1 year, 6 months ago.

requestMtu ?


I'am using the dev kit STM Discovery Node A1 (target DISCO_L475VG_IOT01A). I want to increase the Mtu but the reply is always 23...

Is it possible to increase Mtu size ?

D/RxBle#ConnectionOperationQueue: STARTED MtuRequestOperation(216468032) D/BluetoothGatt: configureMTU() - device: DE:32:43:33:0F:D3 mtu: 158 D/BluetoothGatt: onConfigureMTU() - Device=DE:32:43:33:0F:D3 mtu=23 status=0 D/RxBle#BluetoothGatt: onMtuChanged mtu=23 status=0 D/RxBle#ConnectionOperationQueue: FINISHED MtuRequestOperation(216468032) in 81 ms

Thanks a lot for your help.

2 Answers

1 year, 5 months ago.


How can I change it for the nRF52-DK device? And, how can I configure it using the mbed-app.json file?

Thank you.

1 year, 6 months ago.

Hi Anthony,

For configuring MTU size, there are two change needed.


/* Configuration structure */
attCfg_t attCfg =
  15,                               /* ATT server service discovery connection idle timeout in seconds */
  158,                  /* desired ATT MTU */
  ATT_MAX_TRANS_TIMEOUT,            /* transcation timeout in seconds */
  4                                 /* number of queued prepare writes supported by server */



void BLE::stack_setup()

With above two changes, you should be able to request MTU size=158.

- Desmond, team Mbed