Nanosecond Timer on Arduino

Okay, I'm a complete noob to the forums.  I took a look to see if there were other topics like mine (there were) but I didn't see / may have missed the part where an idea like mine was proposed.  I found this topic:

https://www.robotshop.com/letsmakerobots/nanosecond-timing-too-fine-hobbyist

And posted this reply:

All right, I know this is an old thread, but does anybody know how fast it takes for a single instruction to be executed?

I'm using these compute times for reference.

It would take some knowledge of assembly, but couldn't you just make a simple loop for a single instruction that you knew the computation length of time of, told it to continue looping until some input linked to whatever action you were performing (laser beam hits a sensor, sensor sends the "interrupt" signal to processor) stops it, then used the number of completed loops times the length of time needed to perform that calculation to give us length of time?

You'd be off by about 3/4- to 1.606 of a nanosecond if the signal interrupted a loop somewhere in the middle, but it'd get pretty close, wouldn't it?  Just a thought. "

I was just wondering if it seemed feasible?

 

What about Raspberry Pi?

I’m guessing the idea is to divide 1 billion by whatever the processor speed is to get the nanoseconds / instruction figure?  If that’s the case, a single instruction on Raspberry Pi would be about 1.429 nS @ 700MHz?

I’m just trying to imagine a cheap solution that would “get 'er done”; that is (to me, anyway),a super high-speed timer that operates within pretty slim tolerances. A tolerance of plus or minus .715 nS would be sufficent for any imaginable application, outside of cutting edge physics experiments.

On the other hand…

This site has some operating within similar tolerances for like $5.