Huh, the discussion has drifted into some details, which are far beyond my skills 
But I like to thank you all for your contribution. I guess I gained understanding in what is atomic and what not ... thanks @bperrybap, but also @DrDiettrich, @Koepel and @J-M-L 
So I ask you understanding that I simply can not reply to all your responses .... at least not know, because:
Unfortunately, to actually check proper working of my buffer, I just turn out to be to stupid to set-up proper supporting function (well, not exactly, I'm trying to setup a new class (then to be used for buffer test, but also other porposes), but right now I failing in creating this class to work as intended 
)
So give me some time, I'll keep you posted.
Until then, for your entertainment, a picture of my HW-setup, which I used to test all the stuff. Not completed yet, but still quite good for HW-in-the-loop-tests.
