RTOS/LAUNCHXL-CC2650: BLE central device, GATT_DiscCharsByUUID()

Tom Victor

Part Number: LAUNCHXL-CC2650
Other Parts Discussed in Thread: CC2650

Tool/software: TI-RTOS

Hello,

I am working on a product prototyping on CC2650 launchpad with the simple central (from simple-link GitHub) as the starting point for the application.

I would like to read and write the characteristics value of another CC2650 launchpad running on simple peripheral. After reading the user guide I replace my code in the

buttoncb function ( SimpleBLECentral_handleKeys() ). on building the code it is throwing lot of errors.

can I use the GATT_DiscCharsByUUID() function directly before discovering service?

GATT_DiscCharsByUUID( uint16 connHandle, attReadByTypeReq_t *pReq, uint8 taskId )

Also what is the taskid parameter and pReq? any implementation example available?

where could I get support on this?

Thank you

Regards,

Tom Victor
CTO, Technorip Innovations pvt Ltd

over 8 years ago

0 Marie H over 8 years ago

TI__Guru* 82841 points

Hi Tom,

You need the start and end handles of the service to use GATT_DiscCharsByUUID(), so you will have to do a GATT_DiscPrimaryServiceByUUID() first. Also when you have done GATT_DiscPrimaryServiceByUUID() you don't have to discover the charcteristics since they are part of the service. In simple_central, look at SimpleBLECentral_processGATTDiscEvent() where simple profile is discovered, then characteristic 1 is read.

You can read more about the exchange of requests (attReadByTypeReq_t) and the GATT events containing the response (ATT_FIND_BY_TYPE_VALUE_RSP, ATT_READ_BY_TYPE_RSP and ATT_ERROR_RSP) in the BLE core spec. ( www.bluetooth.com/.../adopted-specifications )

The pReq should be a pointer to a attReadByTypeReq_t struct and the taskId is the task you want to be notified of the response. If you use selfEntity, the response can be fetched as a pMsg from SimpleBLECentral_processGATTDiscEvent().

0 Tom Victor over 8 years ago in reply to Marie H

Intellectual 345 points

Thank you Marie,

I have few more doubts,

In my case, BLE service is designed using Bluetooth developer studio, so I can directly use the known UUIDs on GATT_DiscPrimaryServiceByUUID() (assuming task id is selfEntity)right?

Where should I process the response, in the SimpleBLECentral_processStackMsg() function. Which event should I switched?

static void SimpleBLECentral_processStackMsg(ICall_Hdr *pMsg)
{
  switch (pMsg->event)
  {
    case GAP_MSG_EVENT:
      SimpleBLECentral_processRoleEvent((gapCentralRoleEvent_t *)pMsg);
      break;

    case GATT_MSG_EVENT:
      SimpleBLECentral_processGATTMsg((gattMsgEvent_t *)pMsg);
      break;

    case HCI_GAP_EVENT_EVENT:
      {
        // Process HCI message
        switch(pMsg->status)
        {
          case HCI_COMMAND_COMPLETE_EVENT_CODE:
            SimpleBLECentral_processCmdCompleteEvt((hciEvt_CmdComplete_t *)pMsg);
            break;

          default:
            break;
        }
      }
      break;

    default:
      break;
  }
}

Thank you

Regards,

Tom Victor

0 Marie H over 8 years ago in reply to Tom Victor

TI__Guru* 82841 points

Hi Tom,

Unless you have specified that your service should be a secondary service (and not a primary service which is the default), you can use GATT_DiscPrimaryServiceByUUID().

SimpleBLECentral_processStackMsg() will sort the events for you. GATT_DiscPrimaryServiceByUUID() will return a GATT_MSG_EVENT, so you should go to SimpleBLECentral_processGATTMsg().

If you want, you can take the code already in place in simple central to discover Simple Service and replace its UUIDs with you own. Again, please take a look at the BLE Core spec ( www.bluetooth.com/.../adopted-specifications ), chapter 4.4.2 Discover Primary Service by Service UUID!

0 Tom Victor over 8 years ago in reply to Marie H

Intellectual 345 points

Dear Marie,

Thank you for the information.

I just gone through the guides and program, I got few doubts !

In the SimpleBLECentral_processGATTDiscEvent() function, I want to read the characteristics value (defined by GATT_ReadUsingCharUUID() function) . I am able to enter into the if condition(code below) and print the the display code. But I cant understand the correct data pointer holding the characteristic value, from the att.h file.

else if (discState == BLE_DISC_STATE_CHAR)
    {
        // Characteristic found, store handle
        if ((pMsg->method == ATT_READ_BY_TYPE_RSP) &&
            (pMsg->msg.readByTypeRsp.numPairs > 0))
        {
            charHdl = BUILD_UINT16(pMsg->msg.readByTypeRsp.pDataList[0],
                                   pMsg->msg.readByTypeRsp.pDataList[1]);
            Display_print0(dispHandle, ROW_THREE, 0, "Simple Svc Found");
            procedureInProgress = FALSE;
        }
        discState = BLE_DISC_STATE_IDLE;
    }

I hope "attMsg_t" is the data structure holding the response pointers?

can I use the following method

for(i=0; i< pMsg->msg.readRsp.len; i++){
                response[i] = pMsg->msg.readRsp.pValue ;
            }

Thank you Marie

Regards,

Tom Victor

0 Marie H over 8 years ago in reply to Tom Victor

TI__Guru* 82841 points

Hi Tom,

Quoting the core spec: "Read By Type Response returns a list of Attribute Handle and Attribute Value pairs[...]", meaning that DataList also contains the attribute values. So if you want to see the value of the attribute you have too look at pDataList[2] etc. for all the attributes belonging to the characteristic.

Alternatively you can send a read request using the characteristic handle obtained from GATT_ReadUsingCharUUID(). There is an example of this in simple central under SimpleBLECentral_handleKeys, case MENU_ITEM_READ_WRITE:

				  				// Do a read
				  				attReadReq_t req;
				  				req.handle = charHdl;
				  				status = GATT_ReadCharValue(connHandle, &req, selfEntity);
				  				Display_print0(dispHandle, ROW_SIX, 0, "Read req sent");

The reply comes in SimpleBLECentral_processGATTMsg(), ATT_READ_RSP:

if (pMsg->method == ATT_ERROR_RSP)
			{
				Display_print1(dispHandle, ROW_SIX, 0, "Read Error %d", pMsg->msg.errorRsp.errCode);
			}
else
			{
				// After a successful read, display the read value
				Display_print1(dispHandle, ROW_SIX, 0, "Read rsp: %d", pMsg->msg.readRsp.pValue[0]);
			}

PS. I'm aware that this is super confusing, but we will get there! :)

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RTOS/LAUNCHXL-CC2650: BLE central device, GATT_DiscCharsByUUID()