Check if a certain packet has been transmitted

Question

Hello Nordic! In my FW, I need to know when a specific packet has been actually sent (because of SD packet buffering). I am able to receive the BLE_EVT_TX_COMPLETE event, but that provides no information regarding the contents of the packet that was sent. The packet are being sent using notifications. 
 To achieve this, I was
I'm using an thinking about checking the SD buffer status just before requesting the transmission of the packet of interest (say there were x packet on the buffer). Then, I would count down how many TX_COMPLETE were received since the transmission was requested ( x-- ), and when x==0 the packet had been sent. My question is how do I access the status of the SD TX buffer. 
 Is there a better method to know when a packet has been sent? Indications could be a possibility, but I would like to avoid them if possible. 
 I'm using a nRF51822 along with SDK6.1 and s110 v7.3.0.

RK · Accepted Answer

All you need to do is keep track of the TX_COMPLETE messages coming in, each one of those represents the completion of the send, in order, of the packets you sent out. So if you have 4 packets in-flight, the first TX_COMPLETE represents the first of those having been sent. So just keep whatever information you want about your packets in an array or ring buffer or something, as you send a new one add it to the list, as a TX_COMPLETE comes in, remove the first one and process it. 
 Or if the use case is as simple as you state above, and you just want to know for a certain packet occasionally when it's been transmitted, just keep a tally of packets in-flight incrementing each time you send one and decrementing each time you get TX_COMPLETE, that number is the current status of packets in-flight, no need to query the softdevice (and you can't anyway).

Check if a certain packet has been transmitted

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