not able to set system attributes using sd_ble_gatts_sys_attr_set

Question

Hello

I'm trying to reenable notifications on a characteristic from GATTS side

The device is 52810 running a custom service and this is the piece of code where i use

 err_code = sd_ble_gatts_sys_attr_get(m_service.conn_handle, 0, &attr_len, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS | BLE_GATTS_SYS_ATTR_FLAG_USR_SRVCS);
 err_code = sd_ble_gatts_sys_attr_get(m_service.conn_handle, sys_attr_data, &attr_len, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS | BLE_GATTS_SYS_ATTR_FLAG_USR_SRVCS);
      
      for(uint8_t i = 0; i < attr_len; i+= 6)
        {
        if(sys_attr_data[i] == iterator->value_handles.cccd_handle && sys_attr_data[i + 4] == 0)
          {
          sys_attr_data[i + 4] = 1;
          crc = crc16_compute(sys_attr_data, attr_len - 2, NULL);
          sys_attr_data[attr_len - 2] = crc & 0xff;
          sys_attr_data[attr_len - 1] = crc >> 8;
          err_code = sd_ble_gatts_sys_attr_set(m_service.conn_handle, sys_attr_data, attr_len, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS | BLE_GATTS_SYS_ATTR_FLAG_USR_SRVCS);    // initialize cccd attribute
          NRF_LOG_INFO("sys attr set: %2x / %2x %2x %2x", err_code, sys_attr_data[0], sys_attr_data[2], sys_attr_data[4]);
          memset(sys_attr_data, 0, 32);
          err_code = sd_ble_gatts_sys_attr_get(m_service.conn_handle, sys_attr_data, &attr_len, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS | BLE_GATTS_SYS_ATTR_FLAG_USR_SRVCS);
          NRF_LOG_INFO("sys attr get: %2x / %2x %2x %2x", err_code, sys_attr_data[0], sys_attr_data[2], sys_attr_data[4]);
          break;
          }
        }

log output is like this

[00:00:49.204,101] <info> app: sys attr set: 0 / E 2 1
[00:00:49.204,162] <info> app: sys attr get: 0 / E 2 0

The value set is 1 and the value get is 0, return value for both calls ...set() and ...get() is NRF_SUCCESS

can someone suggest how to set the value?

Sigurd · Accepted Answer

ves said: Can you give us some background for this behavior? 
 The intention is that it should not be possible to change the CCCDs locally/ on the GATT server. (other than the very first time on re-reconnect when you need to restore the values). It is the GATT client that enables and disables the CCCDs, the GATT server should not change these values locally, and get in a situation were there is a mismatch between what the value actually is, and what the GATT client believes the value is. The documentation is a big lacking on this point, so I will see if we can improve the documentation on this.

not able to set system attributes using sd_ble_gatts_sys_attr_set

Top Replies