[time-nuts] : L1 GPS timing signal(s) into local time on computer(s)

Willy Willemse willy.willemse at telenet.be
Sun Aug 19 15:21:50 EDT 2012


Sarah,

If you want to filter in ebay, you can use a"-" for a subject that you don't
want to see. It is the same syntax as you can use in a browser.

Regards,

Willy

-----Oorspronkelijk bericht-----
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time-nuts-request at febo.com
Verzonden: zondag 19 augustus 2012 19:07
Aan: time-nuts at febo.com
Onderwerp: time-nuts Digest, Vol 97, Issue 48

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Today's Topics:

   1. Re: L1 GPS timing signal(s) into local time on	computer(s)
      (Sarah White)
   2. Modern motherboard with RS232 port (Stan, W1LE)
   3. Re: L1 GPS timing signal(s) into local time on	computer(s)
      (KD0GLS)
   4. Embedded NTP servers? (Michael Tharp)
   5. Re: Modern motherboard with RS232 port (Chris Albertson)


----------------------------------------------------------------------

Message: 1
Date: Sun, 19 Aug 2012 10:41:39 -0400
From: Sarah White <kuzetsa at gmail.com>
To: time-nuts at febo.com
Subject: Re: [time-nuts] L1 GPS timing signal(s) into local time on
	computer(s)
Message-ID: <5030FB23.7040508 at gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Ken:

>From what I've read, most GPS modules which output PPS, the NMEA
sentence has the timestamp of the next, upcoming pulse. Regardless of
how the NMEA or other time data is, the PPS itself is only a guarantee
"this is the boundary for a second" and NTP documentation typically
recommends a second reference clock to "number the seconds" anyway.

Everyone:

Thanks everyone. I got many responses which confirm my initial
conclusions. I had trouble locating a GPS thunderbolt on ebay because
there is an HTC phone with "thunderbolt" in the name. (I got a few hits
for the GPS module, but there is no way to filter out "phones" or I
might just be bad at operating ebay)

uhm... yeah. As someone pointed out. It is a total nightmare to figure
out which direction my GPS time is wandering, and finding the correct
offset. I'm just gonna give up on this USB module, and get a real one
with PPS

Also, I really hate google's new "shopping" experience. They started
listing less content, and now push content from stores which charge 2-3
times as much.

As far as existing hardware goes, I don't have any slots free in my
desktop for a serial board...

Despite the new "google shopping" headache, I was able to determine that
many "older" computers from the windows XP era which still have serial
ports, and are available refurbished from walmart of all the crazy
places. (most of the time, better price than the ones being pushed by
google shopping, and even have XP installed and a 1 year warranty)

So no problem. I can source a suitable machine to run NTP, and for less
than $200, guaranteed.

Will probably be using gentoo linux, as the default configuration does
NOT expect you to run any specific kernel. I can easily recompile
anything I need without breaking unusual, unforeseen dependencies.
(doesn't hurt that I've been using gentoo since the stage1 install was
preferred, all the way back to the GCC 2.x era)

I'm really aiming to run a server which ONLY runs NTP, and at most 1 or
two other daemons (light duty on those)

Thanks so much everyone.

