For the BLE_DataThroughput example, in dts.c, when receiving an event of EVT_BLUE_GATT_ATTRIBUTE_MODIFIED and trying to find out which characteristic is the one being modified, why do the handles have an integer added to them prior to the comparison?

[Patrick Chwalek]

The code in question is below. You can see that each of the characteristic handles have an integer added to them prior to the comparison (i.e., + 2, + 5, +1). Why?

 case EVT_BLUE_GATT_ATTRIBUTE_MODIFIED:
        {
          attribute_modified = (aci_gatt_attribute_modified_event_rp0*) blue_evt->data;
          if (attribute_modified->Attr_Handle == (aDataTransferContext.DataTransferTxCharHdle + 2))
          {
            /**
             * Notify to application to start measurement
             */
            if (attribute_modified->Attr_Data[0] & DTS_STM_NOTIFICATION_MASK)
            {
              APP_DBG_MSG("notification enabled\n");
              Notification.Evt_Opcode = DTS_STM__NOTIFICATION_ENABLED;
              DTS_Notification(&Notification);
            }
            else
            {
              APP_DBG_MSG("notification disabled\n");
              Notification.Evt_Opcode = DTS_STM_NOTIFICATION_DISABLED;
              DTS_Notification(&Notification);
            }
          }
          //if (attribute_modified->Attr_Handle == (aDataTransferContext.DataTransferTxChar3Hdle + 2))
          if (attribute_modified->Attr_Handle == (aDataTransferContext.DataTransferTxChar3Hdle + 5))
          {
            /**
            * Notify to application to start measurement
            */
            if (attribute_modified->Attr_Data[0] & DTS_STM_NOTIFICATION_MASK)
            {
              APP_DBG_MSG("notification enabled\n");
              Notification.Evt_Opcode = DTC_NOTIFICATION_ENABLED;
              DTS_Notification(&Notification);
            }
            else
            {
              APP_DBG_MSG("notification disabled\n");
              Notification.Evt_Opcode = DTC_NOTIFICATION_DISABLED;
              DTS_Notification(&Notification);
            }
          }
          if(attribute_modified->Attr_Handle == (aDataTransferContext.DataTransferRxCharHdle + 1))
          {
            return_value = SVCCTL_EvtAckFlowEnable;
            
            Notification.Evt_Opcode = DTS_STM_DATA_RECEIVED;
            Notification.DataTransfered.Length=attribute_modified->Attr_Data_Length;
            DTS_Notification(&Notification); 
          }
          }
          break;
        case EVT_BLUE_GATT_TX_POOL_AVAILABLE:
          Resume_Notification();
          break; 
          
      case EVT_BLUE_GATT_WRITE_PERMIT_REQ:
        APP_DBG_MSG("write permit req\r\n");
        write_permit_req = (aci_gatt_write_permit_req_event_rp0 *) blue_evt->data;
        aci_gatt_write_resp( write_permit_req->Connection_Handle, write_permit_req->Attribute_Handle, 0, 0, write_permit_req->Data_Length, write_permit_req->Data);        
        break;

[mkrug]

Hi Patrick,

I actually have the same question that you raised. So why is a value added to the handle before the comparision? Did you receive an answer?

Best Regards

Markus

[Patrick Chwalek]

Unfortunately, I have not-- I still don't understand why that's done.

[Targo]

Hi @Patrick Chwalek​ and @Community member​,

Have either of you managed to find an answer yet? Or any reference to what integers need to be added in any documentation?

Best Regards,

Targo

[Patrick Chwalek]

Hi @Targo​ , I have not found an answer. My solution to this is a bit brute force.

1. Setup all the characteristics for the service
2. Connect to service via secondary device
3. Send data to specific characteristics
4. Add a breakpoint in the handler for that service
5. Check the value of attribute_modified->Attr_Handle and then hardcode the if statement with the correct offset

[Targo]

Hi @Patrick Chwalek​ , thank you. I guess I will have to do the same.

In the latest version of "ble_gatt_aci.h" above the function "aci_gatt_add_char" I did see this:

"

The command returns the handle of the declaration attribute. The attribute

 * that holds the Characteristic Value is always allocated at the next handle

 * (Char_Handle + 1). The Characteristic Value is immediately followed, in

 * order, by:

 * - the Server Characteristic Configuration descriptor if CHAR_PROP_BROADCAST

 * is selected;

 * - the Client Characteristic Configuration descriptor if CHAR_PROP_NOTIFY or

 * CHAR_PROP_INDICATE properties is selected;

 * - the Characteristic Extended Properties descriptor if CHAR_PROP_EXT is

 * selected.

 * For instance, if CHAR_PROP_NOTIFY is selected but not CHAR_PROP_BROADCAST

 * nor CHAR_PROP_EXT, then the Client Characteristic Configuration attribute

 * handle is Char_Handle + 2.

"

Although I don't fully understand it.

[Patrick Chwalek]

So the thought here is that the offset depends on the attribute with which the characteristic is set? I have yet to try modifying the attributes and checking the offset.