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How to receive BLE_EVT_TX_COMPLETE faster?

Greatings!

I am sending a packet with data in it from my custom board with nrf51822 to my android phone using cahnged ble_app_uart. The packet is being sent 8 times before I receive event BLE_EVT_TX_COMPLETE. Is it possibile to reduce time for receiving BLE_EVT_TX_COMPLETE or could you suggest how to wait for this event so I would not be sending 8 packets? This is where I set event flag:

case BLE_EVT_TX_COMPLETE:
        ble_tx_complete = 1;					
	    break;

Is device is connected I am sending a string while I will get an event flag:

if( m_conn_handle != BLE_CONN_HANDLE_INVALID ) // BLE is connected. Do service routine.
	 {					
	  if(ble_tx_complete == 0) 
	    {
	      sprintf((char*)siusti_plnasete0,"H:%.2f T:%.2f",BME280_humidity,BME280_temperature);
	      ble_nus_send_string(&m_nus,siusti_plnasete0,20);
            }
	 }

This is how it looks in nrf_uart app:

image description

I have tried this way but then phone do not receive that packet at all:

 if( m_conn_handle != BLE_CONN_HANDLE_INVALID ) // BLE is connected. Do service routine.
    	 {					
    	
    	      sprintf((char*)siusti_plnasete0,"H:%.2f T:%.2f",BME280_humidity,BME280_temperature);
    	      ble_nus_send_string(&m_nus,siusti_plnasete0,20);
                 while(ble_tx_complete == 0) 
    	       {
                   }
    	 }

Any suggestions?

-----------------------EDIT----------------------------------------------- This is real time trace from wireshark:

image description

I use s110 (7.0.0), I can not find which SDK example I took. Is there a way to find from which sdk it was taken somewhere in a project? But I believe its one of 5,6 or 7.

  • Do you have any real-time trace where you would correlate on-air packets and SoftDevice BLE events? Because you will typically get the event after connection interval is over and if your stack transports more then on PDU in the interval there is now way to have this event in between (but also that's not an issue for you because there is no time to do anything with it anyway, timing during the ongoing connection event is too strict and fast for application processing between packets). But 8 PDUs look suspicious because that should need more then one connection interval even if your stack sends multiple packets (because typical limit is 6 not 8).

  • Not sure I understand the problem here. But why would you use the tx_complete event to determine when to send another packet? I.e. If you only want to send the packet once, you should only call the sd_ble_gatts_hvx one time. The packet is buffered in the SD until it's received by the peer or the connection is disconnected.

    If you want to send one packet per connection event you could use radio notifications to let your application know when to prepare the next packet.

    If you want to send data as fast as possible, just loop through your date until the Softdevice buffers are full (7 or 6 if you sent packets in the previous connection event.)

  • It is my bad to not making it clear that I want it to send one time and then wait till I know that master have received it. After that while being in the same connection I would like to send more data. Would it be possibile using sd_ble_gatts_hvx? Should I use it as in [this example] ? (devzone.nordicsemi.com/.../) or I should send it using ble_nus_send_string and wait for indication in sd_ble_gatts_hvx? Could make explain more details how should I use sd_ble_gatts_hvx ?

  • Have you considered using indications for this instead? I.e. application layer acknowledgement. The drawback is that it is slower than notification.

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