How can one use an USB OTG serial interface on Android, in Qt?

Question

I intend to port a Qt desktop application to Android. It uses QSerialPort to communicate with an external device (which has a built-in CP210x)

The application, although written purely in Qt and C++, runs fine on Android, but it doesn't see the device. The CP210x official driver download page recommends to compile the kernel on Android from source, which is not feasible to expect from the average customer. Other recommendations I found online recommend jailbraking the phone, which also isn't something we could expect end users to do.

There are scant few questions in this topic on the Qt forums, most saying that QSerialPort's Android support is quite limited. However, these topics are often at least 6-7 years old.

An Android developer forum/wiki/tutorial? recommends to use "Android Things", whatever it is. I couldn't find any apps fitting that description.

I know that it's physically possible to use serial-usb on an non-jailbroken Android, as I tried out a serial console app and it worked, I could successfully exchange data with my device.

Does this mean that the only was is to develop my own wrapper in Java, and use JNIEXPORT? That would break the easy multi-platform compilation I used before (just selecting a different kit from Qt Creator) Are there any simpler ways to accomplish this? Is USB OTG usage so low that no one else thought to implement anything in this regard?

Answer 1

QSerialPort has only a non-official partial Android Support (see https://wiki.qt.io/Qt_Serial_Port ).

(... Use on own risk, only for rooted devices, in which is it possible to get/set a permissions to the /dev/ttyXYZ nodes)

You can use JNI to get a FileDescriptor with permission and then use the libusb library in C++ to communicate with device. But yes, it would break the easy multi-platform compilation.