Unless you have specifically arranged otherwise, the simulator assumes that your hardware design is perfect, that your software matches it perfectly, and your actual hardware is faultless and 100.00% to spec.

If any one or more of these assumptions is not 100.00% true - then you will, sooner or later, get a discrepancy between the target & simulator.

One way in which your software might not "match" your hardware is in terms of timing - especially at the margins.



Yes - it is very common indeed!