What exactly does sd_ble_gatts_characteristic_add do?

[Mitch996]

My guess is that:

Characteristics are (or at least, can be considered) subsets of services, which in turn, are (or at least, can be considered) subsets of profiles.

The BLE standard gave developers a lot of latitude which enables them to customize services and profiles, which means developers can add or "not add" characteristics, which are core components of services.

My questions:

1. Is my above understanding correct?
2. What happens if I want to add some "default" characteristics? I'm thinking either one of the following 3 possiblities will be the case:

A. you don't have to, certain characteristics must come with a service anyway, or the service will be invalid;

B.There are default, liberary functions for that and all you have to do is to call these "specialized" functions and that will be that

C. you still have to add them like you add your own, customized characteristics, it's just that all the parameteres needed when adding the default characteristics are fixed and designated in the library and cannot be modified.

Please help, thanks in advance.

[Petter Myhre]

1. Correct.
2. Default? Do you mean profiles/services adopted by the Bluetooth SIG? Then you need to implement the profile, service, characteristic, descriptors according to the specifications. The SoftDevice will not do this for you, sd_ble_gatts_characteristic_add() will not check if you are adding the characteristic to the appropriate service. We have examples that show how to implement many of these profiles, for example the Heart Rate Profile.

[AmiguelS]

Your understanding is correct. The basic building block of BLE are Attributes, which are then grouped into Characteristic, Services and Profiles. This image may make the concept clearer.

There are indeed default characteristics, services and profiles, but the SoftDevice does not implement them for you. If you which to support a default service, you must read its specification and manually implement it on your device. The advantage of default Services and Profiles is that other devices will be compatible with your implementation, since you used a publicly available and agreed upon set of attributes and UUIDs.

If you whish, you can implement your own Profile that contains several Services from multiple standard profiles. You may even add your own services on top of this.

[AmiguelS]

If you have obtained the information you were seeking from one of the answers bellow, could you please mark one as accepted?

[Mitch996]

Hello, this is a bit embarrassing but I searched through the page entirely yet failed to find the "accept" button?

[Petter Myhre]

The answer is accepted by clicking the green check mark next to it.