How to correctly receive a value sent by notification, on my nRF51 DK

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Wed, 04 May 2016 11:56:27 GMT

Sorry i have another question ^^' Please @Petter tell me if it's necessary to open new posts or if here it's ok! Now i am sure that i'm broadcasting the correct UUID because i made the two devices connect by finding the UUID of the beacon, on the DK; the problem is that even having the correct UUID, i can't make the db discovery module to work correctly. I subscribed to theble_db_discovery_evt_register with the correct service UUID that i have on the beacon, but still checking with the printf in different part of the code, it doesn't even enter in db_disc_handler. I updated the zip file with the project currently working with the connection, can you please tell me where is the error? Thanks really again!

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Tue, 03 May 2016 13:05:37 GMT

Yes that doubt is ok, if i have more problems i will open other dedicate questions :) Thanks mr Myhre!

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Petter Myhre — Tue, 03 May 2016 12:59:57 GMT

I guess you deleted your comment because you figured it out :) Could you accept my answer? If you have more questions feel free to post them.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Petter Myhre — Mon, 02 May 2016 08:29:43 GMT

To be able to do a write to the CCCD you need to know its attribute handle. If you want to hack it, you can get the handle from Master Control Panel and hardcode it.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Thu, 28 Apr 2016 07:47:13 GMT

Ok really thanks again; however i would like to try both the ways for a didactical matter, with or without the DB discovery module. If i wouldn't use it, shall i simply trigger the "ble_nus_c_rx_notif_enable()" without any event sent from the discovery module? I mean, if i want to do a simpler way,in which if i connect to a device (maybe not by finding the UUID but the name of the device) i don't want to check if there is the wanted service, just enable and receive the notification due only to the fact that they connected.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Petter Myhre — Thu, 28 Apr 2016 07:12:47 GMT

The Database Discovery module is something you can choose to use to discover your service, it is not mandatory to use it. If you are using the module, then I you should register, or else it doesn't really make sense using it.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Wed, 27 Apr 2016 17:27:08 GMT

Nope, i will do it tomorrow when i can get to my desk; however it is compulsory to register/subscribe to a service to receive its notification, or i can skip it? This is just for my knowledge :) Nothing else?

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Petter Myhre — Wed, 27 Apr 2016 14:53:06 GMT

Have you registered with ble_db_discovery_evt_register()?

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Wed, 27 Apr 2016 13:08:10 GMT

Fantastic! Just to be sure, in order to tell what service is to be found, always referring to ble_app_uart_c, is it enough to substitute into ble_nus_c_on_db_disc_evt():

// Check if the NUS was discovered.
    if (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE &&
        p_evt->params.discovered_db.srv_uuid.uuid == BLE_UUID_NUS_SERVICE && //substitute with BLE_UUID_OUR_SERVICE_UUID          
       p_evt->params.discovered_db.srv_uuid.type == p_ble_nus_c->uuid_type) //substitute with BLE_UUID_TYPE_VENDOR_BEGIN

Is this enough or i need some other modifications? ^^

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Petter Myhre — Wed, 27 Apr 2016 12:21:32 GMT

Np. Exactly :)

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Wed, 27 Apr 2016 12:15:35 GMT

First of all thanks really for your time. So if i am understanding correctly, i should modify the ble_app_uart_c on the DK to tell it to discover my personal service on the beacon, which is NOT the nus service, but my custom one (formerly "our service" of the tutorial)?

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Petter Myhre — Wed, 27 Apr 2016 12:03:20 GMT

There are several ways of doing this, but I will use ble_app_uart_c as a reference.

As I mentioned above you need to discover your service, you can use the Database Discovery Module to this. See the SDK documentation and my answer here may also be helpful. ble_app_uart_c discovers the UART service, you need to discover your service. You can see that ble_db_discovery_evt_register() is called inside ble_nus_c_init().

In on_ble_evt() you can see that when you get the BLE_GAP_EVT_CONNECTED event service discovery is started with ble_db_discovery_start(). When a service is discovered db_disc_handler() will be called, which calls ble_nus_c_on_db_disc_evt(). This checks if the correct service was discovered and stores the attribute handles of the characteristic values and the CCCD. It then sends the BLE_NUS_C_EVT_DISCOVERY_COMPLETE event to ble_nus_c_evt_handler() in main.c. This event triggers ble_nus_c_rx_notif_enable() which writes 0x0001 to the CCCD of the characteristic that shall send notifications. Before the CCCD is set to 0x0001 the peripheral will not be able to send notifications.

If you get a notification from the peripheral you will get the BLE_GATTC_EVT_HVX event, in this you can find your data.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Wed, 27 Apr 2016 08:41:26 GMT

Ok thanks, i uploaded the zip:

For the central project (ble_app_uart_c), which is loaded on the DK, i used SDK 11 with softdevice s130 For the peripheral project (ble_app_beacon), which is loaded on the smart beacon kit (rev 1.0), i used SDK 7.1 (the latest compatible) with softdevice s110.

Thanks in advance!

