in reply to
How to sleep 1 microsecond?
If you are on a modern operating system, you cannot do that reliably. An kind of sleep call is likely to trigger a task switch where the OS puts your process in the background executes another one. And even if you don't sleep, that can still happen.
If you absolutely need such exact timings (what for?) consider using a real-time operating system, and probably not Perl either (Perl does some stuff under the hood that can be harmful when you need exact timings. Examples are re-hashing of hash tables, and freeing variables on scope exit).