[time-nuts] Re: When did computer clocks get so bad?

[Thomas D. Erb]

Pre ubiquitous internet with NTP - we ran special projects with Windows PCs - 
but time keeping was always a problem - we would use one of our embedded 
controls with line frequency time keeping - which is very accurate - the funny 
thing when power went off we used the same Dallas Chip as on the PC for time 
keeping.  Also the embedded control has to be set to UTC 0 no daylight savings.

Thomas D. Erb
o:508-359-9684
p:508-359-4396 x 1700
f:508-359-4482
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e: t...@electrictime.com
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Tower & Street Clocks Since 1928

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[time-nuts] Re: When did computer clocks get so bad?

[James Perkins]

My Dad who taught Electrical Engineering told me that when parts are sold
in different quality grades (like resistors or in this case, crystals),
that the parts that meet the highest spec are sold for a high price, then
the next highest quality spec parts are sold for less, and so on. So your
typical 30ppm computer chip will probably have a bias that is either about
+25ppm or about -25ppm, but definitely NOT likely to be in the range -10ppm
to +10ppm.

Cheers,
James

On Wed, Sep 29, 2021 at 1:10 PM Alec Teal 
wrote:

> Hi there,
>
> I have a question and I cannot think of anyone better to ask, for a
> project we need to time some things which are connected to a computer,
> using NTP and later using a GPS over bluetooth serial ports, we have
> discovered that computer clocks are terrible
>
> If you remove a linear drift (for example assuming it ticks at 1.00026
> seconds per second) it gets less terrible, and Linux can do this but it
> is clear that the computer clock doesn't expose this coefficient to the
> OS to let it compensate, it must be found (eg through NTP) - any ideas why?
>
>
> But more concretely, my watch is actually pretty good, it's off by < 3
> seconds and hasn't been set probably this year (I don't tend to bother
> with DST stuff, not for any reason just never get round to it) - when I
> was growing up and even now wall-clocks are not so terrible that I have
> to fix them (or NTP does with computers) very routinely.
>
> My theory is that super cheap crappy quartz clocks are now used in
> things which can be reasonably expected to be online most of the time,
> and thus use NTP - my watch cannot (and probably has temperature
> correction too? Given the varied temps it is exposed to) any truth to this?
>
> This is a very open ended question I understand, but if clocks were as
> terrible as I've found every computer and thing I've checked recently,
> why don't I remember setting wall clocks easily once a week?
>
>
> Alec
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>

-- 
James Perkins   KN1X  www.loowit.net/~james
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Alternate email: 
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[time-nuts] Re: When did computer clocks get so bad?

[Trent Piepho]

On Wed, Sep 29, 2021 at 1:48 PM Poul-Henning Kamp  wrote:
> Since these embedded chips generally are incredibly robust with
> respect to timing, the xtal on the BOM is the cheapest that will
> meet spec.

Crystals?  We don't need no stinking crystals!

At least for the RTC.  Chips like, e.g. the NXP iMX6, can use an
internal ring oscillator in place of the customary 32kHz crystal to
save even more on BOM cost and board space.  Still needs a faster xtal
for full operation, but low power mode and RTC can use the ring
oscillator and keep the 24 MHz xtal powered down.
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[time-nuts] Re: When did computer clocks get so bad?

[Poul-Henning Kamp]

Alec Teal writes:

> So you suspect/expect around the time frequency changes started 
> happening, clocks became crap?

Well, it gets complicated fast there, but yes, that's pretty much
where the shit inescapably hit the fan.

Previous to that, most CPU's were clocked with a small PLL chip
which multiplied a 14.318MHz X-tal to whatever was needed.

"Not good, not terrible" is probably a fair summary.

But there are two different things at work here:  On one hand
the choice of Xtals:  To keep the jitter on the multiplied
clock low, the Xtal had to be better and better.  (This is
something the "extreme overclocking" people totally fail to
consider when doing their high-school physics experiments.)

But on the other hand, the CPU architecture must offer
/something/ to the kernel to keep time with, and that's what
Intel utterly fiasco'ed because of their windows focus.

The entire ACPI-solves-that, ACPI-without-gliches-solves-that,
reading-ACPI-is-faster-now saga was just sheer incompetence.

But the ACPI running at 14.318 MHz is inadequate for most modern
kernels in the first place, and that gets us into the TSC-counts-cycles,
TSC-counts-cycles-without-overflow-issues,
TSC-counts-cycles-onlyfor-this-core, TSC-pretends-the-core-is-
always-running-at-the-same-speed saga, which was also caused by
Intels idiocy.

Admittedly, there are good and sane explanations why this is
a hard problem to solve, but competent people solved in in
other architectures decades before Intel botched it.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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[time-nuts] Re: When did computer clocks get so bad?

[Bob kb8tq]

Hi

If your wrist watch is holding 3 seconds per year without some sort of external 
correction,  that’s pretty amazing …. 10 seconds a month is doing well.

