[time-nuts] NMEA time

Hal Murray hmurray at megapathdsl.net
Thu Nov 26 18:09:08 UTC 2009


ch at murgatroid.com said:
> These are both problems, but the biggest issue in reducing jitter
> often is minimizing SMM[1].  Some SMI's can suck up 50 us at a go
> though most are less.  On some platforms you may see SMI's executing
> at a rate of  more than 1 Hz. 

I think that's a different issue.  That adds jitter to measuring how long 
something takes.  It doesn't add jitter to what-time-is-it-now, at least if 
you are somewhat flexible on what you mean by "now".

How-long jitter can be filtered out or averaged, depending upon what you want.

It's a lot harder to keep accurate time if your basic clock changes 
frequency, say due to temperature.

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






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