Hi Nick,
I've got a project along those lines that I've been hacking on for the past
three years or so, and always meaning to do a thorough writeup on. I'm more
of a software than hardware guy, so the heart of it is a Taijiuino Due (a
weird Chinese clone of the Arduino Due, so an 84MHz ATSAM3X8E,
The 6-7us of latency in this discussion does not involve the network path. In
this regard network latency is fairly well addressed with hardware
timestamping, although trying to get readings across the clock domains looses
dozens of nanos of precision. In this discussion, the 6-7us of latency
o
On Wed, 1 Nov 2017 10:15:43 -0700
Denny Page wrote:
> > 6-10µs is the interrupt latency of linux on ARM SoC. I guess, to get
> > below that you'd have to tweak the kernel a bit. Which should not
> > be that difficult. Definitly simpler than writing your own IP and NTP
> > stack from scratch.
>
>
On Wed, 1 Nov 2017 13:11:00 -0400
wrote:
> I am trying to beat existing products like the Dallas DS3231 and Micro
> Crystal RV-8803-C7-32.768kHz-3PPM-TA-QC, which use (I think) a similar
> strategy. I’m hoping I can beat them by using more accurate temp tensing,
> longer and more exhaustive ca
On 11/1/17 12:13 PM, Adrian Godwin wrote:
How do those compare with vectron's part : ?
https://www.vectron.com/products/ocxo/mx-503.htm
That part is interesting, but the phase noise (-124 dBc @ 100 Hz) isn't
particularly impressive compared to a middle of the road OCXO (-155dBc
at 100Hz)
Regarding spread spectrum issues:
You might be lucky to find (or have) SSCG implementation that is reasonably
stable. I suspect most are - because it is easy to generate hershey kiss
spectrum based on SM, LUT or some sort of multi-level LFSRs. I don't know what
this means - these are some ran
Hi
> On Nov 1, 2017, at 1:11 PM, tn...@joshreply.com wrote:
>
>> While crystal curves are indeed cubic, there are higher order terms in
>> the curve. The “why” is something people get to write papers on. If you
>> are trying to compensate to tight specs, you will see all sorts of
>> stuff. It
> On Nov 01, 2017, at 05:39, Attila Kinali wrote:
>
> 6-10µs is the interrupt latency of linux on ARM SoC. I guess, to get
> below that you'd have to tweak the kernel a bit. Which should not
> be that difficult. Definitly simpler than writing your own IP and NTP
> stack from scratch.
Just tweak
tn...@joshreply.com said:
> I am trying to build the most accurate fee running, low power time base I can.
> I am trying to beat existing products like the Dallas DS3231 and Micro
> Crystal RV-8803-C7-32.768kHz-3PPM-TA-QC, which use (I think) a similar
> strategy. Iâm hoping I can beat them by
How do those compare with vectron's part : ?
https://www.vectron.com/products/ocxo/mx-503.htm
There's also this patent.
http://www.google.sr/patents/US20020005765
I don't really know if that's valid - it seems to propose something similar
to the numerically-compensated oscillator in my rather
Hoi Leo,
On Wed, 1 Nov 2017 15:35:46 +
Leo Bodnar wrote:
> > From: Attila Kinali
> > What you should do is basically system identification and adaptive control.
>
> Thanks for your advice, Attila, I am going to google this tonight. This is
> exciting!
Before you dive into sys-id and ad
>While crystal curves are indeed cubic, there are higher order terms in
>the curve. The “why” is something people get to write papers on. If you
>are trying to compensate to tight specs, you will see all sorts of
>stuff. It is not at all uncommon to see >9th order curves residual curves.
>Indee
> From: Attila Kinali
> What you should do is basically system identification and adaptive control.
Thanks for your advice, Attila, I am going to google this tonight. This is
exciting!
Leo
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Antenna is a Tallysman TW4722.
I'll try a different antenna later. If nothing else, right now I've got regular
dropouts for failsafe testing...
But I feel a better solution is a reliable holdover capability, which I should
have anyway for failsafe.
Thanks,
Michael
On 01/11/2017 10:22 AM,
One can minimize temperature change which affects things like
regulated voltages, CMOS transition points for those converting
sine to TTL with gates, etc. in addition to the oscillators.
The November issue of Nuts and Volts Magazine has an article on an
Arduino based PID controller which might i
Hi
Ok, local RF interference sounds like a significant part of the problem. I
would
suggest that swapping antennas might make sense. Not all “super interference
rejecting” antennas are created equal.
Bob
> On Nov 1, 2017, at 9:55 AM, MLewis wrote:
>
> I wish.
>
> It's using GLO and GPS now
I wish.
It's using GLO and GPS now, yet gets reception dropouts.
