Subrating Sample - packets per connection event

[bluetoothmdw]

I'm running the subrating sample (ncs\v3.1.1\nrf\samples\bluetooth\subrating) on two nRF54L15-DK boards. Using a protocol analyzer I'm seeing that when the subrate factor is 10, meaning that every 10th connection event can be actively used, only one packet is transmitted and one received. The connection interval is 10 ms and transmission generally takes about 88 us and receiving a packet, only 44 us.

I realise the Bluetooth Core Specification only stipulates that a single packet must be transmitted at least and that anything else is an implementation decision, but is there a way to "encourage" Zephyr to schedule more packets per event than just one each way?

Thanks in anticipation.

[Kenneth]

Hello,

Do the more data (MD) bit indicate more data is buffered and should be sent? Normally more data is sent if there are packets buffered.

Kenneth

[bluetoothmdw]

Aha! So obvious :-) You're correct. MD is 0 on both sides so the connection event is terminated. Is there a way in code to encourage the controller to use more of the event and set MD to 1 for a certain number of packets?

[Kenneth]

Hi,

Normally MD will be set to 1 if there are any more packets buffered on a peer, and the event will be extended to allow those to be sent during the specific event. 

There are two kconfig options you can check here:

CONFIG_BT_CTLR_SDC_MAX_CONN_EVENT_LEN_DEFAULT and 
CONFIG_BT_CTLR_SDC_CONN_EVENT_EXTEND_DEFAULT.

The first set the default allocated time in us, and the second allow the event to be extended beyond the default allocated time.

Kenneth

[bluetoothmdw]

Thank you, I'll give that a try.