CCCD and sd_ble_gatts_sys_attr_get

[Marcel Mulder]

I need to remember the CCCD's of some service, e.g. service changed. A CCCD is according to spec 2 bytes long. The method to do this is by using sd_ble_gatts_sys_attr_get. This function returns a binary blob which is not documented. The amount of data returned is, depending of how many characteristics you use, huge. Somewhere around 100 bytes. I don't want to store all this information for actually 1 bit, the indication config bit of service changed. Is there information available how this data is formatted? Or do I have to reverse engineer it?

Why is it implemented like this. Why not a function in the SD which can get or set the client characteristic configuration per handle? Or combine client and server characteristic configuration. This only has to return a 32 bits value.

Yes, I know there is BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS in SD v8 but going to SD v8 is not an option at the moment for my.

[Carles]

Hi there,

The reason we don't allow individually setting the CCCD values is that per the spec you need to remember all of them for a bonded device. You're still allowed to get them one by one though.

For the Service Changed user case as you already mentioned we have solved this in 8.0.0 by adding the new flags in the sys attr get and set functions.

Carles

[Carles]

1. Because you probably have a bunch of user CCCDs (i.e. characteristics that you have added that are either notifiable or indicatable or both), so those are all stored there along with the metadata that goes with them.
2. Use sd_ble_gatts_value_get() with the handle of the CCCD that interests you

I guess the examples you mention do not support bonding. CCCDs are only persistent if you are bonded with the device in question.

I will not comment about other implementations on the market, but we are open to suggestions to improve our own. I've created an internal ticket to consider allowing setting individual CCCDs by using sd_ble_gatts_value_set().