Situation: You want to include a timer interrupt service routine in an assembly language program for an AVR-based Arduino. The program will be written, assembled and uploaded using the Arduino IDE.

"So you are running your void loop() code, where you keep checking forever if some input or signal level or other reading is really necessary.\n", ...

but instead I found such an thorough and well thought-through answer on StackExchange that I thought I had to point it out. So, t0 the question: What is AVR Arduino interrupt latency? And how can it ...