Re: [ARMini-support] Is it possible to get the correct time
- From: Jim Lesurf <jcgl@xxxxxxxxxxxxxxx>
- To: armini-support@xxxxxxxxxxxxx
- Date: Sun, 29 Mar 2015 09:59:29 +0100
In article <57d8d8ab54.Andrew-Pin@xxxxxxxxxxxx>, Andrew Pinder
<Andrew.Pinder@xxxxxxxxxxxxx> wrote:
>
> Give the reported problems about smaller errors not being corrected,
> I'm wondering what people have experienced with the switch to BST.
FWIW the clock on my ARMiniX had drifted about 10 sec since I set it a few
days ago. I set it OK with the program I wrote and it wasn't concerned
about BST. (It deals with the underlaying UTC and the RO setup applies the
zone correction.) Seemed consistent with my machine's clock being off
by one or two seconds a day. (i.e. 10 - 20 ppm.)
> After syncing at boot, my clock is currently 0.616643 seconds slow,
> timer latch 129911 (+684ppm).
Erm, I doubt people will be getting results via net adjustments of the type
the OS does where you can state 'accuracy' to the nearest microsecond! To
do that you'd probably have to put in some work calibrating the time delays
in sending and getting times over the net. I suspect people would be better
keeping values to about a centisecond. That's if you have reasons to be
concerned at that level.
And as I've suggested before, if people want to do this they'd also need to
give detailed histories of when the machine was on/off, when any time
nudges were made, etc. Otherwise it will be almost impossible to compare
results and make any sense of how they may vary.
If you want serious accuracy you'd be better looking for a radio time
standard I suspect.
Also...
If my quick calculation is correct the rate offset you quote would
nominally remove the error in about 15 mins. If you have the OS time
system set to re-correct at a set interval, note that if that time is
too long the error will 'saw' back and forth between fast and slow.
Again, to know more you'd need to measure again just before you shut
down the machine (having noted how long it was on and when any auto
corrections were done). Then note how long it was off when repeating the
process when you start it up again. If you don't do this the values
you get may just seem random.
Jim
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