[ntp:questions] Setting up a NTP Time Server

Unruh unruh-spam at physics.ubc.ca
Thu Apr 10 05:56:11 UTC 2008

hal-usenet at ip-64-139-1-69.sjc.megapath.net (Hal Murray) writes:

>>>You also get jitter from the OS (and serial port hardware).
>>>There should be a simple recipe to minimize that.  I haven't
>>>seen one and several tries haven't produced anything that
>>>I'd call good-enough.  (When I run out of other things to
>>>work on...)

>>What is good enough?

>Something I can easily measure.

Well, apparently you can measure it-- "You also get jitter from the OS..."
suggests that you measured something. But that is not good enough. 

The serial port I seem to recall has a worse behaviour of the interrupt
than does the parallel port. 
But what you can do is a loopback-- put some output onto one of the output
pins of the serial port which loops back into the interrupt port. timestamp
the raising of the pin on the output and timestamp the interrupt and see by
how much they differ. That of course measures only the total out-in time
but it is an indication of how the serial interrupt works. do the same for
the parallel port. 

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