[time-nuts] [Solved] Looking for multiple PPS timestamp logging

[Hal Murray]

> I was thinking about the parallel port polling idea, but then my son wanted
> to measure the relation between temperature and XO frequency, so we needed
> microsecond resolution.

Why do you need microsecond resolution?

A junk XO will drift ballpark of 1 PPM per C.  That's 86 ms per day or 3.6 ms 
per hour.


What sort of resolution do you think you can get from a parallel port?

It might be fun to see how far you can push the parallel port.

How about a loop like this:
Initialization:
  grab old time
  grab old parallel port data
loop:
  grab new time
  grab new parallel port data
  if data changed:
    grab newer time
    log change that happened somewhere between old time and newer time
  old time = new time
  old data = new data
  goto loop

Post processing can filter out the occasional samples with a wide time window 
because the scheduler ran some other job at the wrong time.

For extra credit...  Suppose  you are expecting PPS type signals and you know 
roughly where they are located within a second.  There is no point is 
spinning when you aren't expecting something to happen.  So you can sleep 
until a bit before the next event.   That will let the scheduler run other 
jobs.  Hopefully it will be nicer to you when you do want to run.


-- 
These are my opinions, not necessarily my employer's.  I hate spam.