Multiple service UUIDs in advertising packet array (NCS)

[zciwor]

I'm developing a BLE project using Zephyr NCS and I am having trouble advertising multiple custom services. The sample applications are configuring advertising data using the following arrays:

static const struct bt_data ad[] = {}

and 

static const struct bt_data sd[] = {}

There's a number of different elements in the array depending on the example application. I can't seem to find any clear documentation on how to properly define these arrays for my advertising information. I have a mix of 16bit and 128bit UUIDs that I would like to advertise. The HID keyboard example has the following code in the bt_data ad[] array:

BT_DATA_BYTES(BT_DATA_UUID16_ALL,
		      0x12, 0x18,       /* HID Service */
		      0x0f, 0x18),

But, when I replicate this structure like so: 

#define MY_SERVICE_UUID 0xd4, 0x86, 0x48, 0x24, 0x54, 0xB3, 0x43, 0xA1, \
			            0xBC, 0x20, 0x97, 0x8F, 0xC3, 0x76, 0xC2, 0x75
			            
#define MY_OTHER_SERVICE_UUID 0xd4, 0x86, 0x48, 0x24, 0x54, 0xB3, 0x43, 0xA1, \
			            0xBC, 0x20, 0x97, 0x8F, 0xC3, 0x76, 0xC2, 0x73

BT_DATA_BYTES(BT_DATA_UUID128_ALL, MY_SERVICE_UUID, MY_OTHER_SERVICE_UUID),

My device fails with the following error: Advertising failed to start (err -22)

What am I missing here? Are there any good resources explaining how to configure my advertising data? 

[Simon]

Hello,

I'll take a look at this tomorrow

Best regards,

Simon

[Simon]

Be aware that the maximum amount of bytes the advertising data can contain is 31 bytes: https://devzone.nordicsemi.com/f/nordic-q-a/31317/ble-advertising-max-size-does-it-include-manufacturer-specific-data

However, If you use extended advertising you will be able to advertise more data.

Best regards,

Simon

[zciwor]

Simon, can you point me towards documentation that describes the sd and ad arrays in detail? 

[Simon]

I could not find any NCS/Zephyr specific guides that explains these arrays in details. However, the payload data in the advertising packet is structured in the following manner

| Length | AD Type | AD Data | Length | AD Type | AD Data | Length | AD Type | AD Data ...

Where "Length" occupies one byte, "AD Type" occupies 1 byte and AD Data occupies one or more bytes (specified by "Length").

If you capture a sniffer trace of the advertising packet, this is what you will see inside the payload

Each bt_data struct you add to the sd/ad array will get merged together and get transformed into the above structure.

The macros BT_DATA_BYTES(..) and BT_DATA(..) are just used to simplify the process of creating bt_data structs,

Best regards,

Simon

[STE]

Dear Simon,

I find this very useful, but what happen if I've more custom service inside my device? It's UUID may do not fit inside the payload...

Thanks and best regards.