Hello Everyone,
I am in the midst of a design for a
new custom CPU board. I decided
to include NTP, in the board software,
for time keeping purposes.
The system is working rather well and
I am able to get millisecond time sync.
BTW this is as good as I'll get
on this hardware.
The background is this:
I am using a PID Control loop to discipline
the time and I am wondering if my algorithm
is the correct one.
This is what I do:
Get NTP time every T seconds
Calculate error
Calculate correction
Apply correction slowly.
This means that if the correction is: C
and if my smallest system clock increment is: I
and if there are N clock increments until
the next NTP get time.
Then I apply a correction of: C/N for every I.
In other words, the correction is smooth
over the NTP sync interval (T).
This method works quite well and the system
reaches <100ms sync at almost (10T).
It reaches <10ms at almost (20T)
And this is my question:
Should I be correcting the system this way
or should I be correcting all at once at the
time of NTP sync.
Should I expect a better convergence
if I use the all at once method?
Your thoughts on this are much
appreciated.
George Hrysanthopoulos, N2FGX
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