[time-nuts] Time source for indoor standalone PC

[Eric Williams]

Right, that's why I brought up the GPS sentences.  You'd need a small micro
to read the chronodot registers and output formatted serial, the 1pps can
go directly to the PC.


On Fri, May 17, 2013 at 3:24 PM, mike cook <mc235960 at gmail.com> wrote:

>
>
>
> Le 17 mai 2013 à 22:52, Eric Williams a écrit :
>
> > That's based on my experience, but I did go in and tweaked the offset
> > register in mine over the course of a month or so.  I think it has gotten
> > off 3-4 seconds in a year.
> >
>
>  I have found the same, BUT, they are not a solution to the issue. The
> reason is that the OS doesn't read the RTC after initial boot sequence,
> when the system clock is initialised. All clock references are to the
> system clock from there on until orderly shutdown when it is updated from
> the system clock value.
> So it will give an accurate time at boot, but the system clock stability
> will predominate from there. My Raspberry Pi which has one of these
> installed has a 40ppm clock drift even though the RTC does better. I need
> NTP to get correct it.
>
> >
> > On Fri, May 17, 2013 at 1:33 PM, Tom Van Baak <tvb at leapsecond.com>
> wrote:
> >
> >>> Even something as simple as a Chronodot will hold to a few seconds a
> >> year.
> >>
> >> Eric,
> >>
> >> Are you sure? My understanding is that the Chronodot is based on the
> >> DS3231. Quoting http://datasheets.maxim-ic.com/en/ds/DS3231.pdf we
> read:
> >>
> >>    The DS3231 is a serial RTC driven by a temperature compensated 32kHz
> >> crystal oscillator. The TCXO provides a stable and accurate reference
> >> clock, and maintains the RTC to within ±2 minutes per year accuracy from
> >> -40°C to +85°C.
> >>
> >> /tvb
> >>
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