How to make GATT client aware of changes to a characteristic?

RE: How to make GATT client aware of changes to a characteristic?

Victor Nascimento — Sun, 21 Jun 2015 13:20:38 GMT

To send data with notification, you have to do: memset(&hvx_params, 0, sizeof(hvx_params)); hvx_params.handle = p_nus->rx_handles.value_handle; hvx_params.p_data = p_string; hvx_params.p_len = &length; hvx_params.type = BLE_GATT_HVX_NOTIFICATION; sd_ble_gatts_hvx(p_nus->conn_handle, &hvx_params);

Take a look at the service file on the UART example. The file is ble_nus.c. There you can find this function to send a string.

RE: How to make GATT client aware of changes to a characteristic?

john kotkin — Sun, 21 Jun 2015 13:16:26 GMT

As i said my problem is in nRF51822 not in android because i can get answer from my android application when i use mbed.org library battery example but with battery example from nordicsemi there is no update on characteristic and i can get updated value just by requesting from android program

RE: How to make GATT client aware of changes to a characteristic?

Victor Nascimento — Sun, 21 Jun 2015 13:08:50 GMT

In my application, I follow the life-cycle:

Scan -> Connect -> Discover Services -> Subscribe to characteristic -> Idle

Then, the event comes on android as a subscription callback.

RE: How to make GATT client aware of changes to a characteristic?

john kotkin — Sun, 21 Jun 2015 13:02:30 GMT

If you mean this part hvx_params.type = BLE_GATT_HVX_NOTIFICATION; i can see it's notification on ble_bas.c service file but still i can get notification on change

RE: How to make GATT client aware of changes to a characteristic?

john kotkin — Sun, 21 Jun 2015 12:29:24 GMT

Thank you for your answer, I don't have any problem in android side my android program work okay if nrf51822 send notification for updated value but i don't get it exactly i need to look for what? these notification and indication are where in my application?

RE: How to make GATT client aware of changes to a characteristic?

Victor Nascimento — Sun, 21 Jun 2015 12:16:30 GMT

For this you have to use a Notification / Indication. Please have a look on the UART example. The TX characteristic has notification properties. On the App side, you have to subscribe to a particular characteristic and you will get an event callback whenever the BLE module writes to that characteristic.