A few questions about GATT

[Mitch996]

As I came to understand, all the services & characteristics are registered in a "GATT table" of some sort, so my question:

1. What are the functions used to create and subsequently maintain this table? I can't find the relevant struct, which is strange because if there is a attribute/property table of some sort, I usually need to configure "it", which usually is a struct.

2. Are there "default" services? By that I mean services that comes with a GATT connection, something which you don't have to declare explicitly using any function. I ask this because I have a program that invoke sd_ble_gatts_service_add once, yet I can view 3 on my android device, 2 of which (the ones that weren't "intentionally" created by me) start with UUID 0000 1800.

3. If I want to read or write to certain characteristics, I need to first enable them. It can be done on both central & peripheral devices, right?

[Sigurd]

Hi,

1) The GATT table is a part of the SoftDevice, and the application can use the API functions sd_ble_gatts_* to interact with the GATT. You can find the GATT SoftDevice functions here.

2) Yes, there are always 2 mandatory services:

1. The Generic Access service with UUID 0x1800, which contains general information about the device.
2. The Generic Attribute service with UUID 0x1801, used to notify the central of changes in the services and characteristics on the peripheral.

3) If you want to read/write to a characteristics you need to add read/write properties and permissions to the characteristics. You can find more information in e.g. the BLE Characteristics tutorial.