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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.

Parents
  • 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.)

Reply
  • 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.)

Children
  • 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 ?

  • Btw. any reason why using so old stack? It looks like first 6 PDU/GATT packets are going inside first connection interval while remaining 2 in next. I would expect getting TX_COMPLETE right after first 6 packets but maybe S110 waits further (e.g. because it thinks there is no time for reasonable APP processing or simply bug/limitation of the old stack). Maybe someone can test this and then compare with S130 V2? Anyway it's kind of evident that in this case you cannot expect TX_COMPLETE after each packet but only after first connection interval...

  • @run_ar Thank you for helping me out. yes, I thought of this. But the thing is that later on I am planning to send comands from master device. This way peer must receive and decode them.

    @endnode thank you for your contribution and explaining this in detail. No, I do not have any reason for using old stack. I will try s130 on my spare and compare. Right now I understand that I can not receive TX_complete event. I used this because I was not aware of other ways to notify cpu when a data packet was received.

    Could you, guys, explain me how to use sd_ble_gatts_hvx to notify cpu that a packet was received, so it proceed further?

  • No, I haven't said and I don't think you will never get TX_COMPLETE event. There is actually no other way to know that something happened on GATT layer in outbound direction so you should keep using it (the only other way would be to "shoot into the dark" by simply trying to put more outgoing notifications any time your BLE event handler is triggered by any event or based on some timer). The only thing I said is that you shouldn't expect as many TX_COMPLETE events as many packets you pushed because some of them may go through within one connection interval where there is no time for application processing between PDUs processed by Soft Device. I would simply expect that stack will trigger you as soon as at least one TX slot emptied and there is any time for APP layer processing.

    (1/2)

  • (2/2)

    Indeed I don't have time to gather any evidence that this is exactly what happens in your special case with S110 V7 or S130 V1/2 but I judge that based on my experience. You have simple options:

    1. Debug the thing on finer time scale to see exactly TX PDUs inside the connection interval and TX_COMPLETE events.
    2. Wait if someone else (e.g. Nordic support team) will invest their time into doing this for you.
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