PC clock generator without 14.318MHz
Hello,
I have operated own NTP servers with stable system clock for many years.
The principle is quite simple - I replaced 14.318 MHz quartz with OCXO
based circuit. Now I have to build few more servers with modern mini-ITX
motherboards, however on many of them (e.g. from ASUS) I can’t find any
14.317 MHz quartz. Such frequency is a relic of original PC design and
I wonder if it is used any other basic frequency in recent clock generators?
thanks,
Vladimir
On Tue, 18 Oct 2016 16:53:15 +0200, you wrote:
14.317 MHz quartz. Such frequency is a relic of original PC design
It's 4X the color subcarrier frequency in NTSC (originally U.S.)
television; rapidly becoming a dinosaur. I'm sure it was used in computers
to make color video easier. Newer boards doubtless use much faster clocks
and synthesize what the parts need.
]'
--
Gary Woods AKA K2AHC- PGP key on request, or at home.earthlink.net/~garygarlic
Zone 5/4 in upstate New York, 1420' elevation. NY WO G
In message ep0d0ctbrovmisvj43j57ns6smt606t3fs@4ax.com, Gary Woods writes:
On Tue, 18 Oct 2016 16:53:15 +0200, you wrote:
14.317 MHz quartz. Such frequency is a relic of original PC design
It's 4X the color subcarrier frequency in NTSC (originally U.S.)
television; rapidly becoming a dinosaur. I'm sure it was used in computers
to make color video easier. Newer boards doubtless use much faster clocks
and synthesize what the parts need.
It's 14.3181818 MHz and it has a most facinating history - if you care
for that sort of thing:
https://en.wikipedia.org/wiki/Colorburst#Rationale_for_NTSC_Color_burst_frequency
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.
Le 18 oct. 2016 à 16:53, Vladimir Smotlacha vs@cesnet.cz a écrit :
Hello,
I have operated own NTP servers with stable system clock for many years. The principle is quite simple - I replaced 14.318 MHz quartz with OCXO based circuit. Now I have to build few more servers with modern mini-ITX motherboards, however on many of them (e.g. from ASUS) I can’t find any 14.317 MHz quartz. Such frequency is a relic of original PC design and I wonder if it is used any other basic frequency in recent clock generators?
The 14.317MHz xtal was connected to the south bridge controller chip, but for recent CPUs this has gone away as has northbridge and the system clock has been integrated into the PCH (Platform Controller Hub) chip according to Wikipedia, so I suspect that if you find the clock feeding that , then you could stabilize it in that same way.
thanks,
Vladimir
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
"The power of accurate observation is commonly called cynicism by those who have not got it. »
George Bernard Shaw
Hi Vladimir,
-
Maybe you can use a DDS chip to create your 14.328 MHz signal, or
-
Do it yourself using a PLL at 45.454 kHz using 220 and 315 dividers:
10.000000 MHz / 220 = 45454.545 Hz
14.318181 MHz / 315 = 45454.545 Hz
This works because your 14.31818 MHz number is defined as 4x the 3.579545 MHz NTSC colorburst frequency,
which is defined precisely as 60 * 1000/1001 * 525/2 * 455/2,
which expands to (60 * 1000 * 3557 * 5713) / (711*13 * 2 * 2),
which reduces to 315 / 88 MHz.
So that's why 10.000000 MHz * 315 / 220 = 14.318181 MHz, exactly.
Note also that:
- 14.31818 MHz / 3 = 4.77273 MHz, the CPU clock rate for the original IBM PC
- 14.31818 MHz / 4 = 3.579545 MHz, the colorburst frequency (for PC video)
- 14.31818 MHz / 12 = 1.193182 MHz, the Intel 8253 timer clock (the historical root of all PC timekeeping)
Some of these numbers survive to the present. I'm typing this post on an XP laptop where QueryPerformanceCounter() has a Frequency.QuadPart of, you guessed it, 3579545 Hz, which is why my Win32 laptop's high-res clock has ~279 ns resolution.
For more fun with time, frequency, oscillators, and prime numbers, see:
http://www.poynton.com/PDFs/Magic_Numbers.pdf
/tvb
----- Original Message -----
From: "Vladimir Smotlacha" vs@cesnet.cz
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Tuesday, October 18, 2016 7:53 AM
Subject: [time-nuts] PC clock generator without 14.318MHz
Hello,
I have operated own NTP servers with stable system clock for many years.
