[ntp:questions] how do I lock in average frequency correction

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Wed Feb 15 06:19:29 UTC 2012

On 2/14/2012 2:54 AM, Chris Albertson wrote:
>> Perhaps a silly question, but, does the "tick" that drives the OS software
>> clock originate from the RTC or from the CPU master clock at 2 GHz or
>> whatever?  Just trying to understand how this stuff works.
> Look in the directory
> /sys/devices/system/clocksource/clocksource0
> On Linux there are two files.  One lists all the possible clock source
> the kernel found on your hardware.  There might be more then a few
> depending on what kind of computer you have.   Remember Linux runs on
> everything from cell phones to mainframes
> The other file tells you with clock source is actually being used.
> There is a way to force the selection at boot time.
> All that said, on a modern PC lilely you are using the hpet to cause
> periodic interrupts, each interrupt advances the system time by one
> tick.  hpet is the high precision timer.  Google will tell you all
> about hpet.
>    Ticks are between 100Hz and 1000Hz.  I think 1000Hz is common.  It
> is adjustable at boot time also
> I'd bet it is completely different on Windows systems an even other UNIXes
> Chris Albertson
> Redondo Beach, California
HI Chris,

Thanks for the info.  What a mess of different methods to create a clock 
tick.  I think I'll focus on trying to use the system rather than trying 
to understand it.  8-)




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Ron Frazier
timekeepingdude AT c3energy.com

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