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

Dave Hart davehart at gmail.com
Wed Feb 15 06:39:09 UTC 2012

On Wed, Feb 15, 2012 at 06:04, Garrett Wollman <wollman at bimajority.org> wrote:
> In article <4F39FD1A.6020905 at c3energy.com>,
> Ron Frazier (NTP) <timekeepingntplist at c3energy.com> 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.
> Customarily, there's a really cheap crystal oscillator on the
> motherboard, and all of the other frequencies on the system -- except
> for the battery-backed RTC clock -- are generated by a clock-generator
> circuit which uses that frequency as a reference.
> Historically, the PC used frequencies which were convenient multiples
> of the NTSC colorburst frequency, because NTSC crystals were really
> cheap.

I believe it had more to do with the Color Graphics Adapter circuitry
needing to operate at NTSC-compatible frequency.l

Dave Hart

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