Re: PSA: Clock drift and pkgin

[Paul Koning <paulkoning%comcast.net@localhost>]

> On Dec 13, 2023, at 4:04 PM, Johnny Billquist <bqt%softjar.se@localhost> wrote:
> 
>> ...
> 
> If we don't have lost clock interrupts, the only source of drift (assuming we don't have ntp or something else setting the system up for slow time adjustment), would be the chrystal itself. I know that the chrystal used in VAXen aren't perfect, and you do have some drift from that. But that is completely independent of load.
> But a drift of a couple of % would not be unexpected.

Um, yes, it would be unexpected.

The crystal spec in that era was 0.01%, which was the typical spec for ordinary commercial grade crystals.  Nowadays better specs are not unusual, and watch crystals (32768 Hz) have always been made to tighter specs, but the tolerances for MHz-range crystals were traditionally governed by what could be delivered cheaply and what was good enough for radio applications.

If you see a couple % drift, that's definitely not the crystal.  And, unlike PDP-11s, VAXen don't use a power line frequency reference for the system timekeeping.

	paul