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Daylight saving come up soon

 
 
Arne Vajh°j
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      03-09-2008
Roedy Green wrote:
> On Fri, 07 Mar 2008 19:08:18 -0500, Arne Vajh°j <(E-Mail Removed)>
> wrote, quoted or indirectly quoted someone who said :
>> I can not see any point in this utility.
>>
>> Windows changes DST automatically and has done so for
>> many years.

>
> But it doesn't work reliably.


It has always worked reliable for me.

And if you read some of the other comments, then it is
apparently also working reliable for others.

Arne
 
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Roedy Green
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      03-09-2008
On Sat, 08 Mar 2008 21:20:16 -0500, Arne Vajh°j <(E-Mail Removed)>
wrote, quoted or indirectly quoted someone who said :

>He probably just meant USA and Canada.

For details of what I meant, see http://mindprod.com/jgloss/dst.html
--

Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com
 
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Roedy Green
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      03-09-2008
On Fri, 07 Mar 2008 09:59:22 GMT, Roedy Green
<(E-Mail Removed)> wrote, quoted or indirectly quoted
someone who said :

>For North Americans daylight saving starts Sunday March 9.


My radio-synched desk clock ticked over as advertised.
see http://mindprod.com/bgloss/radiosynchedclock.html

However Vista ticked over 2 hours. I will have a peek in BIOS. Perhaps
it did a kick over too.
--

Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com
 
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Roedy Green
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      03-09-2008
On Sun, 09 Mar 2008 01:09:59 GMT, "Karl" <(E-Mail Removed)>
wrote, quoted or indirectly quoted someone who said :

>I have never had problems with any Windows NT-based system including, NTP,
>DST, time zones, etc.


By that do you mean you cross checked with a radio synched clock, a
web atomic clock etc. or just that it behaved within a minute or two
to the time on the TV?

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Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com
 
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Martin Gregorie
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      03-09-2008
Karl wrote:
> I have never had problems with any Windows NT-based system including, NTP,
> DST, time zones, etc.
>

How easy would it be to port the Jonathon Buzzard's shared memory
interface? The *NIX version relies on the shared memory functions in the
SVR4 Inter Process Communication package. C, not Java of course!

>
> There are minor difficulties if the hardware timebase is not accurate,
> causing wind speed anomalies when it syncs with network time, but that isn't
> Windows' fault.
>

Has XP done away with the older Windows trick of copying the HW clock
registers into memory, updating them on the 18 ticks/second timed
interrupt and ignoring the HW clock until next reboot?

That was responsible for quite a lot of clock drift since, when Windows
got busy it tended to miss the timer ticks.


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martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
 
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Martin Gregorie
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      03-09-2008
Roedy Green wrote:
> On Sat, 08 Mar 2008 21:20:16 -0500, Arne Vajh°j <(E-Mail Removed)>
> wrote, quoted or indirectly quoted someone who said :
>
>> He probably just meant USA and Canada.

> For details of what I meant, see http://mindprod.com/jgloss/dst.html
>

GPS is useful as a time source as well as setting your location, which
only happens once per OS install. It can provide a time standard that's
been cleared of propagation delays because the GPS receiver must have
such a cleaned time in order to work at all.

This is unlike all other common time sources such as radio broadcast
time (WWV, MSF, etc) and internet time sources, which must all be
corrected for propagation delays before they can be considered accurate.
Unless, of course, its a broadcast time source and you're fairly close
to the transmitter.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
 
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Dr J R Stockton
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      03-09-2008
In comp.lang.java.programmer message <47d3495c$0$90274$(E-Mail Removed)
site.dk>, Sat, 8 Mar 2008 21:20:16, Arne Vajh°j <(E-Mail Removed)>
posted:
>Dr J R Stockton wrote:
>> In comp.lang.java.programmer message <rb22t3hh8skch17as5jn922ae19a79e159
>> @4ax.com>, Fri, 7 Mar 2008 09:59:22, Roedy Green <(E-Mail Removed)
>> om.invalid> posted:
>>> For North Americans daylight saving starts Sunday March 9.

>> Some North Americans do not have Summer Time.
>> NRC thinks that Newfoundland changes at 00:01 clock time (which IMHO
>> gives a risk of advancing the date, in Autumn, twice).
>> I believe that Mexico is in North America, and uses different
>>dates.
>> I believe that Greenland is in North America, and uses different dates.