That's why I'm hoping to eventually get the firmware update that will
add GAL to the mix.
I had anticipated reception issues, which is why I went with the M8T for
its sensitivity, multi-constellation and it's a timing module so
Hi
> On Nov 1, 2017, at 9:17 AM, jimlux wrote:
>
> On 11/1/17 6:01 AM, Bob kb8tq wrote:
>> Hi
>> Unfortunately not all TCXO’s are created equal. It depends a bit on the
>> original intended use. I’d bet it also depends a bit on the original target
>> price. Perturbations (frequency jumps) over
On 11/1/17 6:01 AM, Bob kb8tq wrote:
Hi
Unfortunately not all TCXO’s are created equal. It depends a bit on the
original intended use. I’d bet it also depends a bit on the original target
price. Perturbations (frequency jumps) over temperature are one “feature”
that might be present. Hysteresis
Hi
> On Oct 31, 2017, at 11:33 PM, Leo Bodnar wrote:
>
>> From: Bob kb8tq
>> Working all this back into a holdover spec in an unknown temperature
>> environment is not at all easy.
>> Bob
>
>
> This is true, it is too easy to multiply figures from the datasheet and then
> start believing in
Hi
Unfortunately not all TCXO’s are created equal. It depends a bit on the
original intended use. I’d bet it also depends a bit on the original target
price. Perturbations (frequency jumps) over temperature are one “feature”
that might be present. Hysteresis at half the temperature spec is anoth
Hi
For NTP levels of accuracy Glonas is quite fine. Combining that with GPS should
get you a pretty good “time source” even under your extreme conditions.
Bob
> On Oct 31, 2017, at 11:14 PM, MLewis wrote:
>
> I'm stuck with a near ground level antenna site (~16" above grade?), with
> half a s
On Tue, 31 Oct 2017 22:13:01 -0700
Denny Page wrote:
> Depends upon the results you are trying to achieve. Using Linux pretty
> much guarantees that your server clock will be off by 6-10us, with
> substantial variance. Even with a good nic that supports hardware
> timestamping, the variance will
On Wed, 1 Nov 2017 04:06:06 +
Leo Bodnar wrote:
> > From: Attila Kinali
> > Basically, all you have to do is use an SBC that runs linux and has
> > a GPIO with an interrupt to act as a PPS input. Attach a GPS receiver
> > and you are almost done. The cheapest option are probably the i.MX233
Depends upon the results you are trying to achieve. Using Linux pretty much
guarantees that your server clock will be off by 6-10us, with substantial
variance. Even with a good nic that supports hardware timestamping, the
variance will increase substantially as you go off box (spread spectrum is
> From: Attila Kinali
> Basically, all you have to do is use an SBC that runs linux and has
> a GPIO with an interrupt to act as a PPS input. Attach a GPS receiver
> and you are almost done. The cheapest option are probably the i.MX233
> based ones (go as low as €20).
Thank you, Attila, this sou
> I'm intending to add a "precision" (well, precision to the Pi world) RTC to
> my Pi 3 to use for a holdover source when it hasn't got PPS from the GPS
> module.
> An RTC that +/- 3 PPM over 24 hours would be great for holdovers of one to
> 20 minutes.
Run some experiments to collect some
> From: Bob kb8tq
> Working all this back into a holdover spec in an unknown temperature
> environment is not at all easy.
> Bob
This is true, it is too easy to multiply figures from the datasheet and then
start believing in them.
We did extensive testing of real units in real life before com
I'm stuck with a near ground level antenna site (~16" above grade?),
with half a sky view (thankfully to the SSE), less some low blocking
buildings with regular mutlipath, plus multipath bouncing off a taller
building to the SE that bounces sats from the NW at me from low over the
Bering Strait
On 10/31/17 1:47 PM, Bob kb8tq wrote:
HI
TCXO is a very loosely defined term. A part that does +/- 5 ppm -40 to +85C
is a TCXO. A part that does +/- 5x10^-9 over 0 to 50C may also be a TCXO.
Dividing the total deviation of either one by the temperature range to come
up with a “delta frequency p
Hi
Under what conditions would you expect to loose GPS? I seem to be able to
do just fine sitting in an armchair here in the family room. That’s hardly a
fancy setup.
Bob
> On Oct 31, 2017, at 10:27 PM, MLewis wrote:
>
> I'm intending to add a "precision" (well, precision to the Pi world) RT
I'm intending to add a "precision" (well, precision to the Pi world) RTC
to my Pi 3 to use for a holdover source when it hasn't got PPS from the
GPS module.
On 31/10/2017 10:04 PM, Chris Caudle wrote:
On Tue, October 31, 2017 7:19 pm, MLewis wrote:
...the "better" quality RTCs seem to be DS32
I don't know of any "non-historic" NTP implementation that even attempts to
drift correct the RTC clock.
