Heart Rate collector example - how is it suppose to work?

[dragilla]

Hi, 

i'm running the Heart Rate collector example and have a question. What is the expected behaviour? From the description on the infocenter I read that it should print out the HR reading from the connected HRM. And while it does so the first time I run it on a fresh dongle, it doesn't do it the next time or any other time for that matter. I cannot figure out the difference and don't know what is going on. The following runs only print out the following info on the log:

00> <info> app_timer: RTC: initialized.
00> 
00> <info> app: Heart Rate collector example started.
00> 
00> <info> app: Starting scan.
00> 
00> <info> peer_manager_handler: Peer data updated in flash: peer_id: 0, data_id: Peer rank, action: Update, no change
00> 
00> <info> app: Connected.
00> 
00> <info> app: GATT ATT MTU on connection 0x0 changed to 23.
00> 
00> <info> peer_manager_handler: Connection secured: role: Central, conn_handle: 0, procedure: Encryption
00> 
00> <info> peer_manager_handler: Peer data updated in flash: peer_id: 0, data_id: Peer rank, action: Update, no change
00> 
00> <info> app: Data length for connection 0x0 updated to 27.
00> 
00> <info> peer_manager_handler: Connection secured: role: Central, conn_handle: 0, procedure: Encryption
00> 
00> <info> peer_manager_handler: Peer data updated in flash: peer_id: 0, data_id: Peer rank, action: Update, no change
00> 
00> <info> app: Battery Level Read as 85 %.

PS: I use the NRF52 dongle together with a j-link debugger and I'm displyaing the logs via RTT. I use the example from the SDK 17.0.2, with SD 340.

[Hung Bui]

Hi Lukasz, 

The HRS_C was made to test with the HRM example. It was not made to work with all the HRM on the market as there could be incompatibility issue. (even thought BLE standard was created to avoid such incompatibility)

Please confirm that you can use the HRM_C with the HRM example in the SDK . 

Regarding your concern about " BLE_HRS_C uses Generic Attribute Profile (0x1801):" it was just the interpretation of wireshark of the handle 0x0028 based on the service discovery process. I'm not sure why it confused and say it's Generic Attribute Profile when it's obviously not. 
From what I can see the command to enable notification are the same between the two traces:

Same with the response. 

So I'm not so sure why the Garmin didn't send the notification. 
You may need to modify the HRM so that it would behave as similar as nRF Connect to make the Garmin HRM works. 

I can see that in the hrs_c there was MTU request and LL_LENGTH_REQ, you can try to turn that off in the HRS_C firmware. Turn off pairing as well. 

Try to match as much as possible to the nRF Connect trace. 

The service discovery I don't think would cause any difference here. 

[dragilla]

Hung Bui said:

I can see that in the hrs_c there was MTU request and LL_LENGTH_REQ, you can try to turn that off in the HRS_C firmware. Turn off pairing as well. 

Can you please give me a hint where I shoul look for it? How to turn it off?

In the mean time I will try to make the HRS app work.

edit: I think I found it. In function nrf_ble_gatt_on_ble_evt:

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

    if (conn_handle >= NRF_BLE_GATT_LINK_COUNT)
    {
        return;
    }

    switch (p_ble_evt->header.evt_id)
    {
        case BLE_GAP_EVT_CONNECTED:
            on_connected_evt(p_gatt, p_ble_evt);
            break;

        case BLE_GAP_EVT_DISCONNECTED:
            on_disconnected_evt(p_gatt, p_ble_evt);
            break;

        case BLE_GATTC_EVT_EXCHANGE_MTU_RSP:
            on_exchange_mtu_rsp_evt(p_gatt, p_ble_evt);
            break;

        case BLE_GATTS_EVT_EXCHANGE_MTU_REQUEST:
            on_exchange_mtu_request_evt(p_gatt, p_ble_evt);
            break;

/*#if !defined (S112) && !defined(S312) && !defined (S122)
        case BLE_GAP_EVT_DATA_LENGTH_UPDATE:
            on_data_length_update_evt(p_gatt, p_ble_evt);
            break;

        case BLE_GAP_EVT_DATA_LENGTH_UPDATE_REQUEST:
            on_data_length_update_request_evt(p_gatt, p_ble_evt);
            break;
#endif // !defined (S112) && !defined(S312) && !defined (S122)
*/
        default:
            break;
    }
/*
    if (p_gatt->links[conn_handle].att_mtu_exchange_pending)
    {
        ret_code_t err_code;

        err_code = sd_ble_gattc_exchange_mtu_request(conn_handle,
                                                     p_gatt->links[conn_handle].att_mtu_desired);

        if (err_code == NRF_SUCCESS)
        {
            p_gatt->links[conn_handle].att_mtu_exchange_pending   = false;
            p_gatt->links[conn_handle].att_mtu_exchange_requested = true;

