Bluetooth LE advertising module¶

Module events
Configuration
Implementation details
- Reaction on Bluetooth peer operation
- Avoiding connection requests from unbonded centrals when bonded

Use the Bluetooth LE advertising module to control the Bluetooth LE advertising for the nRF Desktop peripheral device.

Module events ¶

Source Module	Input Event	This Module	Output Event	Sink Module
Bluetooth LE advertising module	`ble_peer_event`	`ble_adv`
Bluetooth LE state module	`ble_peer_event`
Bluetooth LE bond module	`ble_peer_operation_event`
Source modules for module_state_event	`module_state_event`
Power manager module	`power_down_event`
Buttons module	`wake_up_event`
HID forward module
Motion module
Power manager module
Wheel module
			`ble_peer_event`	Sink modules for ble_peer_event
			`ble_peer_search_event`	LED state module
			`module_state_event`	Sink modules for module_state_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 ¶

Complete the following steps to enable the Bluetooth LE advertising module:

Configure Bluetooth, as described in Bluetooth in nRF Desktop.
Define the Bluetooth device name (CONFIG_BT_DEVICE_NAME).
Define the Bluetooth device appearance (CONFIG_BT_DEVICE_APPEARANCE).
Set the CONFIG_DESKTOP_BLE_ADVERTISING_ENABLE Kconfig option.

By default, the module uses indirect advertising. Set the CONFIG_DESKTOP_BLE_DIRECT_ADV option to use directed advertising. The directed advertising can be used to call the selected peer device to connect as quickly as possible.

Note

The nRF Desktop peripheral will not advertise directly towards a central that uses Resolvable Private Address (RPA). The peripheral does not read the Central Address Resolution GATT characteristic of the central, so the peripheral does not know if the remote device supports the address resolution of directed advertisements.

Changing advertising interval ¶

Set the CONFIG_DESKTOP_BLE_FAST_ADV Kconfig option to make the peripheral initially advertise with shorter interval in order to speed up finding the peripheral by Bluetooth Centrals.

If the device uses indirect advertising, it will switch to slower advertising after the period of time defined in CONFIG_DESKTOP_BLE_FAST_ADV_TIMEOUT (in seconds).
If the device uses directed advertising, the ble_adv module will receive ble_peer_event with ble_peer_event.state set to PEER_STATE_CONN_FAILED if the central does not connect during the predefined period of fast directed advertising. After the event is received, the device will switch to the low duty cycle directed avertising.

Switching to slower advertising is done to reduce the energy consumption.

Using Swift Pair ¶

You can use the CONFIG_DESKTOP_BLE_SWIFT_PAIR option to enable the Swift Pair feature. The feature simplifies pairing the Bluetooth Peripheral with Windows 10 hosts.

Power down ¶

When the system goes to the Power Down state, the advertising stops.

If the Swift Pair feature is enabled, the device advertises without the Swift Pair data for additional CONFIG_DESKTOP_BLE_SWIFT_PAIR_GRACE_PERIOD seconds to ensure that the user does not try to connect to the device that is no longer available.

Implementation details ¶

The Bluetooth LE advertising module uses Zephyr’s Settings to store the information if the peer for the given local identity uses the Resolvable Private Address (RPA).

Reaction on Bluetooth peer operation ¶

When the Bluetooth LE bond module triggers erase advertising or Bluetooth peer change, the Bluetooth LE advertising module reacts on the received ble_peer_operation_event.

If there is a peer connected over Bluetooth, the Bluetooth LE advertising module triggers disconnection and submits a ble_peer_event with ble_peer_event.state set to PEER_STATE_DISCONNECTING to let other application modules prepare for the planned disconnection.
Otherwise the Bluetooth advertising with the newly selected Bluetooth local identity is started.

Avoiding connection requests from unbonded centrals when bonded ¶

If the Bluetooth local identity currently in use already has a bond and the device uses indirect advertising, the advertising device will not set the General Discoverable flag. If CONFIG_BT_WHITELIST is enabled, the device will also whitelist incoming scan response data requests and connection requests. This is done to prevent Bluetooth Centrals other than the bonded one from connecting with the device. The nRF Desktop dongle scans for peripheral devices using the Bluetooth device name, which is provided in the scan response data.