CMOS, daylight saving time and dual-boot

[Mike Lempriere]

If you're in the US, you're a week early for the changeover -- your 
timezone files need to be corrected.
See: http://articles.techrepublic.com.com/5100-10877_11-6163042.html

Eugene Grosbein wrote:
> On Mon, Oct 29, 2007 at 02:17:44AM +1100, Ian Smith wrote:
>
>   
>>  > I have dual-boot machine with 7.0-BETA1 and Windows
>>  > that keeps CMOS time local (there is /etc/wall_cmos_clock also).
>>  >
>>  > It was tuned off yesterday evening and turned back on today,
>>  > loading FreeBSD. Meantime the switch from Summer Time to Standard Time
>>  > has ocurred. There is 'ntpd_enable="YES"' in /etc/rc.conf.
>>  > Nothing in a system reacted on the end of Summer Time period,
>>  > so ntpd just complained about 3600 seconds exceeded sanity limit
>>  > and bailed out (documented behavour).
>>
>> With standard /etc/crontab, adjkerntz -a (which catches DST changes) is
>> only run between midnight and 5am, and presumably your 'today' started
>> after then.
>>     
>
> Yes, really much later :-)
>
>   
>> Perhaps running that once on boot, just in case, might help
>> in such circumstances?
>>     
>
> I'll test this. By the way, I cannot set local date
> to '02:59:00 summer time', it sets '02:59:00 winter time' :-(
> E.g., "date 200710280222.39" sets time in "KRAST" timezone
> (local time is GMT+8 in summer) and "date 200710280222.40"
> sets it so timezone changes to "KRAT". How could I set it
> to "200710280259 KRAST"?
>
>   
>>  I've done that without ntpd running, but ntpd
>> -qg once on booting should handle such surprise 3600s shifts better?
>>
>>  > There is Status Register B at the offset 0x0b in the ISA Compatible
>>  > CMOS its least significant bit should keep Daylight Saving flag
>>  > (on/off). 
>>
>> The bit appears to be DST enable, rather than storage of current state?
>> Windows date setting has a check box that I suspect reflects this bit. 
>>     
>
> I don't think so, it seems that Windows keeps it's own flag
> to know if it should adjust local time for daylight savings.
> As you noted, FreeBSD always clears CMOS bit and
> that has no affect on Windows behavour.
>
>   
>> You may find that windows will shift CMOS another hour when next booted
>> too, or at least that's what I recall W98 doing to me a couple of times
>> when I happened to boot it some time during some 6 month period :)
>>
>>  > Is it used in modern hardware? Does FreeBSD use it? It is supposed to
>>  > use it? 
>>
>> /sys/isa/rtc.h has
>> #define  RTCSB_DST       0x01   /* USA Daylight Savings Time enable */
>>
>> but it's not referenced in /sys/i386/isa/clock.c (great bedtime reading) 
>> which is the only place that updates the RTC, AFAIK.  If I'm reading it
>> right, FreeBSD clears this bit during clock initialisation. 
>>
>> (5.5-STABLE here; I haven't checked if this code has changed since) 
>>     
>
> The same in CURRENT. It seems we could use this bit as storage flag :-)
> I think about diskless stations that has no other storage for this.
>
> Eugene
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>
>
>   

-- 
Mike Lempriere- Home: mike at vintners.net  Phone: 206-780-2146
Cellphone: 206-200-5902;  text pager: mlemp at tmail.com