RE: iPhone 7, nrf52, and BLE_GATTS_EVT_EXCHANGE_MTU_REQUEST never sent

mfdevzone — Mon, 21 May 2018 23:23:29 GMT

I will respond to and close my own question. What we were seeing is that on iPhone 7 the codepath would NOT HIT the BLE_GATTS_EVT_EXCHANGE_MTU_REQUEST. What was found to be missing was any handling (and therefore, any response) to the preceding BLE_GAP_EVT_DATA_LENGTH_UPDATE_REQUEST message. I added this snipped to my handler:

    case BLE_GAP_EVT_DATA_LENGTH_UPDATE_REQUEST:
    {
        ble_gap_data_length_params_t dl_params;
        memset(&dl_params, 0, sizeof(ble_gap_data_length_params_t));
        uint32_t err_code = sd_ble_gap_data_length_update(
            ble_evt->evt.gap_evt.conn_handle,
            &dl_params, NULL);
        APP_ERROR_CHECK(err_code);
    }
    break;

And this allows the handshake sequence to complete on iPhone 7.

NOTE: I have no idea why this works, other than the request is at least handled.

Useful additional tickets:

https://devzone.nordicsemi.com/f/nordic-q-a/32460/nrf5-sdk-14-2-0-cannot-be-connected-by-ios/126444#126444

devzone.nordicsemi.com/.../nrf_ble_gatt_max_mtu_size-23-and-backwards-compatibility