bt_gatt_notify issues

Question

I am developing a simple ble peripheral device that will measure temperature and humidity. For the most 
 part, it's working but I can't get the behavior I expect when enabling notifications. I have searched various 
 web sites - including Zephyr - for info; but am coming up short. Some help would be appreciated. 
 
 I am using latest nrf connect sdk to develop the app, I have been having problems consistently using 
 the vscode front-end, so I am currently using the nrf connect cli for building the app and nrf downloading 
 tool to flash. Will leave questions about vscode for another thread. I can reliably build and flash apps 
 using the above and am using the android nrf connect test app on smartphone for verifying correct 
 service behavior. Service declaration is as follows:

BT_GATT_SERVICE_DEFINE (svc, 
 BT_GATT_PRIMARY_SERVICE (BT_UUID_ESS), 
 
 BT_GATT_CHARACTERISTIC (BT_UUID_TEMPERATURE, 
 BT_GATT_CHRC_READ | BT_GATT_CHRC_NOTIFY, 
 BT_GATT_PERM_READ, 
 read_temperature, NULL , & temp_ble ), 
 
 BT_GATT_CCC (BLE_temperature_ccc_cfg_changed, 
 BT_GATT_PERM_READ | BT_GATT_PERM_WRITE), 
 
 BT_GATT_CHARACTERISTIC (BT_UUID_HUMIDITY, 
 BT_GATT_CHRC_READ | BT_GATT_CHRC_NOTIFY, 
 BT_GATT_PERM_READ, 
 read_humidity, NULL , & hum_ble ), 
 
 BT_GATT_CCC (BLE_humidity_ccc_cfg_changed, 
 BT_GATT_PERM_READ | BT_GATT_PERM_WRITE), 
 ); 
 
 temp_ble and hum_ble are updated from a SHT4x sensor over i2c using 
 existing Zephyr driver. Values are reasonable and that part appears to be 
 working reliably. I interrogate the sensor every 2 sec, and set both characteristic 
 values. After service discovery using android nrf connect tool, both can be read 
 out successfully. I also issue a bt_gatt_notify() for each value. It's my understanding 
 that, if a ble central node is connected AND notification has been enabled, then 
 these values will be reported to the client (i.e. ble central) and displayed. Here's 
 the main code: 
 
 ........ int bt_svc_set_temperature(int temp_ble) { int rc = bt_gatt_notify(NULL, &svc.attrs[1], &temp_ble, sizeof(temp_ble)); return rc == -ENOTCONN ? 0 : rc; } int bt_svc_set_humidity(int hum_ble) { int rc = bt_gatt_notify(NULL, &svc.attrs[3], &hum_ble, sizeof(hum_ble)); return rc == -ENOTCONN ? 0 : rc; } int main(void) { // start advertising int error = bt_enable(NULL); ........ error = bt_le_adv_start(BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad), NULL, 0); ......... printk("Advertising successfully started
"); while (1) { k_sleep(K_SECONDS(2)); if (sensor_sample_fetch(sht)) { printf("Failed to fetch sample from SHT4X device
"); } else { sensor_channel_get(sht, SENSOR_CHAN_AMBIENT_TEMP, &temp); temp_ble = temp.val1; // Only integer part of temp for now bt_svc_set_temperature(temp_ble); sensor_channel_get(sht, SENSOR_CHAN_HUMIDITY, &hum); hum_ble = hum.val1; // Only integer part of hum for now; bt_svc_set_humidity(hum_ble); } 
 
 As I mentioned, individual reads work fine. But notify's yield weird 
 behavors. In the above code, when temperature notifications are 
 enabled, it works correctly. When I subsequently enable humidity 
 notifications, the temperature value gets overwritten ( and contiinually 
 updated) with the humidity data. Humidity values do not get updated 
 at all. Various permutations of svc.attrs[x] 
 yield different - but also incorrect - behavior. 
 
 I clearly don't have the attrs[n] mapping to characteristics correct; but 
 can't find any discussion about it. So: 
 
 -What's the correct usage of svc.attrs[x] for the above service descriptor 
 macro. 
 
 -Do I need to wait for a notification to complete before issuing another? 
 If so, how can I detect completion? 
 
 Or, do I have the whole model of notification behavior wrong? 
 
 Thanks