Function key module

The Function key module applies the Fn key modifier to activate special functions assigned to dual-purpose keys.

Module events

Source Module	Input Event	This Module	Output Event	Sink Module
Buttons module	button_event	fn_keys
Button simulator module
Function key module
Source modules for module_state_event	module_state_event
			button_event	Sink modules for button_event
			module_state_event	Sink modules for module_state_event

Note

See the Application overview for more information about the event-based communication in the nRF Desktop application and about how to read this table.

Configuration

The module uses button_event sent by CAF: Buttons module. Make sure mentioned CAF module is enabled.

The module is enabled with CONFIG_DESKTOP_FN_KEYS_ENABLE option.

You must configure the following options:

• CONFIG_DESKTOP_FN_KEYS_SWITCH - Fn key button.

• CONFIG_DESKTOP_FN_KEYS_LOCK - Fn lock button.

• CONFIG_DESKTOP_STORE_FN_LOCK - Option for defining if the device should store the Fn lock state after reboot (set by default to storing the state).

• CONFIG_DESKTOP_FN_KEYS_MAX_ACTIVE - Maximum number of dual-purpose keys pressed at the same time (8 by default). The module remembers the pressed keys to send proper key releases.

In the file fn_keys_def.h, define all the dual-purpose keys. The fn_keys array must be sorted by key ID (the module uses binary search).

By default, the module subscribes for button_event as the first subscriber (APP_EVENT_SUBSCRIBE_FIRST). You can disable the CONFIG_DESKTOP_FN_KEYS_BUTTON_EVENT_SUBSCRIBE_FIRST Kconfig option to use early subscription (APP_EVENT_SUBSCRIBE_EARLY).

Implementation details

The module replaces the key ID for the dual-purpose keys when the Fn modifier is active (that is, when the Fn key is pressed or the Fn lock is active, but not both). The original button_event is consumed and the new event of the same type is submitted, but with remapped button_event.key_id.