            NRF_LOG_DEBUG("Requesting to update ATT MTU to %u bytes on connection 0x%x (retry).",
                          p_gatt->links[conn_handle].att_mtu_desired, conn_handle);
        }
        else if (err_code != NRF_ERROR_BUSY)
        {
            NRF_LOG_ERROR("sd_ble_gattc_exchange_mtu_request() returned %s.",
                          nrf_strerror_get(err_code));
        }
    }
*/
}

Same result :(

edit2: Also, I think it's worth to note, that the Garmin has HAS the Body Sensor Location characteristic, just next to Hear Rate and the sniffer trace clearly shows an error (rcvd error response). So I think, that maybe this is the problem after all - the HRS_C is looking for both chars inside the "Gemeric Attribute Profile". I know they look the same as the Heart Rate char used by NRF Connect BLE, but there must be some difference that causes the problem. 

edit3: I can confirm it works with the BLE_APP_HRS example. But It doesn't solve my problem.

[Hung Bui]

Hi Lukasz, 

You can remove the nrf_ble_gatt.h and .c module to avoid MTU request and data length exchange. 

After you have done that, please try to compare the sniffer trace again. 

Except for the service discovery process I don't see any difference. 

If you can find away to not do service discovery from the phone (if devices are paired they wont do service discovery when reconnect) it would be even easier to match the activity from the hrs_c and the phone/PC. 

[dragilla]

I removed the gatt files but it is still the same. Also I need to discovery process in my app.

Anyway, can you try to explain why the services are recognized as insie the "Generic Attribute Profile"? They both are (body sensor location an heart rate). Looks like the dscovery process is wrong? When you view the HRM DUAL in nRF Connect BLE you can clearly see the structure of Services and I think it is in accordance to all standards.  

[Hung Bui]

My suspicion is that Wireshark recognized the service wrongly. Note that what you see there is just the interpreting of wireshark. 
That's why I suggest to find away to not doing service discovery. 

[dragilla]

Hung Bui said:

f you can find away to not do service discovery from the phone

I'm not doing a service discovery from the phone. My setup is the following:

1. NRF52840 dongle with the HRS_C demo (with modifications like removed gatt files, turned of paring and bonding, etc)

2. NRF52840 dongle with sniffer app

3. HRM Dual from Garmin

4. PC with Wireshark to sniff the traffic

The other setup, which works, is:

1. PC with NRF Connect BLE application (and correspongin NRF52840 dongle)

2,3,4 as above

So, the discovery process is done by the HRS_C app. 

Is there a way to modify it, so that it doesn't have to do service discovery and still connect to my HRM and enable notifications on it?

[Hung Bui]

You can modify the HRS_C app to not doing service discovery (please look for the ble_db_discovery_start() function in the code) and then manually do a write request to handle 0x28 to enable CCCD notification. 

On PC with nRF Connect BLE application it will do service discovery automatically. 

Please note that the nRF52 dongle that corresponding to the NRF Connect BLE app also run the same softdevice as the hrs_c .

So you can copy the whole procedure that the nRF Connect does to the HRM dual.

[dragilla]

I can disable the ble_db_discovery_start, but I need a reference to "ble_hrs_c_t * p_hrs_c" to start ble_hrs_c_hrm_notif_enable and I only get in the hrs_c_evt_handler. How do I obtain it lets say in the ble_evt_handler function to start it after the HRM is connected?

edit: I tried

m_hrs_c.conn_handle = p_ble_evt->evt.gap_evt.conn_handle;
err_code = ble_hrs_c_hrm_notif_enable(&m_hrs_c);
APP_ERROR_CHECK(err_code);

But then I get:

00> <info> app: Connected.
00> 
00> <debug> ble_hrs_c: Configuring CCCD. CCCD Handle = 0, Connection Handle = 0
00> 
00> <debug> nrf_ble_gq: Adding item to the request queue
00> 
00> <error> app: ERROR 7 [NRF_ERROR_INVALID_PARAM] at ..\..\..\main.c:275
00> 
00> PC at: 0x00038E73
00> 
00> <error> app: End of error report

the 275th line in main is the 3rd line above(APP_ERROR_CHECK)

edit2: some more debugging later...

If I do:

m_hrs_c.conn_handle = p_ble_evt->evt.gap_evt.conn_handle;
m_hrs_c.peer_hrs_db.hrm_cccd_handle = 0x28;
m_hrs_c.peer_hrs_db.hrm_handle      = 0x27;
err_code = ble_hrs_c_hrm_notif_enable(&m_hrs_c);
APP_ERROR_CHECK(err_code);

Then in nrf_ble_gq_item_add it fails in check:

if ((p_req->type >= NRF_BLE_GQ_REQ_NUM) || (conn_id == p_gatt_queue->max_conns))

The second condition is true (conn_id is 1).

edit3: I've added 

ret_code_t err_code = nrf_ble_gq_conn_handle_register(p_ble_hrs_c->p_gatt_queue, p_ble_hrs_c->conn_handle);
VERIFY_SUCCESS(err_code);

before nrf_ble_gq_item_add, and the program runs, but I'm missing a lot of data in the request.

Can you help me fill this in?