Anthony Aubert

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5 years, 4 months ago.

requestMtu ?

Hello,

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

Javier Vargas
5 years, 2 months ago.

Hi.

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

Thank you.

Desmond Chen
5 years, 4 months ago.

Hi Anthony,

For configuring MTU size, there are two change needed.

mbed-os\features\FEATURE_BLE\targets\TARGET_CORDIO\stack\cordio_stack\ble-host\sources\stack\cfg\cfg_stack.c

/* 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 */
};

and

mbed-os\features\FEATURE_BLE\targets\TARGET_CORDIO\source\CordioBLE.cpp

void BLE::stack_setup()
{
    ...
    HciSetMaxRxAclLen(158);
    ...
}

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

- Desmond, team Mbed