction() i get error "invalid use of member ‘ui’ in static member function"

How do I fix this problem? or How should I go about solving this problem?

My qt Application:

I added .pro file at below code.

LIBS += -lpigpio -lrt -lpthread

Mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "QDebug"
#include <pigpio.h>
#include <QTimer>


namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

public slots:


private:
    Ui::MainWindow *ui;
    QTimer *ScreenRefreshing;


private slots:
    static void aFunction(int gpio, int level, uint32_t tick);

    void Screen_Refreshing();
};

#endif // MAINWINDOW_H

Mainwindow.cpp:

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    if (gpioInitialise() < 0)
    {
        qDebug() << "pigpio initialisation failed";
    }
    else
    {
        qDebug() << "pigpio initialised ok";
    }

    gpioSetMode(20, PI_INPUT);
    gpioSetPullUpDown(20, PI_PUD_OFF);
    gpioSetAlertFunc(20, aFunction);

    ScreenRefreshing = new QTimer(this);
    connect(ScreenRefreshing, SIGNAL(timeout()), this, SLOT(Screen_Refreshing()));
    ScreenRefreshing->start(100);

}

MainWindow::~MainWindow()
{
    gpioTerminate();
    delete ui;
}

void MainWindow::aFunction(int gpio, int level, uint32_t tick)
{
    double RPM = 0;

    if(gpio == 20)
    {
        if(level == 1)
        {
           static uint32_t lastTick = 0;

           if (lastTick)
           {

               qDebug() << "GPIO = " << gpio << "LEVEL = " << level << "Tick = " << tick;

               RPM = (double(tick - lastTick) / 1000000.0) * 3600;
               qDebug() << "RPM = " << RPM;

               // ui->lcdNumber_Distance->display(RPM);  // ->>>>>>>>> "invalid use of member ‘ui’ in static member function"

           }
           else
           {
               //qDebug() << "2. Level = " << level;
               //printf("%d 0.00\n", level);
           }

           lastTick = tick;
        }
    }
}

void MainWindow::Screen_Refreshing()
{
    // for test
}

The function I use and its description:

	
int gpioSetAlertFunc(unsigned user_gpio, gpioAlertFunc_t f)
Registers a function to be called (a callback) when the specified GPIO changes state.

user_gpio: 0-31
        f: the callback function


Returns 0 if OK, otherwise PI_BAD_USER_GPIO.

One callback may be registered per GPIO.

The callback is passed the GPIO, the new level, and the tick.

Parameter   Value    Meaning

GPIO        0-31     The GPIO which has changed state

level       0-2      0 = change to low (a falling edge)
                     1 = change to high (a rising edge)
                     2 = no level change (a watchdog timeout)

tick        32 bit   The number of microseconds since boot
                     WARNING: this wraps around from
                     4294967295 to 0 roughly every 72 minutes


The alert may be cancelled by passing NULL as the function.

The GPIO are sampled at a rate set when the library is started.

If a value isn't specifically set the default of 5 us is used.

The number of samples per second is given in the following table.

              samples
              per sec

         1  1,000,000
         2    500,000
sample   4    250,000
rate     5    200,000
(us)     8    125,000
        10    100,000


Level changes shorter than the sample rate may be missed.

The thread which calls the alert functions is triggered nominally 1000 times per second. The active alert functions will be called once per level change since the last time the thread was activated. i.e. The active alert functions will get all level changes but there will be a latency.

If you want to track the level of more than one GPIO do so by maintaining the state in the callback. Do not use gpioRead. Remember the event that triggered the callback may have happened several milliseconds before and the GPIO may have changed level many times since then.

The tick value is the time stamp of the sample in microseconds, see gpioTick for more details.

Example

void aFunction(int gpio, int level, uint32_t tick)
{
   printf("GPIO %d became %d at %d", gpio, level, tick);
}

// call aFunction whenever GPIO 4 changes state

gpioSetAlertFunc(4, aFunction);

Thanks in advance

[SGaist]

Hi and welcome to devnet,

That's because you try to access a standard member variable from a static function.

Take a look at the ir_receiver example of the pigpio project. It shows how to use a class with the callback with gpioSetAlertFuncEx.