[time-nuts] Time source for indoor standalone PC

[mike cook]

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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