USBSerial compilation error

Mbed OS
4

John,

above you wrote about MbedOS 5.15 and now you poste some links to mbed-dev, which is Mbed2.
And of course there are pins for the USB because the board DISCO-L053C8 | Mbed has USB 2.0 full speed on-chip interface. But unfortunately the USB driver for STM32L0 was not implemented under Mbed - STM32L0 HAL drivers.

You can try to do what I mentioned in this topic but because your board is low memory target you also need additional setting for activate USB under bare metal.

Probably something like this.

{
    "requires": ["bare-metal", "events","drivers-usb"],
    "target_overrides": {
        "*": {
            "target.device_has_add": ["USBDEVICE"]
        }
    }
}

But from me point of view after you will enable all necessary things then you will see this Error

– MbedOS Error Info –
This board does not have a hardware USB driver

EDIT:
Ok, the setting for bare metal above is for MbedOS6+ but not for MbedOS5. The USB API of MbedOS5 was probably not supported under bare metal.

BR, Jan