Problem queuing notifications

[Adriana]

Hi,

I am working on a project of throughput data from sensors to my central via nrf52832 through a notifying service (SDK14.0.0, S132).

As explained in several questions of this site, I use the BLE_GATTS_EVT_HVN_TX_COMPLETE event as trigger for queuing my data packets. At connection I'm sending, triggered by a timer, a 20 bytes packet just for receiving the first tx_complete_event . All right up to this point.

The problem appears when I try to send several packets per connection event. What I am doing is calling sd_ble_gatts_hvx in a loop routine for queuing 4 packets of 20 bytes. It works fine for the first transmission (the one after the timer-triggered transmission) but after that I only receive, at my sniffer, the first packet for each connection.

BLE_GATTS_HVN_TX_QUEUE_SIZE_DEFAULT is equal to 6, I have been trying several connection intervals.

Maybe I have misunderstood the way notifications work, so I will appreciate any help.

[endnode]

No, you are doing it correctly. There are at least two explanations:

• Your sniffer is missing multiple packets per connection interval.
• One of the sides don't support more then one PDU per connection interval.

Both can be debugged easily: make some dummy transfer of long queue which contains easily distinguishable packets (e.g. 0x00010203...FF cut into 20-byte blocks), perform the transfer and look into sniffer's trace. You should see what is in first packet of each interval and also you should be able to see MD (More Data) bits in each PDU header showing which side cannot receive more packets at given interval.

[Adriana]

Thank you for your help and you debug suggestion, that's actually what I am doing. But I'm not sure how to check the MD bit state.

I am using a Raspberry pi model B as sniffer and tracking packets with Wireshark (Encapsulation type: Bluetooth H4 with linux header (99)) and I can see data packets preceded by 12 bytes:

• HCI packet type (1byte)
• BC flag (2bytes)
• data total length (2bytes)
• length (2bytes)
• CID (2bytes)
• Method (1byte)
• Handle (2bytes)

but I can't relate this information with MD bit. Can you give me some advice?

Thank you