* Help understanding BLE Advertising and Scan Response packets...
@ 2021-05-12 1:35 Patrick Doyle
0 siblings, 0 replies; only message in thread
From: Patrick Doyle @ 2021-05-12 1:35 UTC (permalink / raw)
To: linux-bluetooth
I'm confused by how Bluez assigns data the to BLE and Scan Response
packets. In src/advertising.c, in the refresh_legacy_adv() function,
I see the following:
adv_data = generate_adv_data(client, &flags, &adv_data_len);
..
scan_rsp = generate_scan_rsp(client, &flags, &scan_rsp_len);
Looking in generate_adv_data() and generate_scan_rsp(), I see that
they both end with:
return bt_ad_generate(client->data, len);
So, then I look at bt_ad_generate() in src/shared/ad.c and I see code
much like the following:
serialize_service_uuids(ad->service_uuids, adv_data, &pos);
serialize_solicit_uuids(ad->solicit_uuids, adv_data, &pos);
serialize_manuf_data(ad->manufacturer_data, adv_data, &pos);
serialize_service_data(ad->service_data, adv_data, &pos);
serialize_name(ad->name, adv_data, &pos);
serialize_appearance(ad->appearance, adv_data, &pos);
serialize_data(ad->data, adv_data, &pos);
return adv_data;
From inspecting the code, it seems to me that Bluez stuffs the same
data in both the advertising_data packet, and in the scan_repsonse
packet. This is especially confusing to me because, examining the
packets on the air with a BLE sniffer, that is NOT what I see... but I
can't figure why not.
On a somewhat related note, I have constructed my D-Bus object with
its org.bluez.LEAdvertisement1 interface to specify the data I want in
my BLE peripheral advertising packet, and I overflowed the size of the
advertising_data packet. I would like to figure out how to indicate
to Bluez that I would like the "service_data" portion of my
advertisement to go into the scan_response packet instead of the
advertising_data packet. Any tips on how to do that?
Thanks
--wpd
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2021-05-12 1:35 Help understanding BLE Advertising and Scan Response packets Patrick Doyle
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