检测树莓派-Qt5中的GPIO引脚更改

Question

I'm fairly new to the raspberry pi.

The essence of my problem is as follows:

I have a GPIO pin change that must be monitored(continuously polled) to see if it changes. If it changes, I must load a new QML file in my Qt5 project using a Loader. I know how to do the loader part, considering its fairly simple. I need a way to poll the GPIO pin and to be notified of a change.

I've read that the QSocketNotifier class maybe helpful. But I'm frankly clueless as to how to do this.

Any help provided towards figuring out how to do this is appreciated. Thank you :)

EDIT: I'm building a sort of a Main Menu to select different options on a GUI for a raspberry pi based system, running on Debian. It's roughly like a set top box. In equivalence to the GUI based buttons on screen, It should be able to acquire a hardware based interrupt from external buttons that are connected to the GPIO pins that causes a new page to load/a new activity to begin.

If I understand correctly, the c++ part of the code must capture this pin change, and relay it to the QML part. I need to be able to do this.

Answer 1

You said nothing about the environment and anything else that needs doing. If there are not other tasks nor an o/s, maybe something this is what you want?:

int last_state = -1;   // impossible state so change is noticed the first time
for (;;)  // do forever
{
       int state = get_gpio (THE_EVENT);
       if (state == last_state)
       {
            sleep (100);
            continue;
       }
       do_loader_stuff();
       last_state = state;
}

Answer 2

You can configure the pin to be interrupt driven. The way this works is that after you perform the configuration, you can now select() on the file representing the pin, and select() will return when the pin changes state.

Here is the documentation on the sysfs gpio interface: https://www.kernel.org/doc/Documentation/gpio/sysfs.txt

Here is what the setup for pin 19 would look like:

QFile exportFile("/sys/class/gpio/gpio19/export");
exportFile.open(QIODevice::WriteOnly);
exportFile.write("19");

QFile directionFile("/sys/class/gpio/gpio19/direction");
directionFile.open(QIODevice::WriteOnly);
directionFile.write("in");

QFile edgeFile("/sys/class/gpio/gpio19/edge");
edgeFile.open(QIODevice::WriteOnly);
edgeFile.write("body");

Now, instead of using select() directly, you can use QSocketNotifier .

QFile file("/sys/class/gpio/gpio19/value");

QSocketNotifier notifier(file.handle(), QSocketNotifier::Read);
connect(&notifier, &QSocketNotifier::activated, this, &MyClass::interruptFired);