Observe NRF_BLE_GATT_EVT_ATT_MTU_UPDATED event in gatt central app

[esonhon]

Hello,

I am working on a  project that modified from ble_app_uart_c, with sdk v16.0, softdevice S140

In my case, I defined an event observer by 

NRF_SDH_BLE_OBSERVER(m_ble_observer, APP_BLE_OBSERVER_PRIO, ble_evt_handler, &m_scan); in initial routine.

And

/**@brief Function for handling events from the GATT library. */
static void gatt_evt_handler(nrf_ble_gatt_t * p_gatt, nrf_ble_gatt_evt_t const * p_evt)
{
if (p_evt->evt_id == NRF_BLE_GATT_EVT_ATT_MTU_UPDATED)
{
printf("ATT MTU exchange completed.\n");

m_ble_nus_max_data_len = p_evt->params.att_mtu_effective - OPCODE_LENGTH - HANDLE_LENGTH;
printf("Ble NUS max data length set to 0x%X(%d)\n", m_ble_nus_max_data_len, m_ble_nus_max_data_len);
}
}

/**@brief Function for initializing the GATT library. */
void gatt_init(void)
{
ret_code_t err_code;

err_code = nrf_ble_gatt_init(&m_gatt, gatt_evt_handler);
APP_ERROR_CHECK(err_code);

err_code = nrf_ble_gatt_att_mtu_central_set(&m_gatt, NRF_SDH_BLE_GATT_MAX_MTU_SIZE);
APP_ERROR_CHECK(err_code);
}

Just want to observe NRF_BLE_GATT_EVT_ATT_MTU_UPDATED event, but the event handler gatt_evt_handler never triggered.

Have tried to put NRF_BLE_GATT_EVT_ATT_MTU_UPDATED event handler in ble_evt_handler defined above, not working. But other event such as BLE_GATTC_EVT_TIMEOUT can be triggered in this handler.

Thanks.

[Sigurd]

Hi,

Maybe the peripheral you are connecting to does not support long ATT MTU?

What do you get in the log if you set NRF_LOG_DEFAULT_LEVEL to 4 in sdk_config.h ?

Check what is happening on-air with a sniffer trace: https://www.nordicsemi.com/Products/Development-tools/nrf-sniffer-for-bluetooth-le

[esonhon]

Hi,

Thanks for your advice, the peripheral support long MTU, when I use the official demo, it will catch the event. I'll try to set log level 4 and see what happens.

[esonhon]

Hi, Sigurd,

I traced the connection procedure, and got a key question:

If I use NRF_SDH_BLE_OBSERVER(m_ble_observer, APP_BLE_OBSERVER_PRIO, ble_evt_handler, NULL) to register an event handler  ble_evt_handler, the GATT relevant event such as BLE_GAP_EVT_CONNECTED should be/could be passed to the default event handler nrf_ble_gatt_on_ble_evt in nrf_ble_gatt.c?

Thanks.

[Sigurd]

Hi,

esonhon said:

If I use NRF_SDH_BLE_OBSERVER(m_ble_observer, APP_BLE_OBSERVER_PRIO, ble_evt_handler, NULL) to register an event handler  ble_evt_handler, the GATT relevant event such as BLE_GAP_EVT_CONNECTED should be/could be passed to the default event handler nrf_ble_gatt_on_ble_evt in nrf_ble_gatt.c?

Yes, all observers should get the BLE event.