How to get full Service UUID from given BASE UUID

[davidm]

Hi all

I am trying to pair nrf52840 (as a central) with ESP32 (as peripheral).

 Now I want to get the service uuid so that i can pass to advertising service in ESP32 code.How do I get the full-service UUID, I see that in the ble_lbs_c service  UUID is declared as 0x1523 characteristic  UUID as 0x1525 and LBS_UUID_BASE {0x23, 0xD1, 0xBC, 0xEA, 0x5F, 0x78, 0x23, 0x15, 0xDE, 0xEF, 0x12, 0x12, 0x00, 0x00, 0x00, 0x00}

I tried to pass the service uuid as #define SERVICE_UUID   "23151212EFDE1523785FEABCD1" on ESP32 program but that didnt work. What is the exact order of the UUID? If you need  details on esp32 code here is the example esp32 program

I am using ble_app_blinky_c example on nrf52840.

Thank you in advance

[Edvin]

Hello,

I am not sure how the ESP libraries work, or how they set up their UUID. Have you tried looking at this device using nRF Connect? Whatever the outcome of the UUID is when you set it like that, you can compare it to the scanned UUID (if the ESP advertises using it's UUID at all). You can download the app version of nRF Connect on google play store or the iOS App Store. Alternatively, you can use the nRF Connect for Desktop (which requires an extra nRF DK/dongle).

[davidm]

Hi Edvin

Thank you for your quick response but I think there might be a misunderstanding. I am trying to find out, what the full-service UUID that will be formed by the Central(in this case Nrf52840) not ESP32.Once I get that I would use it , for advertising in ESP32 code.

Thank you again.

[Edvin]

If you look at the examples ble_app_uart and ble_app_uart_c from the SDK, these are examples that set and scan for a particular UUID. If you see in the ble_app_uart example iin the ble_nus.c the UUID is defined in NUS_BASE_UUID:

#define NUS_BASE_UUID                  {{0x9E, 0xCA, 0xDC, 0x24, 0x0E, 0xE5, 0xA9, 0xE0, 0x93, 0xF3, 0xA3, 0xB5, 0x00, 0x00, 0x40, 0x6E}} /**< Used vendor specific UUID. */

Note that when you scan for it, the order is byte reversed:

Also note that the 0x00, 0x00 are changed with the 2 byte UUID for the service, which is 0x0001.

If you look for the ble_app_uart_c example's UUID definition:

#define NUS_BASE_UUID                   {{0x9E, 0xCA, 0xDC, 0x24, 0x0E, 0xE5, 0xA9, 0xE0, 0x93, 0xF3, 0xA3, 0xB5, 0x00, 0x00, 0x40, 0x6E}} /**< Used vendor specific UUID. */

(identical to the ble_app_uart UUID).

So if you look at these examples, and compare the UUID that the central (ble_app_uart_c) looks for, and how the UUID looks like in the nRF Connect for Mobile app, then you can figure out what the UUID in your central should look like if you compare it to the UUID that the device advertise with in nRF Connect.

BR,
Edvin

[davidm]

Hi Edvin

Sorry for the delayed response. Thank you for your response above, I was able to track it down the service UUID (which on nrfconnect appears as 00001523-1212-EFDE-1523-785FEABCD123).So I used this service UUID  on esp32 (peripheral)  and  i can see it advertising but for some reason in the central(nrf52840) is not able to connect to it. How can I debug this in the central(nrf52840) board ?

[Edvin]

What SDK version are you using? I am asking because the scanning implementation was changed somewhere around 15.0.0 and 15.3.0, so depending on which one you use, it will be a bit different.

What you want to look for is the event BLE_GAP_EVT_ADV_REPORT which is called every time the scanner picks up an advertisement. In the older SDKs, this event is in main.c, but in the later SDKs, this is moved to a file called nrf_ble_scan.c.

It does some checks, based on your setup, and checks for either a UUID, an advertising name, or possibly an address. What does it look like in your case?

Typically, based on this check, it will decide whether to call sd_ble_gap_connect() or to continue to scan in the end. Does it ever call sd_ble_gap_connect() in your case?

BR,

Edvin