RE: [CLOSED][nrf52832][S132 4.0.0] connection fails: exchange MTU request is not received on evt.common_evt.conn_handle=2

ffreturn — Mon, 24 Apr 2017 07:05:31 GMT

Thanks for your answer. Problem is fixed.

RE: [CLOSED][nrf52832][S132 4.0.0] connection fails: exchange MTU request is not received on evt.common_evt.conn_handle=2

FormerMember — Fri, 21 Apr 2017 13:13:58 GMT

The reason that there only will a be MTU request/exchange for the two first links (0x00 and 0x01) is because of the default values used by the nrf_ble_gatt module.

nrf_ble_gatt_on_ble_evt(..) in nrf_ble_gatt.c looks like the following:

void nrf_ble_gatt_on_ble_evt(nrf_ble_gatt_t * p_gatt, ble_evt_t const * p_ble_evt)
{
    uint16_t conn_handle = p_ble_evt->evt.common_evt.conn_handle;

    if (conn_handle >= NRF_BLE_GATT_LINK_COUNT)
    {
        return;
    }
...

The nrf_ble_gatt module will only do an action if conn_handle < NRF_BLE_GATT_LINK_COUNT. The root cause of the problem is how NRF_BLE_GATT_LINK_COUNT is set in nrf_ble_gatt.h:

#define NRF_BLE_GATT_LINK_COUNT (NRF_BLE_PERIPHERAL_LINK_COUNT + NRF_BLE_CENTRAL_LINK_COUNT)

Since both NRF_BLE_PERIPHERAL_LINK_COUNT and NRF_BLE_CENTRAL_LINK_COUNT by default only are defined in nrf_ble_gatt.h, their value is not related to the actual project settings, but instead the default value of '1'. Therefore, NRF_BLE_GATT_LINK_COUNT is by default '2', and there the module will only do MTU request/exchange for the two first links. Changing the value of NRF_BLE_PERIPHERAL_LINK_COUNT and NRF_BLE_CENTRAL_LINK_COUNT to the correct values will solve the problem.

When "re-defining" NRF_BLE_PERIPHERAL_LINK_COUNT and NRF_BLE_CENTRAL_LINK_COUNT, I would recommend to do so in sdk_config.h.