Android Things - Gpio.getValue() always returning true

Question

I have trying to set and get gpio value on Android Things, I am using raspberry pi 3 and have my connections at BCM26(output), BCM16(input).

I have also tried changing the pins and checked them using DMM as well, no matter what I do I am unable to set the output high. and even getValue gpio also return false.

mMotorGpio = service.openGpio(MOTOR_PIN_NAME);
            mMotorGpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);

            Log.i(TAG, "Output GPIO set");

. . .

 try {
                boolean newVal = !mMotorGpio.getValue();

                Log.i(TAG,"setting port value as " + newVal);

                mMotorGpio.setValue(newVal);

            }catch (IOException e){
                e.printStackTrace();
            }

Answer 1

Seems like you are trying to read from the pin,which is configured for output:

mMotorGpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);

and also you didn't configured voltage signal to be returned as true (active), for example:

mMotorGpio.setActiveType(Gpio.ACTIVE_HIGH);

if you want high voltage as active as described in Official Documentation (section Reading from an input).

So,you will need 2 separate Gpio objects (one for Input, other for Output) to do, what you want. Something like this:

private static final String MOTOR_PIN_OUT_NAME = "BCM26";
private static final String MOTOR_PIN_IN_NAME = "BCM16";

private Gpio mMotorGpioIn;
private Gpio mMotorGpioOut;

...

mMotorGpioIn = service.openGpio(MOTOR_PIN_IN_NAME);
mMotorGpioIn.setDirection(Gpio.DIRECTION_IN);
mMotorGpioIn.setActiveType(Gpio.ACTIVE_HIGH);

mMotorGpioOut = service.openGpio(MOTOR_PIN_OUT_NAME);
mMotorGpioOut.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);
mMotorGpioOut.setActiveType(Gpio.ACTIVE_HIGH);

...

try {
    boolean newVal = !mMotorGpioIn.getValue();

    Log.i(TAG,"setting port value as " + newVal);

    mMotorGpioOut.setValue(newVal);

} catch (IOException e){
    e.printStackTrace();
}

Answer 2

You cannot reliably read the state value of a pin configured as an output. From the GPIO reference docs for getValue() :

Get the current value of the GPIO pin (for GPIO pins configured as input only). Returns an unpredictable value when the GPIO is configured as output.