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

[Marcel Mulder]

But this does not solve my problem. The only answer I get is use 8.0.0 but as I mentioned this is currently not an option. Leaves the unanswered questions:

1. Why is the data returned from sd_ble_gatts_sys_attr_get so huge?
2. As you mention I am still allowed to get them one by one. How?

Another remark: Per spec the CCCD's are persistent, I know, but why is then everybody using sd_ble_gatts_sys_attr_set(conn_handle, NULL, 0)? Including the Nordic examples? I worked with CSR also here is does not happen.

Marcel