[S132] CCCD value not being initialized

[planas]

Hi, I wrote a custom service with a characteristics with notifications support. After a client connects I start the sensors and I start updating the values. On the service I'm using the sd_ble_gatts_hvx function to update the value and send a notification in case it is enabled.

In theory the function should return NRF_ERROR_STATE_INVALID when the notifications are not enabled, but instead I'm getting a BLE_ERROR_GATTS_SYS_ATTR_MISSING. But if I write a 0 to the CCCD it starts reporting NRF_ERROR_STATE_INVALID which is the expected error.

I assume this is issue is due to the SD not initializing the CCCD to 0. I am right?

Thanks

[Susheel Nuguru]

Hi,

Your assumption is correct, but this is not a bug. Atleast not a implementation bug. nothing is initialized to 0 inside sd_ble_gatts_characteristic_add. It is upto application to do this. This probably could have been documented. If you see any example (like ble_app_uart) you will see that all metadata and attribute descriptors are memset to 0 by the app.

[planas]

Hi Aryan, I'm initializing all the structs to zero, but which struct contains the initial CCCD value? I thought this was managed by the SD. I mean, you can initialize the char value through ble_gatts_attr_t, and you can set the permissions, mem location, etc. of the CCCD through the ble_gatts_attr_md_t metadata struct, but I don't see how I should initialize the CCCD value which theoretically should be 0. Just in case, this is my implementation http://pastebin.com/g1G3bCK6

[Susheel Nuguru]

That is interesting, can you please post the code snippet of how you write to CCCD?

[planas]

AFAIK there's not a function to write directly to the CCCD on the SDK, so I'm writing to it through the device acting as central, eg. the MCP.

[Susheel Nuguru]

You were right about not initializing CCCD, but it is not a bug. CCCDs are not initialized in memory because their values are persistent. The application can tell the softdevice what values it should store in CCCD using sd_ble_gatts_sys_attr_set. If the app doesn't have stored values for CCCDs (system attributes) for a particular peer, then it can send sd_ble_gatts_sys_attr_set(conn_handle, NULL, 0) and softdevice should reset the CCCD values to 0.