[time-nuts] Discipline an oscillator with NTP?

michael taylor mctylr at gmail.com
Fri Jul 22 21:08:04 UTC 2011


On Fri, Jul 22, 2011 at 2:48 PM, Javier Herrero <jherrero at hvsistemas.es> wrote:
> El 22/07/2011 20:39, michael taylor escribió:
>>
>>
>> I think all NTP server appliances have this functionality by their
>> nature, whether or not the oscillator is of particular high quality
>> (low noise) or not. Many of the low-end ones likely just use a
>> standard oscillator "in a can" [2] that the embedded processor uses.
>
> No, ntp algorithm does not adjust the oscillator itself.

Yes, while the NTP algorithm or protocol does not adjust the
oscillator (or RTC) hardware directly, it does pass trimming or
de-skewing recommendations via software (ntp_adjtime, adjustime, or
hardpps) to OS, allowing the OS to adjust its system's clock.

But in the case of a NTP appliance (or embedded device), having
intimate knowledge of a single design means that the appliance's
Operating System could implement ntp_adjustime or hardpps to a VCO
(voltage controlled oscillator) via a DAC, a DDS or similar, to
actually fine time the device's master oscillator. Which becomes
worthwhile if there is an high quality oscillator driving (or
steering) the computer hardware's system clock, such as an OCXO or
Rubidium oscillator.



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