Now, the RTC clock is useful to set the time at boot before ntpd gets
started.
Tim N3QE
On Tue, Oct 31, 2017 at 8:19 PM, MLewis wrote:
> If one is building a GPS disciplined NTP Stratum 1 s
On Tue, October 31, 2017 7:19 pm, MLewis wrote:
> ...the "better" quality RTCs seem to be DS3231 based
> How does one translate that into an expected 24 hour holdover?
For the RTC, or for an NTP server? If the NTP server is running it will
not make a difference, modern operating systems do not us
At the moment, my plan is to not support hold-over at all. If GPS doesn’t have
a fix and I’m not getting PPS pulses, I intend to either jump immediately to
stratum 16 or just not respond.
> On Oct 31, 2017, at 1:03 PM, Attila Kinali wrote:
>
> Hoi Leo,
>
> On Sat, 28 Oct 2017 11:14:08 +0100
>
HI
> On Oct 31, 2017, at 8:19 PM, MLewis wrote:
>
> If one is building a GPS disciplined NTP Stratum 1 server from a Pi or
> Beaglebone, the "better" quality RTCs seem to be
>
> DS3231 based (DallasSemi/Maxim), Accuracy ±2ppm from 0°C to +40°C, ±3.5ppm
> from -40°C to +85°C
>
> or
>
> NXP:
If one is building a GPS disciplined NTP Stratum 1 server from a Pi or
Beaglebone, the "better" quality RTCs seem to be
DS3231 based (DallasSemi/Maxim), Accuracy ±2ppm from 0°C to +40°C,
±3.5ppm from -40°C to +85°C
or
NXP:
PCF2127AT: ±3 ppm from -15 °C to +60 °C
PCF2127T: ±3 ppm from
On Tue, 31 Oct 2017 21:03:05 +
Leo Bodnar wrote:
> The goal was maximum throughput with minimum time offset.
> Maximum throughput eventually ended up as "fully saturated full-duplex
> 100BASE-TX" and minimum time offset as "below 1 microsecond"
> There was nothing on the market below £2-3k t
> From: Attila Kinali
> True. An NTP server does not need to measure time better than 100ns or so.
> 10ns is probably more than good enough. But then, this raises the question
> what your performance metric is that you optimize for?
The goal was maximum throughput with minimum time offset.
Maximu
HI
TCXO is a very loosely defined term. A part that does +/- 5 ppm -40 to +85C
is a TCXO. A part that does +/- 5x10^-9 over 0 to 50C may also be a TCXO.
Dividing the total deviation of either one by the temperature range to come
up with a “delta frequency per degree” number would be a mistake.
Hoi Leo,
On Sat, 28 Oct 2017 11:14:08 +0100
Leo Bodnar wrote:
> > From: Attila Kinali
> > Can you tell a little bit how your device looks like on the inside?
>
> GPS is a Ublox. MCU is Cortex-M7 and does not run any OS - just main loop
> with prioritised interrupts. Network stack is hand-ma
> Le 29 oct. 2017 à 11:29, Leo Bodnar a écrit :
>
> If you are making an open source thing you might want to use Laureline NTP
> http://partiallystapled.com/pages/laureline-gps-ntp-server.html as a starting
> point or as a performance yardstick. I have never seen one so can't comment
> on ho
Back to back with 100Mb is good, particularly for latency tests, but you’ll
need a switch for general testing. FWIW, an otherwise idle switch generally has
very consistent latency, and if both ports are at 100Mb, it is symmetric. Also,
with any kind of managed switch you can easily monitor traff
I think my test rig is likely to be a pair of units connected with a crossover
cable, with test firmware on one to act as a fake client, and using spare GPIOs
on test points to measure latency and the like with a scope. I don’t have the
wherewithal to try and gauge the timing of switches, and of
With 1588 switch architecture counts as well because you have two major classes
of switch, blocking and non blocking plus buffering etc.
Most 'enterprise' switches once the flow is set up directly forward frames from
the ingress port to the egress port each of which also tends to have a fairly
> From: Nick Sayer
> I believe I’m going to start with one of my GPS module breakouts and an E70
> XPlained development board. From a hardware perspective, I expect that to be
> reasonably close to what the final hardware will be (the one thing I would
> guess would change would be perhaps swap
I built a couple of NTP time servers around this board:
https://www.olimex.com/Products/ARM/ST/STM32-E407/open-source-hardware
which supports IEEE1588. It also acts as a PTP source on the LAN. It is
part of the IPv6 ntp pool and is currently serving about 1000 requests
per minute. It uses a cus
That looks and sounds very, very much like what I want to do.
