I cannot read a BLE characteristic on Bluetooth 5.0 but on Bluetooth 5.1 it work

[AMuya.1]

Good day to all,
I'm having an issue with a BLE characteristic on the STM32WB55. I have a characteristic that is a read only (it doesn't notify or indicate), and currently, it is just a counter that increments every second. I'm running a P2Pserver, with 1 service and 3 characteristics.
When I read the characteristic with a client application on my desktop with BLE 5.1 it works (I also used my phone with BLE 5.1 and it also works).
When I try to read on my laptop with a BLE 5.0, it will only read the characteristic when the Bluetooth connects but after that doing a read doesn't work at all.

The only thing different is the Bluetooth version of my devices. Other than that I don't know what could be the cause.
If anyone has an idea on how to fix this issue please help, because I expect this simple application to be backward compatible to BLE 4.2.

I am using the most recent version of STM32cube and the most recent firmware package for my board.

Here is how I initialized the characteristic

  /**
   *  P2P_State
   */
  COPY_P2P_STATE_UUID(uuid16.Char_UUID_128);
  ret = aci_gatt_add_char(aPeerToPeerContext.PeerToPeerSvcHdle,
                          UUID_TYPE_128, &uuid16,
                          0x02,
                          CHAR_PROP_READ,
                          ATTR_PERMISSION_NONE,
                          GATT_NOTIFY_READ_REQ_AND_WAIT_FOR_APPL_RESP,
                          0x10,
                          CHAR_VALUE_LEN_CONSTANT,
                          &(aPeerToPeerContext.P2PCommsStateHdle));
  if (ret != BLE_STATUS_SUCCESS)
  {
    APP_DBG_MSG("  Fail   : aci_gatt_add_char command   : P2PCOMMSSTATE, error code: 0x%x \n\r", ret);
  }
  else
  {
    APP_DBG_MSG("  Success: aci_gatt_add_char command   : P2PCOMMSSTATE \n\r");
  }

The function P2PS_UpdateCounter() is called in main every 1 seconds.
and P2PS_STM_App_Update_Char(....), update the characteristics value. this function doesn't fail and finish succesffuly. 

void P2PS_UpdateCounter( void )
{
  static uint16_t ucMoreTimeCounter = 0;

  ucMoreTimeCounter++;

  if( P2P_Server_App_Context.Notification_Status )
	{
    P2PS_STM_App_Update_Char( P2P_STATE_CHAR_UUID, &ucMoreTimeCounter, 2 );
	}

  return;
}

tBleStatus P2PS_STM_App_Update_Char( uint16_t UUID, uint8_t *pPayload, uint16_t usLength )
{
  tBleStatus result = BLE_STATUS_INVALID_PARAMS;
  switch(UUID)
  {
    case P2P_STATE_CHAR_UUID:
      result = aci_gatt_update_char_value(aPeerToPeerContext.PeerToPeerSvcHdle,
                                      aPeerToPeerContext.P2PCommsStateHdle,
                                      0, /* charValOffset */
                                      usLength, /* charValueLen */
                                      (uint8_t *)  pPayload);
      if (result != BLE_STATUS_SUCCESS)
      {
        APP_DBG_MSG("  Fail   : aci_gatt_update_char_value STATE command, result : 0x%x \n\r", result);
        // printf("  Fail   : aci_gatt_update_char_value STATE command, result : 0x%x \n\r", result);
      }
      else
      {
        APP_DBG_MSG("  Success: aci_gatt_update_char_value STATE command\n\r");
        // printf("  Success: aci_gatt_update_char_value STATE command\n\r");
      }
      break;

    default:
      break;
  }

  return result;
}/* end P2PS_STM_Init() */

And finally, In the function that handle ACI_GATT events below, on BLE5.1 when I do a read on the characteristic, I can see that the event ACI_GATT_READ_PERMIT_REQ_VSEVT_CODE  every single time I do a read but on BLE 5.0, this event doesn't get triggered. it only triggered when a client connects. 

static SVCCTL_EvtAckStatus_t PeerToPeer_Event_Handler(void *Event)
{
  SVCCTL_EvtAckStatus_t return_value;
  hci_event_pckt *event_pckt;
  evt_blecore_aci *blecore_evt;
  aci_gatt_attribute_modified_event_rp0    * attribute_modified;
  aci_gatt_read_permit_req_event_rp0       *read_req;
  aci_gatt_notification_complete_event_rp0 *notification_complete;

  P2PS_STM_App_Notification_evt_t Notification;

  return_value = SVCCTL_EvtNotAck;
  event_pckt = (hci_event_pckt *)(((hci_uart_pckt*)Event)->data);

  switch(event_pckt->evt)
  {
    case HCI_VENDOR_SPECIFIC_DEBUG_EVT_CODE:
    {
      blecore_evt = (evt_blecore_aci*)event_pckt->data;
      switch(blecore_evt->ecode)
      {
        case ACI_GATT_ATTRIBUTE_MODIFIED_VSEVT_CODE:
        {
          ............
        }
        break;

        case ACI_GATT_READ_PERMIT_REQ_VSEVT_CODE :
          /* USER CODE BEGIN EVT_BLUE_GATT_READ_PERMIT_REQ_BEGIN */
          printf("BLE READ\n");
          /* USER CODE END EVT_BLUE_GATT_READ_PERMIT_REQ_BEGIN */
          read_req = (aci_gatt_read_permit_req_event_rp0*)blecore_evt->data;
          if (read_req->Attribute_Handle == (aPeerToPeerContext.P2PCommsStateHdle + 1))
          {
            return_value = SVCCTL_EvtAckFlowEnable;
            /*USER CODE BEGIN CUSTOM_STM_Service_1_Char_3_ACI_GATT_READ_PERMIT_REQ_VSEVT_CODE_1 */

            /*USER CODE END CUSTOM_STM_Service_1_Char_3_ACI_GATT_READ_PERMIT_REQ_VSEVT_CODE_1*/
            aci_gatt_allow_read(read_req->Connection_Handle);
            /*USER CODE BEGIN CUSTOM_STM_Service_1_Char_3_ACI_GATT_READ_PERMIT_REQ_VSEVT_CODE_2 */
            printf("BLE STATE\n");

            /*USER CODE END CUSTOM_STM_Service_1_Char_3_ACI_GATT_READ_PERMIT_REQ_VSEVT_CODE_2*/
          } /* if (read_req->Attribute_Handle == (aPeerToPeerContext.P2PCommsStateHdle + CHARACTERISTIC_VALUE_ATTRIBUTE_OFFSET))*/
          
          /* USER CODE BEGIN EVT_BLUE_GATT_READ_PERMIT_REQ_END */

          /* USER CODE END EVT_BLUE_GATT_READ_PERMIT_REQ_END */
          break;
      
        case ACI_GATT_NOTIFICATION_COMPLETE_VSEVT_CODE:
          {
            ...............
            break;
          }

      default:
        break;
      }
    }
    break; /* HCI_HCI_VENDOR_SPECIFIC_DEBUG_EVT_CODE_SPECIFIC */

    default:
      break;
  }

  return(return_value);
}/* end SVCCTL_EvtAckStatus_t */

[STTwo-32]

Hello @AMuya.1 

Could you please add your .ioc file. 

Best Regards.

STTwo-32