Detect MTU and Interval during connection?

RE: Detect MTU and Interval during connection?

mrono — Mon, 30 Jul 2018 08:48:34 GMT

The GATT module has the nrf_ble_gatt_link_t -struct. And a getter function nrf_ble_gatt_eff_mtu_get().

If you are already using the gatt module, I'd assume this would be the way to get the MTU size rather than assuming or having the application also keep track of update events.

RE: Detect MTU and Interval during connection?

Håkon Alseth — Mon, 30 Jul 2018 07:50:09 GMT

You're right. The MTU is 23 (20 bytes of user-data) by default, unless the ATT_MTU is updated on-air.

RE: Detect MTU and Interval during connection?

SRA — Fri, 27 Jul 2018 20:15:22 GMT

Håkon, great, that works if there is a re-negotiation but we're still not clear on how to pick up the MTU at initial connection... or is it always default (20ish) and has to run through the update to make it longer?

RE: Detect MTU and Interval during connection?

Håkon Alseth — Fri, 27 Jul 2018 12:18:54 GMT

In example ble_app_hrs (and many others), this is reported via the nrf_ble_gatt module:

/**@brief GATT module event handler.
 */
static void gatt_evt_handler(nrf_ble_gatt_t * p_gatt, nrf_ble_gatt_evt_t const * p_evt)
{
    if (p_evt->evt_id == NRF_BLE_GATT_EVT_ATT_MTU_UPDATED)
    {
        NRF_LOG_INFO("GATT ATT MTU on connection 0x%x changed to %d.",
                     p_evt->conn_handle,
                     p_evt->params.att_mtu_effective);
    }

    ble_hrs_on_gatt_evt(&m_hrs, p_evt);
}


/**@brief Function for initializing the GATT module.
 */
static void gatt_init(void)
{
    ret_code_t err_code = nrf_ble_gatt_init(&m_gatt, gatt_evt_handler);
    APP_ERROR_CHECK(err_code);
}

Best regards,

Håkon

RE: Detect MTU and Interval during connection?

SRA — Wed, 25 Jul 2018 17:09:37 GMT

Would you mind showing WHERE they are available? "In the event" doesn't entirely point me to the structure they are available in. Any example code by chance?

RE: Detect MTU and Interval during connection?

RK — Wed, 25 Jul 2018 02:05:31 GMT

and the other connection parameters are in the original connection event and the connection parameter update events.

RE: Detect MTU and Interval during connection?

RK — Wed, 25 Jul 2018 01:39:20 GMT

All these data length parameters come in the BLE_GAP_EVENT_DATA_LENGTH_UPDATE events. You can start by assuming any connection has the default and then, if you get one of those events after the procedure has been performed, update the value.