Raspberry pi cannot read from GPIO using pi4J

Question

I am running the code at the bottom using java and Pi4j library, pretty much the program checks is the pin is low and waits sometime before turning off the tv.

When I reboot my Raspberry and run the code, I get no issues. however when I close the program using CTR+C and run again, sometimes I get the this error when I start the program, and I cannot read from the sensor :

wiringPiSetup: mmap failed: No such file or directory

and also the following error

file:/opt/jdk1.8.0/jre/lib/ext/jfxrt-controls.jar!/com/sun/javafx/scene/control/skin/modena/modena.bss
Exception in thread "Thread-5" java.lang.NullPointerException
at javafxapplication4.JavaFXApplication4.lambda$0(JavaFXApplication4.java:672)
at javafxapplication4.JavaFXApplication4$$Lambda$3.run(Unknown Source)
at java.lang.Thread.run(Thread.java:724)

and my code is

 new Thread(() -> {
            final GpioController gpioSensor = GpioFactory.getInstance();
            sensor_lastTimerCall = System.currentTimeMillis();
            final GpioPinDigitalInput sensor = gpioSensor.provisionDigitalInputPin(RaspiPin.GPIO_02, PinPullResistance.PULL_DOWN);
            sensor.addListener(new GpioPinListenerDigital() {
                @Override
                public void handleGpioPinDigitalStateChangeEvent(GpioPinDigitalStateChangeEvent event) {
                    if (event.getState().isHigh()) {
                        sensor_lastTimerCall = System.currentTimeMillis();
                        ProcessBuilder processBuilder1 = new ProcessBuilder("bash", "-c", "echo \"as\" | cec-client -d 1 -s \"standby 0\" RPI");
                        try {
                            Process process1 = processBuilder1.start();
                        }catch (IOException ex) {
                            Logger.getLogger(JavaFXApplication4.class.getName()).log(Level.SEVERE, null, ex);
                        }   
                    }
                    if(event.getState().isLow()){sensorLow = true;}
                }
            });
            System.out.println(" ... Motion Detection Starting.....");

            for (;;) {
                try {
                    Thread.sleep(1000);
                    long now = System.currentTimeMillis();
                    if (System.currentTimeMillis() > sensor_lastTimerCall + 360000 && sensorLow) {
                        System.out.println("All is quiet...");
                        ProcessBuilder processBuilder2 = new ProcessBuilder("bash", "-c", "echo \"standby 0000\" | cec-client -d 1 -s \"standby 0\" RPI");
                        try {
                            Process process2 = processBuilder2.start();
                        }catch (IOException ex) {
                            Logger.getLogger(JavaFXApplication4.class.getName()).log(Level.SEVERE, null, ex);
                        }
                        sensor_lastTimerCall = now;
                        sensorLow = false;
                    }
                } catch(InterruptedException ex) {
                    gpioSensor.shutdown();
                    Thread.currentThread().interrupt();
                }
            }

        }).start();

    }

any idea how to fix this?

Answer 1

I get the same problem but only when I shutdown and restart the program right away. I put a one second delay before getting the gpio instance. You can check for null and try again as needed, but it hasn't failed since.

    // create gpio controller
    log("trying to get gpio controller... ");
    Thread.sleep(1000);
    final GpioController gpio = GpioFactory.getInstance();
    if (gpio != null)
        log("opened gpio controller");
    else {
        //try again later if you want 
        log("failed to get gpio controller");
        System.exit(1);
    }

Answer 2

1.- you can check u have pi4j correct installed into the project 2.- try to use PinPullResistance.PULL_UP 3.- comment all other code but what u need to check if pin is working, so you can check if that pin is working as expected. 4.- i can give u an example for me is workin:

//SETUP gpio = GpioFactory.getInstance( ); GpioPinDigitalInput rigthPad; //gpio 23 rigthPad = gpio.provisionDigitalInputPin( RaspiPin.GPIO_23, PinPullResistance.PULL_UP );

//add listener like u have above //finally implement GpioPinListenerDigital

i dont recall if you have to change the configuration first