> Hence, wouldn't Best Practice be boxes loaded with only the bare OS and 
> software for the time-related tasks?

If you find yourself in a situation like this -- where your timing seems to 
improve the less load you have -- that's a sure sign that you're doing the 
timing wrong in the first place.

Best practices are to do 1PPS timing in hardware using capture registers (which 
almost every microcontroller has). That way there's a separation between the 
critical act of *making* a timing measurement from the non-critical act of 
*delivering* the measurement result the operating system. You still use 
interrupts -- but now the purpose of the interrupt is simply to indicate that a 
fresh measurement result is ready, rather than the interrupt itself being the 
measurement. The result is that the time stamp / capture register method is 
immune to interrupt latency and system load issues.

Best practices number two are to replace the crystal on the motherboard with a 
TCXO or OCXO. Then, with the help of NTP, your computer is finally acting like 
a GPSDO.

/tvb

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