I stand firm that the only proper way to do this is with a 100%
deterministic architecture.
..only proper way to do what? The goal is to discipline the internal
software clock to GPS. A typical application is a database server
that is running a web e-comerse site so that transactions get
Nice toy, but the question of the necessity of a fully fledged OS for
most tasks thrown at such a small system still remains (integrated
network connectivity is a plus).
NTP isn't capable to improve the precision of a system's clock, as it
works over a heterogeneous path, which is quite
I asked this on an NTP list, got some guesses, but no knowledgeable
responses.
[]
So, running a process(es) which keep the CPU completely busy reduces the
jitter. The busier, the better. Why? I'm guessing it has something to do
with interrupt latency, but why does a busy CPU make it more
On a side note, speaking of deterministic systems, why has no one built a
GPSDO with an FPGA yet? Or an NTP server? :)
Yes, I have: I have a GPSDO entirely on a 50Kgates FPGA (Spartan3 XC3S50)
without microprocessor. GPS is the iLotus M12M and OCXO is a Morion MV201,
the DAC is... well, not
On 4/5/2012 2:51 AM, David J Taylor wrote:
Mike, have you tried FreeBSD instead? Does it show the same problems?
I have a couple of Soekris Net 4501s running FreeBSD and NTP. They don't
have much jitter, but they're a very different architecture. The machine
with the jitter is my home do
El 05/04/2012 12:20, Azelio Boriani escribió:
On a side note, speaking of deterministic systems, why has no one built a
GPSDO with an FPGA yet? Or an NTP server? :)
Oh, I've done that (an NTP server, not GPSO) in a Cyclone III FPGA. But
well... it has a Nios-II CPU and runs Linux, so I
My guess on the original question is that keeping the CPU busy puts junk into
the cache so the whole interrupt processing path takes every possible cache
miss. NTP doesn't care how fast that code is as long as it's consistent.
(Of course, you probably get a different answer, but we are
On Thu, Apr 5, 2012 at 11:11 AM, Hal Murray hmur...@megapathdsl.net wrote:
My guess on the original question is that keeping the CPU busy puts junk into
the cache so the whole interrupt processing path takes every possible cache
miss.
Cache misses are nanosecond level events not tens of
-boun...@febo.com
Date: Wed, 04 Apr 2012 22:09:14
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] NTP jitter with Linux
http://www.newegg.com/Product
: Re: [time-nuts] NTP jitter with Linux
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131663
Yep. This is what I run 24 and 7 for a number of monitoring tasks. It
has an Intel SSD. Mobo was $140 at Fry's. SSD was a Fry's special too.
It has a Nvidia ion2 (it does home theater PC
On 5 Apr, 2012, at 13:03 , shali...@gmail.com wrote:
An older laptop (Pentium M for instance) can be had for $80 or so any day of
the week, won't take much space, is completely standalone (built-in keyboard
and display, built-in battery backup) and sips power when idle, which it will
be
On Thu, Apr 5, 2012 at 1:03 PM, shali...@gmail.com wrote:
An older laptop (Pentium M for instance) can be had for $80 or so any day of
the week, won't take much space, is completely standalone (built-in keyboard
and display, built-in battery backup) and sips power when idle, which it will
I asked this on an NTP list, got some guesses, but no knowledgeable
responses.
I've got a Trimble Thunderbolt PPS source for NTP, Linux 2.6.35, on a
quad core CPU. PPS source is coming into a multiport serial card, which
/proc/interrupts shows is sharing IRQ with some inactive USB ports (IRQ
Could the CPU be reducing its clock rate when it's not being loaded? Just
a guess, most multi-core processors these days have power saving features
like that.
--
eric
On Wed, Apr 4, 2012 at 3:22 PM, Mike S mi...@flatsurface.com wrote:
I asked this on an NTP list, got some guesses, but no
Sent: Thursday, 5 April 2012 10:22 a.m.
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] NTP jitter with Linux
I asked this on an NTP list, got some guesses, but no knowledgeable responses.