The principle is quite simple - I replaced 14.318 MHz quartz with OCXO
based circuit. Now I have to build few more servers with modern mini-ITX
motherboards, however on many of them (e.g. from ASUS) I can’t find any
14.317 MHz quartz. Such frequency is a relic of original PC design and
I wonder if it is used any other basic frequency in recent clock generators?
thanks,
Vladimir
Poul-Henning,
On 10/18/2016 10:38 PM, Poul-Henning Kamp wrote:
In message ep0d0ctbrovmisvj43j57ns6smt606t3fs@4ax.com, Gary Woods writes:
On Tue, 18 Oct 2016 16:53:15 +0200, you wrote:
14.317 MHz quartz. Such frequency is a relic of original PC design
It's 4X the color subcarrier frequency in NTSC (originally U.S.)
television; rapidly becoming a dinosaur. I'm sure it was used in computers
to make color video easier. Newer boards doubtless use much faster clocks
and synthesize what the parts need.
It's 14.3181818 MHz and it has a most facinating history - if you care
for that sort of thing:
https://en.wikipedia.org/wiki/Colorburst#Rationale_for_NTSC_Color_burst_frequency
To this day, the 1.001 factor haunts us in all modern hardware and
timing designs, including the latest synchronization standards.
It's fascinating that we have been simulating several centuries into the
future to ensure that the algorithms for the synchronization will make
the 1.001 factor keep working as intended. I wrote one such simulator
being used.
Cheers,
Magnus
On 10/18/16 2:30 PM, Tom Van Baak wrote:
Hi Vladimir,
Some of these numbers survive to the present. I'm typing this post on
an XP laptop where QueryPerformanceCounter() has a Frequency.QuadPart
of, you guessed it, 3579545 Hz, which is why my Win32 laptop's
high-res clock has ~279 ns resolution.
For more fun with time, frequency, oscillators, and prime numbers,
see: http://www.poynton.com/PDFs/Magic_Numbers.pdf
and this is why clocks in film movies on TV run slightly slow<grin>..
because the film was shot at 24 fps, and it's converted to 29.97 frame
rate (in the US) by a 3:2 pulldown scheme.
I am sure that all the time nuts here notice that 0.1% rate difference.
Over a half hour TV program it adds up to almost 2 seconds of offset.
(that's just because we watch things like movies shot of counters running).
Hmm.. there's probably film footage of things with a running counter in
the scene counting tenths or hundredths of a second (sporting events,
nuclear bomb tests, etc.) I wonder if you could see that difference by
single framing something like a filmed 100 meter race where they have an
onscreen timer.
You don't have to go back very far and film cameras used mechanical
governors for speed control.. "quartz lock" is a relatively recent
addition, and as recently as 20 years ago, you had to pay extra for it
when renting camera gear.
When I was in that business, one of the things I used to do was modify
PCs so that they could be locked together - the frequency tolerance on
PCs is pretty bad, so if you have a set with a bunch of PCs they could
adjust the camera shutter phase and frame rate so you didn't get the
sync bars on one screen, but not on all, and furthermore, over a long
take, they would drift relative to each other, so even if you had them
all lined up to start...
Jim,
On 10/19/2016 12:51 AM, jimlux wrote:
On 10/18/16 2:30 PM, Tom Van Baak wrote:
Hi Vladimir,
Some of these numbers survive to the present. I'm typing this post on
an XP laptop where QueryPerformanceCounter() has a Frequency.QuadPart
of, you guessed it, 3579545 Hz, which is why my Win32 laptop's
high-res clock has ~279 ns resolution.
For more fun with time, frequency, oscillators, and prime numbers,
see: http://www.poynton.com/PDFs/Magic_Numbers.pdf
and this is why clocks in film movies on TV run slightly slow<grin>..
because the film was shot at 24 fps, and it's converted to 29.97 frame
rate (in the US) by a 3:2 pulldown scheme.
I am sure that all the time nuts here notice that 0.1% rate difference.
Over a half hour TV program it adds up to almost 2 seconds of offset.
(that's just because we watch things like movies shot of counters running).
