Gpio

public interface Gpio
implements Closeable

com.google.android.things.pio.Gpio
Known Indirect Subclasses

Controls a GPIO pin.

General-purpose input/output (GPIO) pins are physical pins on an integrated circuit that can be controlled via software. A GPIO pin can be configured as input to read the voltage value or as output to change the voltage value. It only understands logic values (true/false) which maps physically to a low value (the pin has the same voltage as Ground) or high value (the pin has the same voltage as IOREF). GPIOs are frequently used to communicate with simple peripherals like sensors and actuators.

Opening a GPIO pin takes ownership of it for the whole system, preventing anyone else from opening/accessing the GPIO until you call close(). Forgetting to call close() will prevent anyone (including the same process/app) from using the GPIO.

Summary

Constants

int ACTIVE_HIGH

ActiveType constant to select active high, which means that logical true corresponds with high voltage.

int ACTIVE_LOW

ActiveType constant to select active low, which means that logical true corresponds with low voltage.

int DIRECTION_IN

Direction constant used to configure a GPIO pin as an input.

int DIRECTION_OUT_INITIALLY_HIGH

Direction constant used to configure a GPIO pin as an output and initialize its state to true (equivalent of calling setValue(true)).

int DIRECTION_OUT_INITIALLY_LOW

Direction constant used to configure a GPIO pin as an output and initialize its state to false (equivalent of calling setValue(false)).

int EDGE_BOTH

EdgeType constant used to configure the GPIO interrupt to trigger on any edge (when getValue() changes state in either direction).

int EDGE_FALLING

EdgeType constant used to configure the GPIO interrupt to trigger on falling edge (when getValue() goes from true to false).

int EDGE_NONE

EdgeType constant used to configure the GPIO interrupt to never trigger.

int EDGE_RISING

EdgeType constant used to configure the GPIO interrupt to trigger on rising edge (when getValue() goes from false to true).

Public methods

abstract void close()

Releases the GPIO pin.

default String getName()

Returns the I/O name.

abstract boolean getValue()

Gets the current value of the GPIO pin (for GPIO pins configured as input only).

default void registerGpioCallback(GpioCallback callback)

Registers a callback for GPIO edge interrupts.

abstract void registerGpioCallback(Handler handler, GpioCallback callback)

Registers a callback for GPIO edge interrupts.

abstract void setActiveType(int activeType)

Sets the active level.

abstract void setDirection(int direction)

Sets the direction of the GPIO pin.

abstract void setEdgeTriggerType(int edgeTriggerType)

Sets the interrupt trigger type.

abstract void setValue(boolean value)

Sets the value of the GPIO pin (for GPIO pins configured as output only).

abstract void unregisterGpioCallback(GpioCallback callback)

Unregisters an interrupt callback.

Inherited methods

From interface java.io.Closeable
From interface java.lang.AutoCloseable

Constants

ACTIVE_HIGH

int ACTIVE_HIGH

ActiveType constant to select active high, which means that logical true corresponds with high voltage.

Constant Value: 1 (0x00000001)

ACTIVE_LOW

int ACTIVE_LOW

ActiveType constant to select active low, which means that logical true corresponds with low voltage.

Constant Value: 0 (0x00000000)

DIRECTION_IN

int DIRECTION_IN

Direction constant used to configure a GPIO pin as an input.

Constant Value: 0 (0x00000000)

DIRECTION_OUT_INITIALLY_HIGH

int DIRECTION_OUT_INITIALLY_HIGH

Direction constant used to configure a GPIO pin as an output and initialize its state to true (equivalent of calling setValue(true)).

Constant Value: 1 (0x00000001)

DIRECTION_OUT_INITIALLY_LOW

int DIRECTION_OUT_INITIALLY_LOW

Direction constant used to configure a GPIO pin as an output and initialize its state to false (equivalent of calling setValue(false)).

Constant Value: 2 (0x00000002)

EDGE_BOTH

int EDGE_BOTH

EdgeType constant used to configure the GPIO interrupt to trigger on any edge (when getValue() changes state in either direction).

Constant Value: 3 (0x00000003)

EDGE_FALLING

int EDGE_FALLING

EdgeType constant used to configure the GPIO interrupt to trigger on falling edge (when getValue() goes from true to false).

Constant Value: 2 (0x00000002)

EDGE_NONE

int EDGE_NONE

EdgeType constant used to configure the GPIO interrupt to never trigger.

Constant Value: 0 (0x00000000)

EDGE_RISING

int EDGE_RISING

EdgeType constant used to configure the GPIO interrupt to trigger on rising edge (when getValue() goes from false to true).

Constant Value: 1 (0x00000001)

Public methods

close

void close ()

Releases the GPIO pin.

This must be called in order for the GPIO pin to be released and be available to other users. Closing a GPIO does not change its state, for example if it closed while outputting a high signal, it will continue to output high until another user opens it and changes its state.

Throws
IOException if the GPIO is already closed.

getName

String getName ()

Returns the I/O name.

Returns
String

getValue

boolean getValue ()

Gets the current value of the GPIO pin (for GPIO pins configured as input only).

Returns
boolean the state of the GPIO pin. Return value is undefined if the GPIO is configured as an output.
Throws
IOException

registerGpioCallback

void registerGpioCallback (GpioCallback callback)

Registers a callback for GPIO edge interrupts.

Equivalent to registerGpioCallback(callback, null).

Parameters
callback GpioCallback: GpioCallback to register.
Throws
IOException
IOException

registerGpioCallback

void registerGpioCallback (Handler handler, 
                GpioCallback callback)

Registers a callback for GPIO edge interrupts.

The type of edges to watch for must be first set with setEdgeTriggerType(int).

Parameters
handler Handler: Handler to run callbacks on, or null to use the current thread.
callback GpioCallback: GpioCallback to register.
Throws
IOException
IOException

setActiveType

void setActiveType (int activeType)

Sets the active level.

Parameters
activeType int: One of ACTIVE_LOW or ACTIVE_HIGH.
Throws
IOException
IllegalArgumentException
IOException

setDirection

void setDirection (int direction)

Sets the direction of the GPIO pin.

Parameters
direction int: Direction to set. One of DIRECTION_IN, DIRECTION_OUT_INITIALLY_HIGH, DIRECTION_OUT_INITIALLY_LOW.
Throws
IOException
IllegalArgumentException
IOException

setEdgeTriggerType

void setEdgeTriggerType (int edgeTriggerType)

Sets the interrupt trigger type.

The trigger type is based on the logical pin value, not the physical voltage. For example, EDGE_RISING will always trigger on a false-to-true transition, but if the GPIO is configured as ACTIVE_LOW this will actually be caused by a drop from high to low voltage.

Parameters
edgeTriggerType int: Type of trigger to use for interrupt. One of EDGE_NONE, EDGE_RISING, EDGE_FALLING, EDGE_BOTH.
Throws
IOException
IllegalArgumentException
IOException

setValue

void setValue (boolean value)

Sets the value of the GPIO pin (for GPIO pins configured as output only).

Parameters
value boolean: Value to set.
Throws
IOException

unregisterGpioCallback

void unregisterGpioCallback (GpioCallback callback)

Unregisters an interrupt callback.

Parameters
callback GpioCallback: GpioCallback to unregister.