使用 Qt 的“QlowEnergyController”的两个实例连接到两个 BLE 设备

Question

Problem

I want to use Qt's Bluetooth Low Energy to connect to two BLE devices.

System

• OS: Arch Linux 4.13.8
• bluez version: 5.47
• BLE adaptor: Cambridge Silicon Radio, Ltd Bluetooth Dongle (HCI mode)

Solution

I use have two QLowEnergyControllers instances like this:

controller0 = QLowEnergyController::createCentral(qBluetoothDeviceInfoBLE0, this));
controller1 = QLowEnergyController::createCentral(qBluetoothDeviceInfoBLE1, this));

If then successfully conneect with BLE0 , and after the signal connected() is emited, I initiate a connection to BLE1 . The connection to BLE0 will be aborted:

qt.bluetooth.bluez: Cannot connect due to pending active LE connections
qt.bluetooth.bluez: void QBluetoothSocketPrivate::_q_readNotify() 17 error: -1 "Software caused connection abort"

... and the connection to BLE1 will be established successfully.

Found

What I found is this description in QLowEnergyControllers :

It is important to mention that some platforms such as a BlueZ based Linux cannot maintain two connected instances of QLowEnergyController to the same remote device

Note: BLE0 and BLE1 are different remote devices.

I can also confirm that connecting to the same devices works with my version of bluez. It also works when using nodejs' package noble.

Questions

1. Should it work as I have done it above? (connect to BLE0 , and afterwards BLE1 )?
2. I was thinking of using a second adaptor, is it correct that QBluetooth can only use one adaptor (the default one)?
3. Can somebody think of any workaround?

Answer 1

This is fixed by now (QT 5.11, BlueZ 5.50, Raspian, tested with RPi 4). I can easily create two instances of QLowEnergyController .

However, there can only be one QBluetoothDeviceDiscoveryAgent active at a time. That means one has to discover all devices first and afterwards connect to them by creating a separate QLowEnergyController object for each peripheral.

Here is a great short example https://bugreports.qt.io/browse/QTBUG-73809