Bob

> On Sep 29, 2021, at 2:35 PM, Alec Teal  wrote:
> 
> Hi there,
> 
> I have a question and I cannot think of anyone better to ask, for a project 
> we need to time some things which are connected to a computer, using NTP and 
> later using a GPS over bluetooth serial ports, we have discovered that 
> computer clocks are terrible
> 
> If you remove a linear drift (for example assuming it ticks at 1.00026 
> seconds per second) it gets less terrible, and Linux can do this but it is 
> clear that the computer clock doesn't expose this coefficient to the OS to 
> let it compensate, it must be found (eg through NTP) - any ideas why?
> 
> 
> But more concretely, my watch is actually pretty good, it's off by < 3 
> seconds and hasn't been set probably this year (I don't tend to bother with 
> DST stuff, not for any reason just never get round to it) - when I was 
> growing up and even now wall-clocks are not so terrible that I have to fix 
> them (or NTP does with computers) very routinely.
> 
> My theory is that super cheap crappy quartz clocks are now used in things 
> which can be reasonably expected to be online most of the time, and thus use 
> NTP - my watch cannot (and probably has temperature correction too? Given the 
> varied temps it is exposed to) any truth to this?
> 
> This is a very open ended question I understand, but if clocks were as 
> terrible as I've found every computer and thing I've checked recently, why 
> don't I remember setting wall clocks easily once a week?
> 
> 
> Alec
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[time-nuts] Re: When did computer clocks get so bad?

[ed breya]

I assume you're talking about the RTC chip that runs off the CMOS BIOS 
memory settings battery, to keep time whether the computer is on or off. 
These are as you suspect, typically cheap items that get the basic job 
done. You may be able to find better grade ones. It also depends on 
whether the timing crystal is built into the IC, or a separate piece. In 
this case, you could fairly easily hack in a reference that's as good as 
you want. Usually it's a 32.768 kHz "watch" type resonator, and 
disconnecting one end and hooking in an external source will drive it 
instead. If you provide the same nominal frequency, that's much more 
accurate and stable, can run the RTC under all conditions, and is always 
on, then it should keep time as good as your reference.


Ed
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[time-nuts] Re: When did computer clocks get so bad?

[Dana Whitlow]

Alec,

I seem to perceive that PC clocks have gotten quite a bit better since
their early days.  What do others think?

Dana

On Wed, Sep 29, 2021 at 3:10 PM Alec Teal 
wrote:

> Hi there,
>
> I have a question and I cannot think of anyone better to ask, for a
> project we need to time some things which are connected to a computer,
> using NTP and later using a GPS over bluetooth serial ports, we have
> discovered that computer clocks are terrible
>
> If you remove a linear drift (for example assuming it ticks at 1.00026
> seconds per second) it gets less terrible, and Linux can do this but it
> is clear that the computer clock doesn't expose this coefficient to the
> OS to let it compensate, it must be found (eg through NTP) - any ideas why?
>
>
> But more concretely, my watch is actually pretty good, it's off by < 3
> seconds and hasn't been set probably this year (I don't tend to bother
> with DST stuff, not for any reason just never get round to it) - when I
> was growing up and even now wall-clocks are not so terrible that I have
> to fix them (or NTP does with computers) very routinely.
>
> My theory is that super cheap crappy quartz clocks are now used in
> things which can be reasonably expected to be online most of the time,
> and thus use NTP - my watch cannot (and probably has temperature
> correction too? Given the varied temps it is exposed to) any truth to this?
>
> This is a very open ended question I understand, but if clocks were as
> terrible as I've found every computer and thing I've checked recently,
> why don't I remember setting wall clocks easily once a week?
>
>
> Alec
> ___
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>
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[time-nuts] Re: When did computer clocks get so bad?

[Poul-Henning Kamp]

Alec Teal writes:

> My theory is that super cheap crappy quartz clocks are now used in 
> things which can be reasonably expected to be online most of the time, 

There are multiple answers to your question.

The funny one is:  When they set fire to a prototype motherboard
at Intel Architecture Labs.

Unfortunately that is not my story to tell.

But for the PC-ecosystem, that really is the answer:

When Intel had to start modulating clock-frequency in order to not
set things on fire.

Their execution was far from stellar, because they had their eyes
only on Windows, which for all intents and purposes had no timekeeping
worth anything at the time.

By now they have it relatively under control, and due to the very
steep PLL multipliers high end kit actually have comparatively
good XTALS in order to keep the jitter within spec.

For the Internet of Shit segment, the answer is it was never any
good to begin with.

Since these embedded chips generally are incredibly robust with
respect to timing, the xtal on the BOM is the cheapest that will
meet spec.

The one saving grace is external high-speed interfaces like USB-3
and 10G ethernet:  You need good-ish xtals before it even works.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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