Buttons module

The buttons module is responsible for generating events related to key presses. The source of events are changes to GPIO pins.

Module events

Source Module	Input Event	This Module	Output Event	Sink Module
Power manager module	power_down_event	buttons
Source modules for module_state_event	module_state_event
Buttons module	wake_up_event
HID forward module
Motion module
Power manager module
Wheel module
			button_event	Function key module
				Motion module
				Button simulator module
				Click detector module
				Passkey module
				HID state module
			module_state_event	Sink modules for module_state_event
			wake_up_event	Sink modules for wake_up_event

Note

See the Overview: Firmware architecture for more information about the event-based communication in the nRF Desktop application and about how to read this table.

Configuration

The module is enabled with the CONFIG_DESKTOP_BUTTONS_ENABLE define.

The module can handle both matrix keyboard and buttons connected directly to GPIO pins.

When defining how buttons are connected, two arrays are used, both defined in the buttons_def.h file that is located in the board-specific directory in the application configuration directory:

• The first array contains pins associated with matrix rows.

• The second array contains pins associated with columns, and it can be left empty (buttons will be assumed to be directly connected to row pins, one button per pin).

By default, a button press is indicated by the pin switch from the low to the high state. You can change this with CONFIG_DESKTOP_BUTTONS_POLARITY_INVERSED, which will cause the application to react to an opposite pin change (from the high to the low state).

Implementation details

The module can be in the following states:

• STATE_IDLE

• STATE_ACTIVE

• STATE_SCANNING

• STATE_SUSPENDING

After initialization, the module starts in STATE_ACTIVE. In this state, the module enables the GPIO interrupts and waits for the pin state to change. When a button is pressed, the module switches to STATE_SCANNING.

When the switch occurs, the module submits a work with a delay set to CONFIG_DESKTOP_BUTTONS_DEBOUNCE_INTERVAL. The work scans the keyboard matrix for changes to button states and sends the related events. If the button is kept pressed while the scanning is performed, the work will be re-submitted with a delay set to CONFIG_DESKTOP_BUTTONS_SCAN_INTERVAL. If no button is pressed, the module switches back to STATE_ACTIVE.

When the system enters the low-power state, the buttons module goes to STATE_IDLE, in which it waits for GPIO interrupts that indicate a change to button states. When an interrupt is triggered, the module will issue a system wake-up event.

If a request for power off comes while the button is pressed, the module switches to STATE_SUSPENDING and remains in this state until no button is pressed. Then, it will switch to STATE_IDLE.