[ntp:questions] Re: NTP for dummies

Ephraim F.Moya spam_mesg at microdrive.com
Sun Oct 2 00:39:44 UTC 2005

On Sat, 01 Oct 2005 23:09:47 +0100, david at djwhome.demon.co.uk (David
Woolley) wrote:

>In article <433E8CD6.7000904 at gis.net>, mayer at gis.net (Danny Mayer) wrote:
>> ntpd on Windows does set the CMOS clock, at least it's supposed to.
>Not in version 4.2.0 and I would consider it a bug for it to set
>in a later version as it would be redundant, would risk a conflict [A]
>with the kernel code that already does this, and might fail to
>implement the policy that only the low order part of the hardware
>clock is adjusted, to allow people to dual boot Windows, which
>requires the hardware clock to be in wall clock time.
>This code in the linux kernel (2.4.26) already ensures that the CMOS clock
>tracks a synchronised software clock (arch/i386/kernel/time.c):
>        /*
>         * If we have an externally synchronized Linux clock, then update
>         * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
>         * called as close as possible to 500 ms before the new second starts.
>         */
>        if ((time_status & STA_UNSYNC) == 0 &&
>            xtime.tv_sec > last_rtc_update + 660 &&
>            xtime.tv_usec >= 500000 - ((unsigned) tick) / 2 &&
>            xtime.tv_usec <= 500000 + ((unsigned) tick) / 2) {
>                if (set_rtc_mmss(xtime.tv_sec) == 0)
>                        last_rtc_update = xtime.tv_sec;
>                else
>                        last_rtc_update = xtime.tv_sec - 600; /* do it again in
>60 s */
>        }
>[A] not all versions of linux support /dev/rtc, which would be necessary, but
>possibly not sufficient, for user space code to update the clock atomically.

You seem to be describing linux only. ?? Is the same true for WinXP?
If not, what is true for WinXP?

ntp seemed a good solution since I thought I could forget about
calibrating it once I install it.

It seems that ntp may not be what I want. Can somebody recommend a
program for WinXP that will consult a time server once an hour (or so)
and set my hardware clock. I'd like it to be as independant as
possible since I envision it running in the background with no
attention from me.

FWIW the hardware clock on my computer drifts about 1.5 seconds per
day. I can set it by hand but I'm not fast enough to get within a
second and I don't want to mess with it normally.

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