Advertising via coded PHY

[gab987]

Hi, i want to use the coded PHY for advertising but cannot get it working. I configure the advertising source with these params:

const struct bt_le_adv_param* ext_adv_param = BT_LE_ADV_PARAM(BT_LE_ADV_OPT_EXT_ADV | BT_LE_ADV_OPT_CODED, ext_adv_interval, ext_adv_interval, NULL);

and start the scanning of the sink like this:

err = bt_le_scan_start(BT_LE_SCAN_CODED_ACTIVE, NULL);

The advertising starts without any errors but the sink does not find the advertising. When I confiure the bt_le_adv_params without BT_LE_ADV_OPT_CODED or with BT_LE_ADV_OPT_NO_2M
it works as expected. I am using the nordic softdevice controller.

Am I missing something?

[Vidar Berg]

Hi,

Do you have logging enabled to see if bt_le_scan_start() returning an error code or not? I would also recommend you have a look at the central_hr_coded sample in the SDK to compare the configurations.

Best regards,

Vidar 

[gab987]

I think I found the combination of issues. For context I am trying to send/receive Broadcast isochronous streams.

1. I added the `CONFIG_BT_CTLR_PHY_CODED` and `CONFIG_BT_EXT_ADV_CODING_SELECTION` to the `prj.conf` of both controller, which is weird, since i was able to create/connect to BIS on the coded PHY without those options
2. I introduced a delay on the broadcast source source between the start of the periodic + extended advertising and the creation of the BIG. I think the receiver cannot find the advertisement when the source is streaming. When the stream is started immediately after the advertisement is started the receiver cannot find the advertisement.

[gab987]

I just checked on the logs for the bis source app + controller and the bis sink app + controller and there are no error messages. The controller just spits out the `hci_ipc: Sent/Received messages of x bytes.` and the app does not print any error/warnings and does not return any error values.

[Vidar Berg]

Sorry for the delay. Have you made any progress on this in the meantime? If not, could you point me to the exact SDK samples you used as a starting point? 

gab987 said:

When the stream is started immediately after the advertisement is started the receiver cannot find the advertisement.

Does this mean that it works with coded PHY when the stream is not started?

[gab987]

No, i did not make any progress.

I started out using the zephyr/bap_broadcast_(source/sink) samples and modified them.

[gab987]

And yes, i was able to find the advertisement when no stream was running.

[Vidar Berg]

I checked with the developers, it turns out you can have a valid BIG that uses all the airtime from the advertiser without HCI error. Could you please provide us with the parameters you are using for the broadcast source?

[gab987]

Hey, sorry for the late response.

I used different values for the broadcast parameters where i changed values like .num_subevents, .irc and .pto in the bt_iso_big_create_param and bt_iso_chan_qos structures. 
On coded phy i only tested values where .irc = .pto = .nse = 1 and .pdu = .pdu is on of 30/40/80.

[Vidar Berg]

Thanks. I got this feedback from one of the developers in response the parameters you used:

• Change parameters to BN=2, NSE=2, double their current iso interval (keep SDU interval the same). Note, this will increase the latency but improve amount of air time available. This could be increased further if latency is not an issue e.g. BN=3. NSE=3. triple the current iso_interval, BN=4, NSE=4, four times the iso_interval...
• Change the advertiser to use coding=s2 if this is acceptable to the customer. Unfortunately, we do not currently support s2 on BIG