Tweaking the wallclock, non-NTP

Wallclock in my PC gains a second or two each week. Normal, I guess, but irritating. I don't want to use NTP, as an exercise, and I'm just wierd like that. Couple of years ago, I looked for a sysctl knob or loader setting, but could not find one that would help. Maybe I did not look hard enough. Maybe things have changed.

Anyway, ntp_adjtime(2) does seem to work set-and-forget kind of way too. Simple utility attached. Using trimclk -f -3.35 the clock now loses a millisecond per day, more if heated up.



  • trimclk.c.txt
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Thanx for the code snip. I'm just thinking, I should do something similar to substitute my GPS clock to use in place of internet servers. Should be easy.
An oven glued to the crystal would be nice. This is too cramped and miniature to do that.

As it happens, this laptop has a builtin GPS. I check the difference hourly, and adjust with adjtime(2) (in addition to that boottime ntp_adjtime) as needed. clock icon click. Although the GPS is behind an USB tty, and is not serious hw by a mile (no PPS or anything) the start of the NMEA blurt each second is accurate to 1 msec and better. Usually. If not loaded :)

The accuracy is nice (with or without PPS). More important for my purpose is the ability to be free of any internet connections.