BLE Extended Advertising: Is there a way to control the delay between adv on primary channels and the extended advertisement.

RE: BLE Extended Advertising: Is there a way to control the delay between adv on primary channels and the extended advertisement.

yuxuan.cai — Thu, 14 Nov 2024 14:22:25 GMT

I see. SoftDevice Controller is developped and supported by us at Nordic. We recommend using it as it has a rich feature set and it's qualifiable. Is there a specific reason for using the Zephyr controller instead of the SDC?

To get support for the Zephyr controller, you could raise an issue here https://github.com/zephyrproject-rtos/zephyr/issues

RE: BLE Extended Advertising: Is there a way to control the delay between adv on primary channels and the extended advertisement.

JacekS — Thu, 14 Nov 2024 13:49:41 GMT

Sorry there is only one because I disabled two Primary channels doing some tests and forgot to turn them back on, but that doesn't change anything.

What I was able to find out in the meantime is that this is a behavior of the Zephyr controller, I had it in fact turned on by: CONFIG_BT_LL_SW_SPLIT=y.
Disabling it and turning on the Softdevice from Nordic by using CONFIG_BT_LL_SOFTDEVICE=y seems to change that behavior to more what I would want, the Aux Offset is now static for all primary channels with 1110us, 810us and 510us for channels 37,38 and 39 respectively.

To reproduce that it should be enough to just setup extended advertising with the SW_SPLIT turned on.

RE: BLE Extended Advertising: Is there a way to control the delay between adv on primary channels and the extended advertisement.

yuxuan.cai — Thu, 14 Nov 2024 12:28:53 GMT

Hmm there should be three consecutive ADV_EXT_INDs before the AUX_ADV_IND in an advertising event. It seems the second and the third ADV_EXT_IND (on channel 38 and 39, respectively) are missing. Are there any other ongoing roles on the advertiser?

It'll be nice if you could show how to reproduce it

RE: BLE Extended Advertising: Is there a way to control the delay between adv on primary channels and the extended advertisement.

JacekS — Thu, 14 Nov 2024 11:58:55 GMT

Thank you yuxuan.cai for your answer, I gathered some logs with Wireshark sniffer and was able to observe exactly what I described in my original post. The AuxOffset lowest value is 6300us and is increasing with every packet until it reaches around 100ms which is my advertising interval and then starts over.
This is the exact moment of it going from max to min:

Notice the time distance between 1 and 2 packet is 107940us, and between 3 and 4 it's only 6300us.
I attach the session from Wireshark:
devzone.nordicsemi.com/.../ExtAdvInt100ms.pcapng

RE: BLE Extended Advertising: Is there a way to control the delay between adv on primary channels and the extended advertisement.

yuxuan.cai — Thu, 14 Nov 2024 11:17:23 GMT

Hi,

The AUX_Offset field in the last primary channel packet (ADV_EXT_IND) should indicate when the secondary channel packet is coming. In our implementation, the AUX_Offset is 330us. Could you share the sniffer traces with us here so that we can have a better look at it?

Cheers,

Yuxuan