On 8/19/2012 7:11 AM, Ken Duffill wrote:
> Just one further question.
> 
> When the pps input triggers, so my linux box knows a second has just
> ticked; is the time of that second the one the NMEA sentence has just
> sent, or will send next?
> 
> Or to put it another way, when I receive an NMEA sentence is this the
> current time (as was when the sentence was constructed) or the time at
> the next PPS 'tick'?
> 
> Thanks in advance.
> 
> KenD
> 
> On 19/08/12 11:23, Bill Dailey wrote:
>> I will jump in a bit.  I, and many have been right where you are.  You
>> are correct...USB is a no go for accurate time.  Same on windows.  So
>> you need a Linux box with serial port.  Anything from a Beaglebone,
>> pandabox...or pc will work.  You certainly need a gps with a pulse per
>> second output (most have) and you can wire that up to the appropriate
>> line on the serial cable or send to the target computer via gpio pin. 
>> The pps thing is fairly simple really.   If you are receiving gps data
>> via serial connection it takes a variable amount of time to get each
>> status report from the gps...list time etc etc in text format and
>> sends it repeatedly.  This gets ntp to within a second or some
>> fraction thereof...the pps part refines that..no text or anything...
>> Just a one pulse per second separate from the gps info that acts as a
>> exclamation point to tell ntp "right here is the actual start of the
>> second!" alone the pps wouldn't be useful for time but with the time
>> info ntp already has from the nmea sentences it is priceless for
>> really precise time.   That's about it.  Once you have gps and pps
>> configured on Linux you should be in the sub 5 microsecond range.  It
>> gets tricky getting better than that and you have to Ntpns and really
>> worry about hardware issues that affect precision (system clock
>> stability etc) but it can be done.
>>
>> Doc
>> KX0O
>>
>> Sent from my iPad
>>
>> On Aug 18, 2012, at 11:25 PM, Sarah White <kuzetsa at gmail.com> wrote:
>>
>>> Hi, this is my first post.
>>>
>>> First off. Windows 7 USB connection to the GPS (no serial ports / modern
>>> computer) and I'm pretty sure that is my main problem.
>>>
>>> Past few months, I've been trying to figure out my timing issues. Lots
>>> of reading & trying to figure out how to best configure everything. I'm
>>> typically still off (randomly) by 20-100 miliseconds. I'd like to at
>>> least get to within 50 microseconds (nanoseconds would be wonderful)
>>>
>>> 1) I need a computer with a serial port. The curent GPS module I'm using
>>> is INTERNALLY RS232 --> USB converter, and recognized by my windows 7
>>> computer as: "Prolific USB-to-Serial Comm Port (COM3)" ... the latency
>>> and jitter is horrible, and both are seemingly random.
>>>
>>> 2) I need to run my stratum 1 clock (connected to the stratum 0 time
>>> source via old-school RS232 serial) on linux or a form of BSD with
>>> support for kernel timestamps, and a version of NTP with a driver to
>>> supports my reference clock... points 1 and 2 seem fine.
>>>
>>> 3) I'm clueless about mounting an antenna, running cable, grounding /
>>> lightning protection, etc... Really want an easy to install one.
>>>
>>> For software, I've used 4.2.6 (stable / production) as well as 4.2.7
>>> (dev version) NTP and haven't been able to tell any difference.
>>> Just using the generic NMEA driver / this is a no-name cheapo SIRF
>>> module.
>>>
>>> Also, trying to wrap my head around these:
>>>
>>> http://linuxpps.org/wiki/index.php/LinuxPPS_installation
>>> http://linuxpps.org/wiki/index.php/LinuxPPS_NTPD_support
>>>
>>> And here is where I give up. As the subject line suggests:
>>>
>>> HELP!!! I'd like to convert L1 GPS timing signal(s) into local time on
>>> computer(s)
>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
> 
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.




------------------------------

Message: 2
Date: Sun, 19 Aug 2012 10:42:10 -0400
From: "Stan, W1LE" <stanw1le at verizon.net>
To: time-nuts at febo.com
Subject: [time-nuts] Modern motherboard with RS232 port
Message-ID: <5030FB42.8030501 at verizon.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hello The Net,

For your consideration:

The INTEL model DN2800mt ITX mother board uses a ATOM CPU and
draws about 11 watts of AC power when configured as:
(I have not measured DC power yet.)

30 GB OCZ Nocti mSATA solid state drive,
WIN7 pro, 64 bit, USB keyboard and mouse
APEX MI-0008 case.

Also has:
parallel port available on mother board, you extend to a connector
RS232 serial port available on mother board, you extend to a connector
a single DC power supply from 11 to 19 V DC.
1 each PCIe expansion port, I will use with a premium 4 channel sound card
SATA ports available for HDD/SDD,
USB ports are available,
Motherboard sound, and Gigalan.

I have not played with NTP, (yet), but it sounds like a decent time nut 
technical challenge.

My application is for a remote site with only 13V DC power available 
from PV/batteries.
Then use fiber ethernet to get off site.

The INTEL website would have further details.

