How to Use GPIO

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GPIO resources can be accessed either using the GPIO Service provided by ESF, or directly using the OpenJDK Device I/O embedded library.

GPIO Service

Access to GPIO resources is granted by the GPIOService. Once retrieved, the service can be used to acquire a GPIO Pin and use it as a digital output or a digital input.

The GPIO Service exposes methods to retrieve a GPIO Pin via its name or index as shown below.

KuraGpioPin thePin = gpioServiceInstance.getPinByTerminal(18);

KuraGpioPin thePin = gpioServiceInstance.getPinByName("IgnitionPin");

The KuraGpioPin object is used to manipulate GPIO Pins and exposes methods to read the status of an input, or set the status of digital output as shown below.

//sets digital output value to high
thePin.setValue(true);

//get value of a digital input pin
boolean active = thePin.getValue();

//listen for status change on a digital input pin
try {
  thePin.addPinStatusListener(new PinStatusListener() {
    @Override
    public void pinStatusChange(boolean value) {
      // Perform tasks when pin status changes
    }
  });
} catch (KuraClosedDeviceException e) {
  // Here if GPIO cannot be acquired
} catch (IOException e) {
  // Here on I/O error
}

Pin Configuration

Pin names, indexes, and configuration are defined in the jdk.dio.properties file.

Although GPIO pins can be accessed with their default configuration, the settings of each pin can be changed when acquiring it with the GPIO Service as shown below.

KuraGpioPin customInputPin = gpioServiceInstance.getPinByTerminal(
  14, 
	KuraGPIODirection.INPUT, 
	KuraGPIOMode.INPUT_PULL_UP, 
	KuraGPIOTrigger.BOTH_LEVELS);

OpenJDK Device I/O

Linux-level access in ESF is granted through OpenJDK Device I/O, a third-party library that leverages standard Java ME Device I/O APIs to Java SE. ESF is distributed with the relevant native libraries, together with the default hardware configuration, for each platform on which it runs.

I2C, SPI, and GPIO resources can be directly accessed through the jdk.dio library present in the target platform.

Default Configuration

Default hardware configuration for the hardware platform is defined in the jdk.dio.properties file. Standard configuration for complex devices can be added on a per-device basis as shown below.

#Default PIN configuration. To be overwritten in the following lines
gpio.GPIOPin = initValue:0, deviceNumber:0, direction:3, mode:-1, trigger:3

#Standard PIN configuration
64 = deviceType: gpio.GPIOPin, pinNumber:64, name:RELAY1

APIs

ESF supports the full set of APIs for the listed device types. Refer to References for further API information.

Accessing a GPIO Pin with OpenJDK Device I/O

A GPIO Pin can be accessed by referencing its index in the properties file, or by creating a Pin configuration object and feeding it to the DeviceManager as shown in the code examples below.

Accessing a GPIO Pin by its Index

#Accessing the GPIO Pin number 17. The default behaviour is defined in the
#jdk.dio.properties file
#
#i.e.:
# gpio.GPIOPin = initValue:0, deviceNumber:0, direction:3, mode:-1, trigger:3
# 17 = deviceType: gpio.GPIOPin, pinNumber:17, name:GPIO_USER_1

GPIOPin led = (GPIOPin)DeviceManager.open(17);

led.setValue(true) //Turns the LED on
led.setValue(false) //Turns the LED off
boolean status = led.getValue() //true if the LED is on

Accessing a GPIO Pin Using a Device Configuration Object

#Accessing the Pin number 17 with custom configuration

GPIOPinConfig pinConfig = new GPIOPinConfig(
	DeviceConfig.DEFAULT, 						//GPIO Controller number or name
	17, 												//GPIO Pin number
	GPIOPinConfig.DIR_INPUT_ONLY,				//Pin direction
	GPIOPinConfig.MODE_INPUT_PULL_DOWN, 	//Pin resistor
	GPIOPinConfig.TRIGGER_BOTH_EDGES, 		//Triggers
	false 											//initial value (for outputs)
);

GPIOPin button = (GPIOPin) DeviceManager.open(GPIOPin.class, pinConfig);

button.setInputListener(new PinListener(){
		@Override
		public void valueChanged(PinEvent event) {
			System.out.println("PIN Status Changed!");
			System.out.println(event.getLastTimeStamp() + " - " + event.getValue());
		}
});

Updated about 5 years ago