Proposal - drop the GPSD JSON driver

Hal Murray hmurray at
Sat Oct 22 18:17:07 UTC 2016

> What ntpd gets from a clock source is a series of pairs asserting "at system
> time X I believe it was UTC time Y".


> Are you telling me there is no value in minimizing the time from X to when
> the sample triggers a correction, and the variation in that time?

> Basic servocontrol theory tells me that control lag is the enemy of
> precision and tends to produce whiplash effects.  Does that not apply here? 

Not "no value", but it depends on the time constant of the PLL filter.  
Delays of a small fraction of the time constant won't be problem.

In the normal case, the data is put into a buffer and isn't processed until 
several/many seconds later.  So except for the last sample, any delay and/or 
jitter under a second doesn't matter.

Things will get more interesting if you try to run with minpoll of 0.

My current thinking is that we should either use a cleaned up SHM or the same 
struct over a socket.  The socket will fit in with the big select and has a 
reasonable chance of working well with minpoll of 0.

These are my opinions.  I hate spam.

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