I'm using NCS 1.4.0 and 2 boards nRF5340PDK.
I'm using central_uart and peripheral_uart samples. Both display when connection interval change.
The central_uart use BT_LE_CONN_PARAM(6, 12, 0, 400). The peripheral_uart use default value that are:
#define CONFIG_BT_PERIPHERAL_PREF_MIN_INT 24
#define CONFIG_BT_PERIPHERAL_PREF_MAX_INT 40
When I test the samples, the connection interval is first correctly set at 12 but after 5s it change to 40. Here are the logs:
[00:00:00.419,616] <inf> fs_nvs: 2 Sectors of 4096 bytes [00:00:00.419,616] <inf> fs_nvs: alloc wra: 0, fa8 [00:00:00.419,616] <inf> fs_nvs: data wra: 0, a4 [00:00:00.435,913] <wrn> bt_hci_core: ECC HCI commands not available [00:00:00.435,913] <inf> bt_hci_core: No ID address. App must call settings_load() [00:00:00.435,913] <inf> peripheral_uart: Bluetooth initialized [00:00:02.537,567] <inf> peripheral_uart: Connected ea:b6:af:d6:f9:b3 (random) [00:00:02.537,597] <inf> peripheral_uart: Connection interval: 12 [00:00:02.644,195] <inf> peripheral_uart: Security changed: ea:b6:af:d6:f9:b3 (random) level 2 [00:00:07.863,861] <inf> peripheral_uart: Connection interval: 40
[00:00:00.373,046] <inf> fs_nvs: 2 Sectors of 4096 bytes [00:00:00.373,046] <inf> fs_nvs: alloc wra: 0, fc0 [00:00:00.373,046] <inf> fs_nvs: data wra: 0, 88 [00:00:00.389,709] <wrn> bt_hci_core: ECC HCI commands not available [00:00:00.389,739] <inf> bt_hci_core: No ID address. App must call settings_load() [00:00:00.389,739] <inf> central_uart: Bluetooth initialized [00:00:00.392,120] <inf> central_uart: Scan module initialized [00:00:00.392,120] <inf> central_uart: NUS Client module initialized [00:00:00.398,925] <inf> central_uart: Scanning successfully started [00:00:00.465,423] <inf> central_uart: Filters matched. Address: e6:a7:8c:4b:48:5c (random) connectable: 0 [00:00:00.566,070] <inf> central_uart: Connected: e6:a7:8c:4b:48:5c (random) [00:00:00.566,070] <inf> central_uart: Connection interval: 12 [00:00:00.672,668] <inf> central_uart: Security changed: e6:a7:8c:4b:48:5c (random) level 2 [00:00:00.957,519] <inf> central_uart: Service discovery completed [00:00:05.892,486] <inf> central_uart: Connection interval: 40