CCS/CC2640R2F: MTU negotiation request on peripheral side

Hi Trevor,

The GAP Peripheral/Central roles are independent of GATT Client/Server. Central/Peripheral can act as both Client and/or Server. TI supports all combinations.

Trevor,

Per the BT5.1 core specification; "The Exchange MTU Request is used by the client to inform the server of the client’s maximum receive MTU size and request the server to respond with its maximum receive MTU size"

This means that the simple peripheral must also define itself as a GATT Client as well as a GATT Server. To do this, please see the SimpleCentral_init function of the simple central sample app;

  // Initialize GATT Client
  VOID GATT_InitClient();

Then you need to add all necessary application code to handle Client operation (again take inspiration of simple central). After that, you should be able to execute this api (gatt.h);

/*-------------------------------------------------------------------
 * GATT Client Sub-Procedure APIs
 */

/**
 * @brief   Exchange MTU Request
 *
 * This sub-procedure is used by the client to set the ATT_MTU
 * to the maximum possible value that can be supported by both
 * devices when the client supports a value greater than the
 * default ATT_MTU for the Attribute Protocol. This sub-procedure
 * shall only be initiated once during a connection.
 *
 * @ref ATT_ExchangeMTUReq is used by this sub-procedure.
 *
 * @par Corresponding Events:
 * If the return status from this function is @ref SUCCESS, the calling
 * application task will receive a @ref GATT_MSG_EVENT message with method:
 * - @ref ATT_EXCHANGE_MTU_RSP of type @ref attExchangeMTURsp_t , with
 * status @ref SUCCESS or @ref bleTimeout , if the procedure was successful
 * - @ref ATT_ERROR_RSP of type @ref attErrorRsp_t , with
 * status @ref SUCCESS  , if an error occurred on the server
 *
 * @param   connHandle - connection to use
 * @param   pReq - pointer to request to be sent
 * @param   taskId - task to be notified of response
 *
 * @return  @ref SUCCESS : Request was queued successfully.
 * @return  @ref INVALIDPARAMETER
 * @return  @ref MSG_BUFFER_NOT_AVAIL
 * @return  @ref bleNotConnected
 * @return  @ref blePending : A response is pending with this server.
 * @return  @ref bleMemAllocError
 * @return  @ref bleTimeout : Previous transaction timed out.
 */
extern bStatus_t GATT_ExchangeMTU( uint16 connHandle, attExchangeMTUReq_t *pReq, uint8 taskId );