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Petter Myhre — Wed, 27 Apr 2016 08:24:01 GMT

Please do not copy paste your complete code. If you want us to test your application, zip both your peripheral and central project and let us know what SoftDevice version and SDK version you are using.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Wed, 27 Apr 2016 08:06:37 GMT

Sorry probably i can't explain well what i have done until now. As i said in the post, i have already used those example you are suggesting (ble app uart central in particular), i will load the full code that i used on the DK (as said, it's pretty much the app uart central, on the beacon i have the service of the tutorial that sends temperature data) in the post so you can watch what i implemented.

@Jorge, yes indeed, i have a similar code but not specifically for HRS since i don't use it, i just tried to adapt the procedure for my own service.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Jorge — Wed, 27 Apr 2016 08:04:52 GMT

If you are using the ble_app_hrs_c example there is this part:

/**@brief Heart Rate Collector Handler.
 */
static void hrs_c_evt_handler(ble_hrs_c_t * p_hrs_c, ble_hrs_c_evt_t * p_hrs_c_evt)
{
    uint32_t err_code;

    switch (p_hrs_c_evt->evt_type)
    {
        case BLE_HRS_C_EVT_DISCOVERY_COMPLETE:

            // Heart rate service discovered. Enable notification of Heart Rate Measurement.
            err_code = ble_hrs_c_hrm_notif_enable(p_hrs_c);
            APP_ERROR_CHECK(err_code);

            APPL_LOG_DEBUG("Heart rate service discovered \r\n");
            break;

        case BLE_HRS_C_EVT_HRM_NOTIFICATION:
        {
            APPL_LOG_DEBUG("[APPL]: HR Measurement received %d \r\n", p_hrs_c_evt->params.hrm.hr_value);

            APPL_LOG("Heart Rate = %d\r\n", p_hrs_c_evt->params.hrm.hr_value);
            break;
        }

        default:
            break;
    }
}

this enables the notification and receives the data is on p_hrs_c_evt->params.hrm.hr_value.

this example is from SDK11. To be sure you are accessing all the steps you waant you can put some printf's on your code to see if it goes where you want!

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Petter Myhre — Wed, 27 Apr 2016 08:01:20 GMT

I suspect you think this is much less complex than it is. It is not one line of code you can put in to get this to work. You need to do service discovery, you need to enable notifications on the peripheral by writing to the CCCD of the characteristic. That is why I recommended you to have a look at the BLE central tutorial. I would also recommend you to start of with a peripheral and central example that actually works, play with them, and modify them to learn how thing works. For example ble_app_uart and ble_app_uart_c. Or ble_app_hrs and ble_app_hrs_c.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Wed, 27 Apr 2016 07:41:21 GMT

Guys i think that you are not reading the main post. I got them connecting as i clearly stated (discovery on the DK and all the stuff), and this is confirmed by the setting of a LED, the notification are also enabled but i don't receive anything, this is the problem. I am just asking at level of code, what i should write to enable the receiving of the value on the DK to see if i did all correctly.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Jorge — Wed, 27 Apr 2016 07:30:56 GMT

On the DK you need to Discover the device, connect to it, allow it to send notifications and then you should receive the data from the beacon. If you can connect, I don't understand what could be the problem for not getting the data.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Wed, 27 Apr 2016 07:28:26 GMT

So can you please indicate me the correct way, maybe with an example of instruction? By the way, this is what another member said me to do in another topic, it's not an idea of mine, and that assignation is taken from another example (heart rate service).

RE: How to correctly receive a value sent by notification, on my nRF51 DK

RichieJH — Tue, 26 Apr 2016 21:51:48 GMT

I am not sure what you are trying to achieve, but what struck me is you are assigning an address to data instead of dereferencing so I am not sure what you were hoping for at that point.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Tue, 26 Apr 2016 15:39:59 GMT

As i said, the question is, on the receiving device (that is the DK in my case..) how should i get the values notified by the beacon? Because if i use the MCP on the phone, i just connect the two devices and the values are pushed in, is it the same here? i should only get the two devices connecting? And if not,what instruction should i add? I am asking this just because the DK doesn't receive any value by notification, it doesn't even receive the "BLE_GATTC_EVT_HVX" event that i should get every time i receive a value from notification :)

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Jorge — Tue, 26 Apr 2016 15:13:08 GMT

But what are you getting there then? what is your real question?

When you edit your questions or comments try to press the box "minor" edit, if not the other persons receive a lot of messages ;)

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Revo — Tue, 26 Apr 2016 15:01:38 GMT

The tutorial says that you can put the data to be sent there where you are saying (in the code loaded on the beacon is there), but on the other side (on the DK) the received data should be in the field that i posted! Also in the heart rate example the received data is stored in:

data = &p_ble_evt->evt.gattc_evt.params.hvx.data[0];

that is what i wrote in the code.

RE: How to correctly receive a value sent by notification, on my nRF51 DK

Jorge — Tue, 26 Apr 2016 13:16:48 GMT

From what I understood from the tutorial I think the data is on

p_ble_evt->evt.gattc_evt.hvx_params.p_data;

you then can print it via NUS to your a terminal on your pc.