Hmm, haven't tried varying the optimization level, a good point. But I have seen an assembly output of various C and C++ programs (not this one yet though) and there often was a few bytes of padding with NOPs before or after the final RET from the subroutine.

Copernicus, FREQUENCY and PERIOD are enums with values 0 and 1, respectively. You are right, there are only those two values so I could have used an if instead of a switch but I think the latter communicates the intention more clearly.

FWIW. the code has been completely refactored since last night and no longer exhibits the problem.