When to call sd_ble_gatts_hvx

Question

Hello 
 
 I am using Android and BLE communication with nRF52832 (BLENano2) now. 
 I am using SDK 15.0.0 with keil uversion. 
 Central is Android and peripheral is nRF52832. 
 Use the SDK "ble_app_blinky". 
 I now want to send arbitrary data from peripheral to central. 
 
 So I added a characteristic based on "ble_app_blinky". The following program was created for that characteristic. 
 
 uint32_t send_value(uint16_t conn_handle, ble_lbs_t * p_lbs, uint8_t sensor_value)
{
	
	if (p_lbs == NULL)
 {
 return NRF_ERROR_NULL;
 }
 
	
	uint32_t err_code = NRF_SUCCESS;
	ble_gatts_value_t gatts_value;
	
	// Initialize value struct.
 memset(&gatts_value, 0, sizeof(gatts_value));

	gatts_value.len = sizeof(uint8_t);
 gatts_value.offset = 0;
 gatts_value.p_value = &sensor_value;

	// Update database.
 err_code = sd_ble_gatts_value_set(BLE_CONN_HANDLE_ALL,////////////
 p_lbs->sensor_char_handles.value_handle,
 &gatts_value);

	
 
 if (err_code != NRF_SUCCESS)
 {
 return err_code;
 }


	
	// Send value if connected and notifying.
 if ((conn_handle != BLE_CONN_HANDLE_INVALID)) 
 {
 ble_gatts_hvx_params_t hvx_params;

 memset(&hvx_params, 0, sizeof(hvx_params));

 hvx_params.handle = p_lbs->sensor_char_handles.value_handle;
 hvx_params.type = BLE_GATT_HVX_NOTIFICATION;
 hvx_params.offset = gatts_value.offset;
 hvx_params.p_len = &gatts_value.len;
 hvx_params.p_data = gatts_value.p_value;

 err_code = sd_ble_gatts_hvx(conn_handle, &hvx_params);
 }
 else
 {
 err_code = NRF_ERROR_INVALID_STATE;
 }
 return err_code;
}

By calling this "send_value" function It turned out that a value is set by "sd_ble_gatts_value_set" and a value is notified by "sd_ble_gatts_hvx". 
 There is something I do not understand here, but I want to know when to call this function. 
 I found out that I have to be called when notification is enabled. 
 How should I program when notification is valid? 
 
 Please give me an answer

y001 · Accepted Answer

Thanks a lot for your help It solved by calling send_value in the for loop in main. I do not know if the connection will be broken with a quiet timer. It would be appreciated if you commented if there were anyone you understood.

Andy · Answer

You can call it whenever you want to update the value of a characteristic and send it to the client. 
 There are no preconditions to be able to call the function. Whether it actually sends the notification and returns success that's another question. 
 y001 said: How should I program when notification is valid? 
 I don't understand that question. 
 You should read the documentation for sd_ble_gatts_hvx() . It explains what it does very clearly. In a nutshell, it will send a notification as long as all the parameters have been setup correctly and there's space in the notification buffer (and there's a connection with notifications enabled) or otherwise it will update the attribute table (what sd_ble_gatts_value_set() does) when there's no connection or the notifications are not enabled. 
 You don't need to call sd_ble_gatts_value_set() beforehand.

Andy · Answer

y001 said: Should I put the output value from the sensor in the data_array variable of ble_nus_data_send of APP_UART_DATA_READY of uart_event_handle of main? 
 No, that example literally transforms whatever you get over UART into notifications. You need to do that somewhere else. You just need to call ble_nus_data_send on your timer timeout handler. Forget about the app uart stuff. 
 Also make sure to properly set up the data buffer before calling ble_nus_data_send().

When to call sd_ble_gatts_hvx

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