Truthfully, it might be C. It’s wrapped up into a C++ application now. You are absolutely correct about the timing problems with this code. You can’t even insert a debug statement into it without causing failure. It’s written deterministically, single threaded, synchronous operation and with specific timings. It is almost antithetical to modern operating systems.
I’m not responsible for the user mode application beyond getting all these timing messes to work flawlessly somehow. This has been a fun adventure in debugging the thing that doesn’t want to be debugged.