its upto your prgram ly...it will execute all the things at same speed ly.....each instruction will take some no.of machine cycles and it is upto the instruction and if you find the sum of those times from your program you can get it...
hi
there are many things are to be considered
first of all it depends on the compiler and it's optimization techniques.
how it convert the C code to Assembly and then Hex.the more the code, the more time it will take to exicute the code.
In ISR, there are many context saving techniques which used by the compiler which consumes machine cycle.
in assembly you can exatly predict the time consumed
which chip you are using.. we can tell you more one this.. 12.5us seems too short... your main will be interrupted a lot hope your ISR is not very long..