I can't understand concept of control point..

[JoonDong]

I can't understand concept of control point..

Is it just one of charateristics?

So what are differences with other charateristics?

I heard that control point can be writable or notified, but cannot readable.

Is it right? I don't understand how unreadable value works.

[Petter Myhre]

A characteristic value could be a control point attribute, which per Bluetooth Core Specification 5.0, Vol 3, Part F, Section 3.2.6 is:

Attributes that cannot be read, but can only be written, notified or indicated arecalled control-point attributes. These control-point attributes can be used by higher layers to enable device specific procedures, for example the writing of a command or the indication when a given procedure on a device has completed.

You heard correct, and it is right.

Let me know if anything is still unclear.

[JoonDong]

Does it means that any data received using control point attribute handle is used promptly, not saved in attribute value? Then are these used in user code, for example in if statements?

[Petter Myhre]

Data received? Do you mean when a client writes to the attribute? Then the application on the server side will get a write event telling it that the attribute has been written to. Then it can react to the this event, but I guess it can also read it later. What is used in user code? I don't understand.

[JoonDong]

Yes, it is. If a server get a write event about control point when a client send it, does the server extract relevant data in ble_evt_t type p_ble_evt->gatts_evt.write.data[x], then use these data in <if/else statement> and so on.. to determine that whether to perform any codes, not save in control point attribute value?

[Petter Myhre]

Yes, the value will be saved.