Thanks to Bill3D for a useful hint. I have added the information to my Feedback Assistant report. I will try your suggestions presently and will report here what happens.

MobileTen's link is very useful, but I could also use some information on how to access arguments to a C++ function call from assembler within the function. I think there is a special syntax for dealing with inputs and outputs between C++ and embedded assembler, but I do not know how to use it for CLang. Any pointers, anyone?