I've got a Trimble Thunderbolt PPS source for NTP, Linux 2.6.35, on a quad core
That is the AMD speed step, but doesn't intel do the same thing?
Incidentally, there are hacks for linux to make it more real time, i.e.
lower latency. I never messed with them, but you find this mentioned
related to multimedia oriented distributions.
On 4/4/2012 3:53 PM, Randall Prentice
-boun...@febo.com] On Behalf
Of gary
Sent: Thursday, 5 April 2012 10:58 a.m.
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] NTP jitter with Linux
That is the AMD speed step, but doesn't intel do the same thing?
Incidentally, there are hacks for linux to make it more
On 4/4/2012 6:51 PM, Eric Williams wrote:
Could the CPU be reducing its clock rate when it's not being loaded? Just
a guess, most multi-core processors these days have power saving features
like that.
On Wed, Apr 4, 2012 at 3:22 PM, Mike Smi...@flatsurface.com wrote:
I've played around
El 05/04/2012 00:58, gary escribió:
That is the AMD speed step, but doesn't intel do the same thing?
I suppose so. In any case, under Linux you can force off the speed step
(i.e. force the CPU to a fixed clock). I did that some time ago in a
Dell server with a dual quad-core Opteron with
On 4 Apr, 2012, at 16:10 , Mike S wrote:
On 4/4/2012 6:51 PM, Eric Williams wrote:
Could the CPU be reducing its clock rate when it's not being loaded? Just
a guess, most multi-core processors these days have power saving features
like that.
On Wed, Apr 4, 2012 at 3:22 PM, Mike
On 4/4/2012 10:41 PM, Steve . wrote:
breaking the 1pps down as far as 10micro seconds,The
most obviously problem is that you are trying to use an inaccurate clock
source(the pc)
Your reply ignores the simple fact that it _does_ track within a couple
of microseconds, as long as the processor
It doesn't matter how fast the CPU clock rate is because you are not
dealing with a simple rate monotonicity. There are far too many
inconstancies in a PC to properly apply simple O(n) algorithms.
Your reply ignores the simple fact that it _does_ track within a couple of
microseconds, as long as
I built a small form factor PC using the Intel D525.
http://ark.intel.com/products/49490/Intel-Atom-processor-D525-%281M-Cache-1_80-GHz%29
If you look at the features (or lack thereof!), it lacks turbo boost
and enhanced Intel Speed Step technology. So you may not have to
resort to using a
On Thu, Apr 5, 2012 at 12:17 AM, gary li...@lazygranch.com wrote:
I built a small form factor PC using the Intel D525.
http://ark.intel.com/products/49490/Intel-Atom-processor-D525-%281M-Cache-1_80-GHz%29
If you look at the features (or lack thereof!), it lacks turbo boost and
enhanced
On Wed, Apr 4, 2012 at 9:17 PM, gary li...@lazygranch.com wrote:
I built a small form factor PC using the Intel D525.
http://ark.intel.com/products/49490/Intel-Atom-processor-D525-%281M-Cache-1_80-GHz%29
I did the same thing. They work well and even if you have a free
quad core PC in a
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131663
Yep. This is what I run 24 and 7 for a number of monitoring tasks. It
has an Intel SSD. Mobo was $140 at Fry's. SSD was a Fry's special too.
It has a Nvidia ion2 (it does home theater PC streaming at times.] USB
3. Gigabit
On Wed, Apr 4, 2012 at 9:22 PM, Steve . iteratio...@gmail.com wrote:
If the architecture has cache or wait states, it is still subject to be a
moving target. I'm naturally skeptical on all architectures that have
multiple channels, show me an architecture with cache or waits states and
i'll
As a rule of thumb, any general purpose architecture will be less
effective at a specific task than a specially designed one. That applies
more and more to the modern way of solving tasks: software.
The PC is one of the classical examples of GPA, and as such it is best
to know its limitations,
Indeed, I'm looking forward to getting a few raspberry pis to play with. NTP is
but one of the interesting time related projects possible with a $35(us) Linux
platform. The system has a number of i/o pins directly exposed that will make
interfacing interesting.
On a side note, speaking of
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