Handling BLE_ERROR_GATTS_SYS_ATTR_MISSING

[Hieu]

I am doing some test with the Battery Service on SDK v10, and found out that if I have not enabled Notification on my phone, calling ble_bas_battery_level_update() returns BLE_ERROR_GATTS_SYS_ATTR_MISSING, which originated from a call to sd_ble_gatts_hvx().

I have read this question linked here, where they say that it should be OK by just having sd_ble_gatts_sys_attr_set() called when receiving BLE_GATTS_EVT_SYS_ATTR_MISSING. The way I understand that answer, the SoftDevice would trigger the event BLE_GATTS_EVT_SYS_ATTR_MISSING and sd_ble_gatts_sys_attr_set() would set up System Attribute to avoid future issues.

However, even when I have the same code in my application, but I still encounter this error when the peer central has not enabled Notification. I have tested and seen the same error code 5 seconds after I received the first one. As a matter of fact, my tests show that I never receive the event BLE_GATTS_EVT_SYS_ATTR_MISSING.

1. Is this error code significant? Should I find a way to avoid this no matter what or is it OK to overlook it?

Update: I read the question linked above more and found that I could move sd_ble_gatts_sys_attr_set() to BLE_GAP_EVT_CONNECTED instead, and just stop caring about BLE_GATTS_EVT_SYS_ATTR_MISSING. But I am now interested in knowing why the original set up doesn't work.

2. How could I avoid this error code even when the peer device has not enable notification?

3. How does BLE_GATTS_EVT_SYS_ATTR_MISSING event have anything to do with this issue? Why did I never receive that event?

[Petter Myhre]

1. _
2. If the CCCD is actually set to 0x0000, you will not receive BLE_ERROR_GATTS_SYS_ATTR_MISSING, you will receive NRF_ERROR_INVALID_STATE.
3. As far as I know, you will only receive BLE_GATTS_EVT_SYS_ATTR_MISSING if the peer tries to read a CCCD that hasn't been set.