>
>He probably just meant USA and Canada.


(a) I go by what he wrote, not what he might have meant.
(b) Newfoundland is a part of Canada.

--
(c) John Stockton, nr London UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME.
Web <URL:http://www.merlyn.demon.co.uk/> - FAQish topics, acronyms, & links.
For news:borland.*, use their server newsgroups.borland.com ; but first read
Guidelines <URL:http://www.borland.com/newsgroups/guide.html> ff. with care.
 
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Roedy Green
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      03-09-2008
On Sun, 09 Mar 2008 19:43:58 +0000, Martin Gregorie
<(E-Mail Removed)> wrote, quoted or indirectly quoted
someone who said :

>Has XP done away with the older Windows trick of copying the HW clock
>registers into memory, updating them on the 18 ticks/second timed
>interrupt and ignoring the HW clock until next reboot?


java.lang.System.currentTimeMillis nominal resolution is measured in
ms. It seems to me I have seen resolution higher than 18 ticks a
second, so at least that must to looking at a higher resolution timer.

It seems to me I noticed something around the time of NT that lead me
to believe system time was being handled more accurately, but that was
a long time ago and I can't recall details.

I recall though dealing with ticks and lost ticks in DOS.

You could do an experiment to see if
java.lang.System.currentTimeMillis returns numbers in some non-1-ms
multiple.

System.nanotime is using the instruction counter clock.

--

Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com
 
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Karl
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      03-09-2008


"Roedy Green" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Sun, 09 Mar 2008 01:09:59 GMT, "Karl" <(E-Mail Removed)>
> wrote, quoted or indirectly quoted someone who said :
>
>>I have never had problems with any Windows NT-based system including, NTP,
>>DST, time zones, etc.

>
> By that do you mean you cross checked with a radio synched clock, a
> web atomic clock etc. or just that it behaved within a minute or two
> to the time on the TV?


Most of the computers I have used to test my software remain accurate to the
second in comparison with a radio sync clock. They synchronize weekly with
NTP.

Windows uses the system timer hardware interrupt as a time base for time of
day functions. Since the system timer is a shared resource (on any system),
there are some cases where conflicts can arise. Operating systems have to be
aware if an application reprograms the timer, and notify all interrupt
handlers so that they can all can change their calculation constants. If the
clock is run at too high a resolution, interrupts can be missed, and time of
day accuracy suffers. Furthermore, the setting might be incompatible with
some handlers (usually too slow). If the timer is reprogrammed frequently,
some counts can fall through the cracks while the interrupt handlers
scramble to adapt. Some of these issues might be considered bugs, but some
are unavoidable. This bug
(http://bugs.sun.com/bugdatabase/view...bug_id=4500388) is probably due
to Java reprogramming the system timer.

In addition to programming issues, the accuracy of the hardware crystal time
base affects how much the computer time will drift. Any drift will cause a
discontinuity when it syncs with NTP. If the discontinuity is large enough,
in my application it can adversely affect time-critical wind speed
measurements. In that case, the work-around is to sync more frequently, so
the discontinuity is less. Or, do not sync automatically, and manually sync
the clock during system maintenance.

Here is an article that describes some timing considerations in Windows.
http://msdn2.microsoft.com/en-us/magazine/cc163996.aspx. Note that similar
considerations apply for other operating systems. In our case, we hope the
Java VM implementation can virtualize differences between platforms.


 
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Arne Vajh°j
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      03-09-2008
Roedy Green wrote:
> On Sun, 09 Mar 2008 01:09:59 GMT, "Karl" <(E-Mail Removed)>
> wrote, quoted or indirectly quoted someone who said :
>> I have never had problems with any Windows NT-based system including, NTP,
>> DST, time zones, etc.

>
> By that do you mean you cross checked with a radio synched clock, a
> web atomic clock etc. or just that it behaved within a minute or two
> to the time on the TV?


Actually I am not sitting at that time and looking at the monitors ...



But it works fine the day after.

And if you consider how time is implemented in modern
computers then there is really no way it can go wrong.

Because time is not changed at all. The offset that is
applied when formatting the time for output or parsing the
time in input is changed.

And the offset must be dynamicly calculated based on the
not changed UTC time.

Arne
 
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