ESP32-S3 BLE connection not working after upgrade from 1.4.3 to 2.3.7

[bigrob3rto]

Good mornig,
I am working on a ESP32-S3 board and I use the Arduino Nimble library as CLIENT to connect to a third party device, a Valeton GP-5.
It works perfectly with the 1.4.3 library version.

It does not connect when upgrading to 2.3.7 version, I receive a:

E NimBLEClient: MTU exchange error; rc=2 Operation already in progress or complete
E NimBLEClient: Connection failed; status=2 Operation already in progress or complete  

and
Disconnected, reason = 534

Any idea what could be the problem with new library?

Regards

[bigrob3rto]

Answer after a slow debug proces and compare with the old version.
Version 2.x has a MTU exchange function which is called early during the connection phase.
Version 1.4 does not do any MTU exchange at connection start.

`/**

• @brief Begin the MTU exchange process with the server.

• @returns true if the request was sent successfully.
  */
  bool NimBLEClient::exchangeMTU() {
  int rc = ble_gattc_exchange_mtu(m_connHandle, NimBLEClient::exchangeMTUCb, this);
  if (rc != 0) {
  NIMBLE_LOGE(LOG_TAG, "MTU exchange error; rc=%d %s", rc, NimBLEUtils::returnCodeToString(rc));
  m_lastErr = rc;
  return false;
  }

  return true;
  } // exchangeMTU`

Connection can be called without the MTU exchange using optional argument:
`/**

• @brief Connect to an advertising device.
• @param [in] pDevice A pointer to the advertised device instance to connect to.
• @param [in] deleteAttributes If true this will delete any attribute objects this client may already\n
• have created when last connected.
• @param [in] asyncConnect If true, the connection will be made asynchronously and this function will return immediately.\n
• If false, this function will block until the connection is established or the connection attempt times out.
• @param [in] exchangeMTU If true, the client will attempt to exchange MTU with the server after connection.\n
• If false, the client will use the default MTU size and the application will need to call exchangeMTU() later.
• @return true on success.
  /
  bool NimBLEClient::connect(const NimBLEAdvertisedDevice pDevice, bool deleteAttributes, bool asyncConnect, bool exchangeMTU) {
  NimBLEAddress address(pDevice->getAddress());
  return connect(address, deleteAttributes, asyncConnect, exchangeMTU);
  } // connect`

SOLUTION: call connect method with false args:
pClient->connect(advDevice,false,false,false)

[h2zero]

Thanks @bigrob3rto, there seems to be a few devices around that are doing this now. According to the spec the connection initiator (client) is the only one that should be requesting the MTU exchange but these devices appear to be non-conforming so this is the best solution.