Stan, W1LE    Cape Cod   FN41sr




ZZZZz




------------------------------

Message: 3
Date: Sun, 19 Aug 2012 10:18:34 -0500 (CDT)
From: KD0GLS <kd0gls at mninter.net>
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] L1 GPS timing signal(s) into local time on
	computer(s)
Message-ID: <AE1D2790-AF2B-40FC-88D8-F13A61D77B42 at mninter.net>
Content-Type: text/plain;	charset=us-ascii

In my experience (which is admittedly less than that of many others here)
the time reported is that of the PPS pulse that just happened, and the
documentation usually bears that out. There's a real-time clock running
inside the receiver that is synchronized to the PPS. At the top of the
second, the PPS is output and the RTC increments. Some number of
milliseconds later, that RTC time value is output, which is the "current"
time, not that of the next pulse. That's certainly the way the Motorola M12+
Timing receiver (Motorola binary mode) and all of the SiRFstar-based NMEA
navigation receivers I've used work.

Beware of the situation where a cold-started receiver hasn't yet acquired
the UTC offset portion of the almanac and will report time some number of
seconds different than UTC. The SiRF receivers are especially misleading, as
they can be off by just one or two seconds depending on when their firmware
was built. They are programmed with default offset values that were valid at
the time of their manufacture. In one case I had, it was sometimes off by
one second, sometimes not. After June 30, 2012, it was now sometimes off by
two seconds, and then I knew what was going on. The M12+ has a default
offset of zero, which I find much more sane. It reports GPS time (a whopping
16 seconds different) until the UTC offset is received. 

Sent from my iPod

On Aug 19, 2012, at 9:42, Sarah White <kuzetsa at gmail.com> wrote:

