Application service UUID gone after secure OTA DFU

[SK]

Hello, 

I am using nRF52832 on SES v4.12 with SDK v15.3 and SD v6.1.1 on a custom board.

Background: 

I want to perform OTA DFU and with that i have two services enabled (secure dfu buttonless and NUS). I was facing OTA DFU issue in which i was getting CRC does not match error. This has been resolved here - https://devzone.nordicsemi.com/f/nordic-q-a/55653/dfu-crc-does-not-match-error

So, i have been able to perform OTA update. 

The package that i created includes BL+SD+APP. 

Problem: 

Once i perform the update and connect again, i only see one service, which is Secure DFU service and the other which is the main application service ID (NUS) is gone. I looked in the forum and found this -https://devzone.nordicsemi.com/f/nordic-q-a/39982/after-ota-dfu-bootloader-application-gone

But i do not quite fully understand as to what is to be done here. Could you please highlight on what is required for a proper DFU process? From what i understand from the post and infocenter that it is still a single update, so BL+SD+APP merged together should work fine internally. 

EDIT:

Zip created has only application hex in it. BL+SD+APP is programmed directly using nrfjprog. 

Please let me know if you require more information. 

Thanks a lot!

-SK

[Hung Bui]

@SK: The issue regarding the MTU request is fixed in SDK v16.0 but not on SDK v15.3 you may want to follow my suggestion in the case. 

[SK]

Okay sure, will do. In that case, you say putting in a timer to delay the MTU exchange? When should the timer expire? Could you tell me more on the details, please.  

[Hung Bui]

The main reason to delay MTU exchange was to wait for the phone to do that. (so that we have larger MTU ATT). I would say give it 1-2 second. 

Regarding the issue of having sd_ble_gatts_service_changed() and sd_ble_gattc_exchange_mtu_request() at the same time, you can check if the error is NRF_ERROR_INVALID_STATE the application can retry after a certain time (let's say 1 second) . 

[SK]

Hi Hung Bui

Sorry, i had to move to some other tasks. I tried to do as you suggested, but i am getting error on the sd_ble_gattc_exchange_mtu_request() --> unknown error code 

Would you know why would that be? I have added timer as below.

    if (p_link->att_mtu_desired > p_link->att_mtu_effective)
    {
        NRF_LOG_DEBUG("Requesting to update ATT MTU to %u bytes on connection 0x%x.",
                      p_link->att_mtu_desired, conn_handle);
        create_mtu_request_timer();
        app_timer_start(mtu_request_delay_timer, APP_TIMER_TICKS(1000), NULL);
    }

Rest of the code i have moved in the handler:

static void request_delay_handler(void *p_context)
{
  ret_code_t err_code;
  nrf_ble_gatt_t * p_gatt = (nrf_ble_gatt_t *)p_context;
  ble_evt_t const * p_ble_evt;
  uint16_t  conn_handle = p_ble_evt->evt.common_evt.conn_handle;
  nrf_ble_gatt_link_t * p_link      = &p_gatt->links[conn_handle];
    err_code = sd_ble_gattc_exchange_mtu_request(conn_handle, p_link->att_mtu_desired);

    if (err_code == NRF_SUCCESS)
    {
        p_link->att_mtu_exchange_requested = true;
    }
    else if (err_code == NRF_ERROR_BUSY)
    {
        p_link->att_mtu_exchange_pending = true;
        NRF_LOG_DEBUG("sd_ble_gattc_exchange_mtu_request()"
                      " on connection 0x%x returned busy, will retry.", conn_handle);
    }
    else
    {
        NRF_LOG_ERROR("sd_ble_gattc_exchange_mtu_request() returned %s.",
                      nrf_strerror_get(err_code));
    }  
}

Once i connect, i get this error: 

<error> nrf_ble_gatt: sd_ble_gattc_exchange_mtu_request() returned Unknown error code.

[SK]

Okay, got it what i was doing wrong there! 

will continue to check on the DFU procedure now.