if (isMarlinPrinting) possible?

Hello !

I am the overall newbie to Marlin and 3D printing and currently facing a high-school project with the aim to construct and integrate a 3D Marlin Printer with a workpiece feeding controlled by an arduino uno. Therefore we need to communicate the printers and the feeding-systems state like "printing", "feeding", "workpiece finished" and so on. The simpliest way would be to integrate another G-Code into Marlin saying "printing starts" or "printing finished" and put these codes in any G-Code file sent to the printer. But I think that's not what engineers do - we want modular systems! I had 3 months for Marlin, RAMPS, RepetierHost, security issues, steppers and torsion-enforcing oldham-style-type clutches, but teaching my self C++ and reverse engineering Marlin within 6 weeks didn't work in the end :-)

HERE IS THE QUESTION: So perhaps there is someone here in the community who is IN the code and knows a simple possibility to check within marlin periodically, if it is actually printing. As I understood the code so far, data sent by RepetierHost is buffered and the buffer runs out from time to time, so RepetierHost can send the next commands - thus I can't use it for my purpose (I think so ?!?).

Thanks for every help in advance!