Hmm.. there's probably film footage of things with a running counter in
the scene counting tenths or hundredths of a second (sporting events,
nuclear bomb tests, etc.) I wonder if you could see that difference by
single framing something like a filmed 100 meter race where they have an
onscreen timer.
The time-code of TV and film production runs with a frame-counter.
Now, since the 30/1.001 factor is uneven, to get things into shape the
factor is compensated using the drop-frame method. The sad thing is that
when you do the math, the drop-frame method only partially compensate
the 1.001 factor, so over a day you still drift, albeit slower. So, for
a TV-station setup, you throw a wrench into the clock machinery in order
to jam the gears into time again. Now, when you do that, all the
decoding stuff can "jump" in unexpected way, so you try to schedule it
for when you are off air or not transmitting anything important. Oh, and
we have to inherit all this into the new stuff too.
Interesting when you have to explain to them that leap seconds is
introduced at the same time, regardless of local time-scale. So,
leap-seconds would also have to be jammed-in.
Cheers,
Magnus
On Tue, 18 Oct 2016 23:36:55 +0200
Magnus Danielson magnus@rubidium.dyndns.org wrote:
To this day, the 1.001 factor haunts us in all modern hardware and
timing designs, including the latest synchronization standards.
It's fascinating that we have been simulating several centuries into the
future to ensure that the algorithms for the synchronization will make
the 1.001 factor keep working as intended. I wrote one such simulator
being used.
So, you are doing the inverse of a programmer archeologist[1]?
SCNR :-)
On a more more serious note: what exactly have you been simulating?
And how does this frequency make a difference?
Attila Kinali
[1] http://lambda-the-ultimate.org/node/4424
Malek's Law:
Any simple idea will be worded in the most complicated way.
On 10/18/16 4:25 PM, Magnus Danielson wrote:
Jim,
On 10/19/2016 12:51 AM, jimlux wrote:
On 10/18/16 2:30 PM, Tom Van Baak wrote:
Hi Vladimir,
Some of these numbers survive to the present. I'm typing this post on
an XP laptop where QueryPerformanceCounter() has a Frequency.QuadPart
of, you guessed it, 3579545 Hz, which is why my Win32 laptop's
high-res clock has ~279 ns resolution.
For more fun with time, frequency, oscillators, and prime numbers,
see: http://www.poynton.com/PDFs/Magic_Numbers.pdf
and this is why clocks in film movies on TV run slightly slow<grin>..
because the film was shot at 24 fps, and it's converted to 29.97 frame
rate (in the US) by a 3:2 pulldown scheme.
I am sure that all the time nuts here notice that 0.1% rate difference.
Over a half hour TV program it adds up to almost 2 seconds of offset.
(that's just because we watch things like movies shot of counters
running).
Hmm.. there's probably film footage of things with a running counter in
the scene counting tenths or hundredths of a second (sporting events,
nuclear bomb tests, etc.) I wonder if you could see that difference by
single framing something like a filmed 100 meter race where they have an
onscreen timer.
The time-code of TV and film production runs with a frame-counter.
Now, since the 30/1.001 factor is uneven, to get things into shape the
factor is compensated using the drop-frame method.
SO that compensates in the "big sense" so that "timecode" and "wall
clock" line up..
But when they do the original telecine, they're basically running a
30fps (interpolated from 24 fps) sequence of frames at 29.97. Over the
air, there will usually be a commercial break and they can add/drop any
arbitrary number of frames to get it to line up (should they even care
about whether the on-screen clock ticking the seconds actually lines up)
So I was thinking about something where you get a broadcast (or maybe a
video conversion on DVD/tape/online) that is a continuous piece of film.
Seems that something like 100 meter race, which lasts 10 seconds, and
will have an on screen timer to hundredths isn't quite long enough to
see the 1.001 error (and would it be one continuous shot, or would they
have edited film together from different viewpoints).
What about a filmed rocket launch with a countdown timer or similar?
they might have one continuous piece of film long enough.
Partly, its going to be limited by the magazine size of the camera: a
400 ft magazine is a bit more than 6 minutes (1 ft = 1 second in rough
terms), so that's plenty long to see the difference.
What you really want is continuous footage lasting, say, a minute, of
some event (motivating the coverage) where there's an accurate clock
visible in the scene, where the film was originally shot at 24fps, and
has been converted to video.
An interesting quest....