How to force the notification to turn on from the server not the client?

[June6]

uint16_t buffer[4];
	
buffer[0] = p_nus->handles1.cccd_handle;                  // cccd handle
buffer[1] = 2;                                            // cccd attribute size = 2
buffer[2] = 1;                                            // 1 = enable notifications
buffer[3] = crc16_compute((uint8_t *)buffer, 6, NULL);     // CRC-CCITT (0xFFFF)
err_code = sd_ble_gatts_sys_attr_set(p_ble_evt->evt.gap_evt.conn_handle, (uint8_t*)(buffer), 8, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS); 

if(err_code == NRF_SUCCESS)
{
    p_client->is_notification_enabled1 = true;  // Enable notification
}

I add this code in 'static void on_connect(ble_nus_t * p_nus, ble_evt_t const * p_ble_evt) '  on the sever. But I still got an err_code NRF_ERROR_INVALID_DATA. Softdevice is s132nrf52611. Any suggestions to force the notification? I use the SDK version 15.3.0.

[June6]

There is an error in the above description, softdevice is S140 nRF52840.

[Karl Ylvisaker]

Hello,

Any suggestions to force the notification?

I am not sure I understand exactly what you mean here.

A server / peripheral may not force the client / central to accept notifications. The notification has to be enabled by the central / client itself, before the peripheral / server can start sending notifications.
The only time that the peripheral may send notifications "unprompted" to the central, is if the two devices are bonded, and the central has enabled the notification in a previous connection.
Perhaps if you could detail your problem or use-case some more, I would be able to advise you better.

If this is not what you were asking about, please elaborate on what you would like to achieve.

Best regards,
Karl 

[June6]

Hi Karl

I want to achieve the effect of using NRF connect to automatically enable notification as soon as Bluetooth is connected, without needing to click the button on the app. I have successfully implemented this effect in the sample program(uart).  But in my project, I changed the characteristic UUID and added notify write and write_no_resp to both of them.

[June6]

My customer has a product that uses ti's Bluetooth chip, which can automatically enable notification and send data once Bluetooth is connected, without clicking the enable notification button on the app. The customer wants to achieve the same effect.

[Karl Ylvisaker]

Thank you for elaborating, now I understand what you meant originally!

If you would like nRF Connect ( for desktop? ) to automatically reconnect and receive notifications, you need to use the autoConnect feature, and bonding. Bonding will ensure that the notification-enabled information is kept between connections, and autoConnect will automatically connect to your peripheral.
You should then configure your GATT client ( in the nRF Connect application ) to enable notifications for the custom service you have created.

June6 said:

My customer has a product that uses ti's Bluetooth chip, which can automatically enable notification and send data once Bluetooth is connected,

This does not have anything to do with the particular manufacturer, since it is a feature of the BLE specification.
You can see an example of how this is implemented in an example in the unmodified ble_app_uart_c example from the SDK.

Best regards,
Karl