nRF51822 s110 - How to determine if Notification and/or Indication for each characteristic is switched on or not by the central

Question

Using S110 version 6.0.0, Sdk 5.2.0, GCC 4.8 (C++, but that don't matters here).

I want to know, if the central has switched Notification and/or Indication on or off for a specific characteristic.

As seen in the experimental nRF Uart example code, I could hear on BLE_GATTS_EVT_WRITE and then call ble_srv_is_notification_enabled() / ble_srv_is_indication_enabled(), like this:

void BleNts::onWrite(const ble_evt_t& bleEvt) {
    // TODO: Should I also check bleEvt.evt.gatts_evt.conn_handle==connHandle ?
    const ble_gatts_evt_write_t& evtWrite = bleEvt.evt.gatts_evt.params.write;
    auto handle = evtWrite.handle;
    if (evtWrite.handle == handles.cccd_handle and evtWrite.len == 2) {
        bool notificationEnabled = ble_srv_is_notification_enabled(const_cast<uint8_t*>(evtWrite.data));
        bool indicationEnabled = ble_srv_is_indication_enabled(const_cast<uint8_t*>(evtWrite.data));
        LOG_DEBUG("notification=%d indication=%d", notificationEnabled, indicationEnabled);
    }
}

But this fails e.g. for the following szenario:

Central has switched both Notification and Indication on
Central now swiched Notification off (while leaving Indication switched on)
in this case, the above code thinks that both Notification and Indication should switched off

I'd made a bit debug output inside of my void BleNts::onBleEvt(const ble_evt_t& bleEvt) and see the following (using nRF Mcp as Central side to switch notification/indication on/off):

// Starting with both notification and indication switched off
// Step 1: At first switching notification on
Ble event id=50h len=34, name=GATTS_EVT_WRITE, range=Gatt server event
  conn_handle=0
  Write: handle=15, op=1, offset=0, len=2, data=01 00
  Context: srvc_uuid=0001/2, char_uuid=0004/2, desc_uuid=2902/1, srvc_handle=12, value_handle=14, type=6
BleNts notification=1 indication=0

// Step 2: Now also switching indication on
Ble event id=50h len=34, name=GATTS_EVT_WRITE, range=Gatt server event
  conn_handle=0
  Write: handle=15, op=1, offset=0, len=2, data=02 00
  Context: srvc_uuid=0001/2, char_uuid=0004/2, desc_uuid=2902/1, srvc_handle=12, value_handle=14, type=6
BleNts notification=0 indication=1
// ... wrong result ...

// Step 3: Now switching notification off
Ble event id=50h len=34, name=GATTS_EVT_WRITE, range=Gatt server event
  conn_handle=0
  Write: handle=15, op=1, offset=0, len=2, data=00 00
  Context: srvc_uuid=0001/2, char_uuid=0004/2, desc_uuid=2902/1, srvc_handle=12, value_handle=14, type=6
BleNts notification=0 indication=0
// ... wrong result ...

// Step 4: Finally switching also indication off
Ble event id=50h len=34, name=GATTS_EVT_WRITE, range=Gatt server event
  conn_handle=0
  Write: handle=15, op=1, offset=0, len=2, data=00 00
  Context: srvc_uuid=0001/2, char_uuid=0004/2, desc_uuid=2902/1, srvc_handle=12, value_handle=14, type=6
BleNts notification=0 indication=0

Within my debug output, I see no difference between step 3 and step 4; both contains "data=00 00".

Seems that I better should ask something from inside the S110 instead of evaluate the received data, isn't it?

Any suggestion about that?

Joe Merten · Accepted Answer

Ok, after looking a bit deeper behind the surface, the facts are clear. 
 Shure, it mostly make no sense to activate both notification and indication for the same characteristic (although e.g. the Android Ble interface BluetoothGattDescriptor has values for switching of the one or the other but not for both on). 
 In the case of my tiny test ble application (running on nRF51822 / S110), I'd allowed both notification and indication for the same characteristic. While testing that using nRF Mcp (on Android), the bug is on the central's (Mcp) side . 
 The nRF Mcp UI provides the possibility to switch both notification and indication on / off independently from each other, but it isn't so. 
 As Pål Håland already wrote, when in step 2 indication is switched on (after notification was switched on before), the central had to send "03 00" instead of "02 00".

nRF51822 s110 - How to determine if Notification and/or Indication for each characteristic is switched on or not by the central

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