> Ken:
> 
> From what I've read, most GPS modules which output PPS, the NMEA
> sentence has the timestamp of the next, upcoming pulse. Regardless of
> how the NMEA or other time data is, the PPS itself is only a guarantee
> "this is the boundary for a second" and NTP documentation typically
> recommends a second reference clock to "number the seconds" anyway.
> 
> Everyone:
> 
> Thanks everyone. I got many responses which confirm my initial
> conclusions. I had trouble locating a GPS thunderbolt on ebay because
> there is an HTC phone with "thunderbolt" in the name. (I got a few hits
> for the GPS module, but there is no way to filter out "phones" or I
> might just be bad at operating ebay)
> 
> uhm... yeah. As someone pointed out. It is a total nightmare to figure
> out which direction my GPS time is wandering, and finding the correct
> offset. I'm just gonna give up on this USB module, and get a real one
> with PPS
> 
> Also, I really hate google's new "shopping" experience. They started
> listing less content, and now push content from stores which charge 2-3
> times as much.
> 
> As far as existing hardware goes, I don't have any slots free in my
> desktop for a serial board...
> 
> Despite the new "google shopping" headache, I was able to determine that
> many "older" computers from the windows XP era which still have serial
> ports, and are available refurbished from walmart of all the crazy
> places. (most of the time, better price than the ones being pushed by
> google shopping, and even have XP installed and a 1 year warranty)
> 
> So no problem. I can source a suitable machine to run NTP, and for less
> than $200, guaranteed.
> 
> Will probably be using gentoo linux, as the default configuration does
> NOT expect you to run any specific kernel. I can easily recompile
> anything I need without breaking unusual, unforeseen dependencies.
> (doesn't hurt that I've been using gentoo since the stage1 install was
> preferred, all the way back to the GCC 2.x era)
> 
> I'm really aiming to run a server which ONLY runs NTP, and at most 1 or
> two other daemons (light duty on those)
> 
> Thanks so much everyone.
> 
> On 8/19/2012 7:11 AM, Ken Duffill wrote:
>> Just one further question.
>> 
>> When the pps input triggers, so my linux box knows a second has just
>> ticked; is the time of that second the one the NMEA sentence has just
>> sent, or will send next?
>> 
>> Or to put it another way, when I receive an NMEA sentence is this the
>> current time (as was when the sentence was constructed) or the time at
>> the next PPS 'tick'?
>> 
>> Thanks in advance.
>> 
>> KenD
>> 
>> On 19/08/12 11:23, Bill Dailey wrote:
>>> I will jump in a bit.  I, and many have been right where you are.  You
>>> are correct...USB is a no go for accurate time.  Same on windows.  So
>>> you need a Linux box with serial port.  Anything from a Beaglebone,
>>> pandabox...or pc will work.  You certainly need a gps with a pulse per
>>> second output (most have) and you can wire that up to the appropriate
>>> line on the serial cable or send to the target computer via gpio pin. 
>>> The pps thing is fairly simple really.   If you are receiving gps data
>>> via serial connection it takes a variable amount of time to get each
>>> status report from the gps...list time etc etc in text format and
>>> sends it repeatedly.  This gets ntp to within a second or some
>>> fraction thereof...the pps part refines that..no text or anything...
>>> Just a one pulse per second separate from the gps info that acts as a
>>> exclamation point to tell ntp "right here is the actual start of the
>>> second!" alone the pps wouldn't be useful for time but with the time
>>> info ntp already has from the nmea sentences it is priceless for
>>> really precise time.   That's about it.  Once you have gps and pps
>>> configured on Linux you should be in the sub 5 microsecond range.  It
>>> gets tricky getting better than that and you have to Ntpns and really
>>> worry about hardware issues that affect precision (system clock
>>> stability etc) but it can be done.
>>> 
>>> Doc
>>> KX0O
>>> 
>>> Sent from my iPad
>>> 
>>> On Aug 18, 2012, at 11:25 PM, Sarah White <kuzetsa at gmail.com> wrote:
>>> 
>>>> Hi, this is my first post.
>>>> 
>>>> First off. Windows 7 USB connection to the GPS (no serial ports /
modern
>>>> computer) and I'm pretty sure that is my main problem.
>>>> 
>>>> Past few months, I've been trying to figure out my timing issues. Lots
>>>> of reading & trying to figure out how to best configure everything. I'm
>>>> typically still off (randomly) by 20-100 miliseconds. I'd like to at
>>>> least get to within 50 microseconds (nanoseconds would be wonderful)
>>>> 
>>>> 1) I need a computer with a serial port. The curent GPS module I'm
using
>>>> is INTERNALLY RS232 --> USB converter, and recognized by my windows 7
>>>> computer as: "Prolific USB-to-Serial Comm Port (COM3)" ... the latency
>>>> and jitter is horrible, and both are seemingly random.
>>>> 
>>>> 2) I need to run my stratum 1 clock (connected to the stratum 0 time
>>>> source via old-school RS232 serial) on linux or a form of BSD with
>>>> support for kernel timestamps, and a version of NTP with a driver to
>>>> supports my reference clock... points 1 and 2 seem fine.
>>>> 
>>>> 3) I'm clueless about mounting an antenna, running cable, grounding /
>>>> lightning protection, etc... Really want an easy to install one.
>>>> 
>>>> For software, I've used 4.2.6 (stable / production) as well as 4.2.7
>>>> (dev version) NTP and haven't been able to tell any difference.
>>>> Just using the generic NMEA driver / this is a no-name cheapo SIRF
>>>> module.
>>>> 
>>>> Also, trying to wrap my head around these:
>>>> 
>>>> http://linuxpps.org/wiki/index.php/LinuxPPS_installation
>>>> http://linuxpps.org/wiki/index.php/LinuxPPS_NTPD_support
>>>> 
>>>> And here is where I give up. As the subject line suggests:
>>>> 
>>>> HELP!!! I'd like to convert L1 GPS timing signal(s) into local time on
>>>> computer(s)
>>>> 
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts at febo.com
>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>> and follow the instructions there.
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>> 
>> 
>> 
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.



------------------------------

Message: 4
Date: Sun, 19 Aug 2012 11:21:21 -0400
From: Michael Tharp <gxti at partiallystapled.com>
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: [time-nuts] Embedded NTP servers?
Message-ID: <50310471.1090102 at partiallystapled.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Greetings nuts,

All this recent NTP discussion has me thinking about a dedicated NTP 
server again. The usual solution is to use commodity hardware of some 
persuasion (PC, mini-itx or even ARM) running ntpd, but I'm thinking we 
can do better. The only reason a full ntpd is needed is for its software 
PLLs that measure and compensate for deficiencies in the local 
oscillator. But if that local oscillator is replaced by a disciplined 
10MHz clock, and a coincident pulse-per-second and NMEA from the GPSDO 
fed in, then a reasonably fitted microcontroller should do the trick.

