I have to calculate the time of an interrupt when it begins untill its end.I try to set a bit on the microcontroller when the interrupt begins and clear it when interrupt ends. Tnen i will take that bulse with another bulses from an external clock to be an AND GATE input .the output bulse from the AND GATE will be entered to a counter.It is my idea to do what i want but i think it is too long :( .Is there any other idea more easier than it?

Thanks