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SubjectRe: updating the RTC automagically
On 22 Nov 99, at 15:11, Guest section DW wrote:

> On Mon, Nov 22, 1999 at 08:18:31AM +0200, Ulrich Windl wrote:
>
> > Wel, well. How do you explain that the system clock is still the same
> > after having used "date -s" several times?
>
> Ulrich,
> If you have a buggy date(1) program, get a better one or complain
> to its maintainer.
> If you have a buggy kernel, complain on this list that the kernel
> is broken, preferably with details about what goes wrong.
> But the present discussion was not about fixing something,
> but about adding new functionality, and I and others thought
> that that might be a bad idea.

run RTC is localtime; date -s; reboot; wrong time if time corrected more than a few minutes.
I think it's an issue. (Imagine power failure instead of ordinary
reboot)

>
> By the way, on many alpha's the settimeofday system call is broken.

Wouldn't be much surprised, but can't comment.

>
> > Should each system have a cron job to update the RTC via hwclock
> > hourly, or maybe update it during system shutdown?
>
> The scheme where every 11 min RTC is overwritten by system time
> has disadvantages if one wants high precision.
> One can observe the drift of the RTC with very high precision
> by leaving it alone for a long time.

Already implemented. (See earlier message)

>
> The ideal setup would never write the RTC, but only read it,
> and keep notes on the deviation and the drift, so that some
> user space program can set system time from RTC plus this
> information in case no better outside time source is available.

That's a big matter of taste IMHO.

>
> The scheme where RTC is set every 11 min is much worse -
> each time an error of up to 0.5 sec is introduced, and
> such schemes make it impossible to get very reliable data
> on the drift of the RTC.

Why do you think I fixed it? Maybe just for you ;-)


>
> Many programs that try to adjust for drift are now confronted
> with a sawtooth effect that is much more complicated to handle
> than a linear drift. And while the linear drift is to a first

The sawtooth you are referring has many different reasons.

> approximation constant, independent of the OS running, this
> sawtooth is present only when the machine is up, running Linux,
> and with STA_UNSYNC unset.

[...]

U.


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