I happen to have a Ethernet-enabled widget I put together for another 
project as a kind of drop-in module, built on a PIC18F66J60 which has a 
built-in 10mbit Ethernet controller. The problem with it seems to be 
relatively poor and unpredictable packet servicing latency. Usually 
pings are 1.02ms but with some significant deviation. I imagine a lot of 
the deficiencies with this arrangement come from the vendor-supplied IP 
stack, which is not latency-optimized, but also the 10mbit link 
contributes some "quantization" type problems. Microchip also makes a 
100mbit-capable standalone controller, ENC624J600. I'd probably use that 
and pair it with any 72MHz ARM microcontroller. The micro would be 
clocked by a (multiplied) 10MHz disciplined input and the 
pulse-per-second would come in on a "input capture" channel that can 
timestamp the pulse relative to a local counter. And since ntp is such a 
simple protocol, it should be pretty easy to write a appropriate ntp 
server routine that just hands out the time from GPS, including leap 
second indications.

Thoughts? Has it been done before, preferably with open source? I'd love 
to make it myself but I have to finish the GPSDO first :-)

-- m. tharp



------------------------------

Message: 5
Date: Sun, 19 Aug 2012 10:06:27 -0700
From: Chris Albertson <albertson.chris at gmail.com>
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Modern motherboard with RS232 port
Message-ID:
	<CABbxVHuv_HkjMNMELkPhUmYvtjFA11YbYe-Cn45tF6UEVpneFA at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

This sounds like a newer version of the board I use.   The thing to check
is if the CPU heat sink has a fan or not.  Having no fan indicates that the
CPU is not using much power.  It also removes a common failure point.

To reduce power even more.  On an NTP server you can unplug the keyboard,
mouse and monitor and if you have other servers on the LAN configure one as
a "boot server" and have it run TFTP then your NTP server does not need a
disk drive.  It can run off a "RAM disk".  This makes it very fast, even
faster than a SSD and it saves some cash.  Makes backup easy too as there
is nothing to backup if there is no local storage.  If you don't have a
TFTP server use a small notebook size disk drive. Even a 80GB drive is
overkill.  You can also boot from a USB thumb drive and run a RAM disk.

It is worth it to look at your electric bill to find how much you pay for
power.  Here I'm at $0.21 per KWH.  A full size PC server can use 250W or
more.  There are 8760 hours in a year so you get $460 per year to run that
250W PC.  The little Atom will pay for itself in just a few months.  The
first time I did that calculation, my "power hogs" where given away.




On Sun, Aug 19, 2012 at 7:42 AM, Stan, W1LE <stanw1le at verizon.net> wrote:

> Hello The Net,
>
> For your consideration:
>
> The INTEL model DN2800mt ITX mother board uses a ATOM CPU and
> draws about 11 watts of AC power when configured as:
> (I have not measured DC power yet.)
>
> 30 GB OCZ Nocti mSATA solid state drive,
> WIN7 pro, 64 bit, USB keyboard and mouse
> APEX MI-0008 case.
>
> Also has:
> parallel port available on mother board, you extend to a connector
> RS232 serial port available on mother board, you extend to a connector
> a single DC power supply from 11 to 19 V DC.
> 1 each PCIe expansion port, I will use with a premium 4 channel sound card
> SATA ports available for HDD/SDD,
> USB ports are available,
> Motherboard sound, and Gigalan.
>
> I have not played with NTP, (yet), but it sounds like a decent time nut
> technical challenge.
>
> My application is for a remote site with only 13V DC power available from
> PV/batteries.
> Then use fiber ethernet to get off site.
>
> The INTEL website would have further details.
>
> Stan, W1LE    Cape Cod   FN41sr
>
>
>
>
> ZZZZz
>
>
> ______________________________**_________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/**
>
mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/tim
e-nuts>
> and follow the instructions there.
>



-- 

Chris Albertson
Redondo Beach, California


------------------------------

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