Thank you very much for your testing suggestions. When it comes time, I had
indeed planned on adding it to the NTP pool if for no other reason than to
contribute to the cause (but also for testing).
I believe I’m going to start with
> From: Attila Kinali
> Can you tell a little bit how your device looks like on the inside?
GPS is a Ublox. MCU is Cortex-M7 and does not run any OS - just main loop with
prioritised interrupts. Network stack is hand-made.
I don't use saw-tooth correction in this device because +-11ns is not
> On Oct 26, 2017, at 19:29, Chris Caudle wrote:
>
> On Thu, October 26, 2017 7:38 pm, Denny Page wrote:
>> If you are going to do PTP with ptp4l, or NTP with Chrony, you are going
>> to want hardware timestamping support on the ethernet phy.
>
> Or the MAC. The processor used on BeagleBone Bl
Hoi Leo,
On Fri, 27 Oct 2017 20:27:53 +0100
Leo Bodnar wrote:
> Last year I have designed an NTP server with sub-microsecond turnaround
> accuracy/jitter at fully saturated 100K+ packets/sec traffic (full 100Mb wire
> speed) that costs just £250 from stock.
> Its holdover performance on signal
Hi Nick,
Last year I have designed an NTP server with sub-microsecond turnaround
accuracy/jitter at fully saturated 100K+ packets/sec traffic (full 100Mb wire
speed) that costs just £250 from stock.
Its holdover performance on signal loss is in the order of 4-5ms/day.
https://store.uputronics.co
On Thu, October 26, 2017 7:38 pm, Denny Page wrote:
> If you are going to do PTP with ptp4l, or NTP with Chrony, you are going
> to want hardware timestamping support on the ethernet phy.
Or the MAC. The processor used on BeagleBone Black has timestamping in
the MAC. Not quite as accurate as sta
On Thu, October 26, 2017 5:58 pm, Bob kb8tq wrote:
> Why go to the green?
Cheaper.
> Just go with one of these Pocket Beagles I have
> sitting here wondering what to do with them.
Pocket Beagles do not have Ethernet. How are you going to make a network
time server from a board with no network?
Hi
I suspect that once you find a group of chips that do have 1588 embedded in
them that
digging into all the nasty details will take a bit. Time stamping to a 1 ms
resolution might
not be a very helpful thing ….. There are ex-Freescale / now NXP devices that
do have
pretty good 1588 in them. I
If you are going to do PTP with ptp4l, or NTP with Chrony, you are going to
want hardware timestamping support on the ethernet phy. I would view this as
one of the principal concerns in choosing a system.
I’m not sufficiently familiar with Beagles… do any of them support hardware
timestamping?
Hi
Why go to the green? Just go with one of these Pocket Beagle’s I have sitting
here wondering what to do with them. They were just a bit under $20 when I
picked them up. I doubt the price will climb over time …… Indeed you could
get two Pi Zero W’s for the pice of the Pocket Beagle. Lash an int
On 26/10/17 22:11, Chris Caudle wrote:
The processor you mentioned has a Cortex-M7 at 300MHz. has a
Cortex-A8 running at 1GHz plus a Cortex-M processor available as a
coprocessor. Peripheral set is pretty comparable, and you can buy BBB at
retail for $50 which gets you the faster higher cl
On Wed, October 25, 2017 7:53 pm, Nick Sayer via time-nuts wrote:
> I am considering a new project based on its cousin, the ATSAME70.
What is a reasonable cost target for that at the volumes you could
produce? Coming up with something that is a better value than BeagleBone
Black at any kind of ho
Hi
So, get it up and running on the 1588 hardware built into one of these “all in
one”
MCU’s should be possible. Note the absence of words like easy or
straightforward :)
Bob
> On Oct 26, 2017, at 12:45 PM, Chris Caudle wrote:
>
> On Thu, October 26, 2017 9:40 am, Bob kb8tq wrote:
>> Since
On Thu, October 26, 2017 9:40 am, Bob kb8tq wrote:
> Since time stamping hardware does exist for 1588, why not simply put the
> effort into folding that into NTP?
According to the Chrony project web page chronyd already includes support
for that.
See "NTP timestamping" section:
https://chrony.tuxf
Hi
Since time stamping hardware does exist for 1588, why not simply put the effort
into
folding that into NTP? Then you have a “generic” solution that addresses a lot
of the
ambiguity a wide range of cases. It shows up in many of the low end micro’s so
it’s
not just a “big box only” solution.
Yo Nick!
On Wed, 25 Oct 2017 17:53:46 -0700
Nick Sayer via time-nuts wrote:
> This may be a fool’s errand, certainly, but looking at it from here,
> I would think that such a design might offer accuracy in the
> microsecond range,
I'm looking at 6 Raspberry Pi's right now, each with a different
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