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by Paul Kennedy
Tue Oct 16, 2012 12:38 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi, I am using the kernel you built ;-) I purchased the suregps direct from the manufacturer at: http://www.sureelectronics.net/goods.php?id=99 I was not aware the network stack has a 1 millisec limitation. Where did you come across that? Maybe NTP on the client PC is taking it into account via the ...
by Paul Kennedy
Mon Oct 15, 2012 3:43 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi Chris, Thanks for your plots. Mine can be found at http://secondthoughts.no-ip.org/ntp/index.php I rarely see my pi drift off more than a couple of microsecs, and I have pretty much followed your guide, so am interested why we see a difference. I am using the suregps which has a 3.3v pps so no ne...
by Paul Kennedy
Thu Oct 04, 2012 4:44 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

No problem. I suspect for most situations, millisecond timekeeping is sufficient. The nice thing about ntp is it will prevent your clock jumping about, and slew rather than step your clock. This is really useful for downstream apps which typically expect time to march forwards.
Pk
by Paul Kennedy
Wed Oct 03, 2012 4:55 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi, serial data is serial data. PPS is merely a low voltage pulse at regular intervals. On a regular PC, it is feasible to hook up a PPS pulse to the DCD handshake lines (typically pin1) of COM port, but a pi does not have a regular serial port, so the answer to your question is a clear no. And in r...
by Paul Kennedy
Tue Oct 02, 2012 4:39 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi Joe, it is not possible to get pps via USB (physically not possible - no wires), therefore you must use the pps 'test' pins on the sure card, and connect them to the GPIO. have a look at this plot. It shows my pi settling after a reboot (I had it off for the weekend) http://secondthoughts.no-ip.o...
by Paul Kennedy
Tue Sep 25, 2012 6:54 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hey Peter, My initial results of the kernel pps suggest microsecond level synchronisation. Do you believe hard pps will be even better? Can you outline the benefits of hardpps over kernel pps? Good call on the kernel compile process. I bashed away with in on a mac over the weekend, but gave up. Too ...
by Paul Kennedy
Tue Sep 25, 2012 1:48 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi Joew, I am no longer using the USB interface as it does not support pps. I made a custom cable for serial + PPS. My offset and jitter errors reduced from 1-5 millisecs to 1-5 microsecs. If a few millisecs is sufficient for you, then USB would be fine. It is certainly easier. Getting microsecs is ...
by Paul Kennedy
Mon Sep 24, 2012 3:59 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Joew,
Here is a link to my pi with the above gps. Hopefully the link is self explanatory and you can see for yourself what you would get.

http://secondthoughts.no-ip.org/
by Paul Kennedy
Sun Sep 23, 2012 1:43 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi joew, I am using a unit from sure: http://www.sureelectronics.net/goods.php?id=99 I chose it because it has a 3.3v output for both NMEA and PPS, which means I can make a direct connection to the pi, rather than a level shifter between. I am not completely 100% happy with the unit, but it seems to...
by Paul Kennedy
Tue Sep 18, 2012 1:57 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi, Peter, I started fooling around with github this evening. Looks pretty simple. https://github.com/secondthoughts I will push my code there in the near future. Just need to sort out a reliable flow between my pi<-->mac<-->github I am intrigued with your idea for the hardpps driver. Can you please...
by Paul Kennedy
Tue Sep 18, 2012 5:49 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi, Good idea to publish my web pages on github. I will certainly do this. I just need to complete the work on PPS then I will get back to the web pages sub-project. I really like your idea for hardpps. I think breaking it out into a kernel discipline away from the NMEA driver is the correct origina...
by Paul Kennedy
Tue Sep 18, 2012 2:33 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi, my apologies. I am using the GPS from SureElectronics. http://www.sureelectronics.net/goods.php?id=99 It is pretty easy to get up and running, but I am starting to find some limitations, specifically with the control of NMEA sentences. It looks like I cannot configure the sentences. All I need i...
by Paul Kennedy
Mon Sep 17, 2012 3:02 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Had a bit of a win today. I have been waiting for my gps from sure for almost a month. One turned up on Saturday - at last. Guess what, another one turned up Monday. I guess it must have self replicated while on the long boat from China. I will ask them if they would like me to send it back. I have ...
by Paul Kennedy
Mon Sep 17, 2012 12:03 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi Peter, your last post was rather confusing. I am not sure what you were attempting to state. My sure gps arrived on Saturday morning. The USB connectivity worked out of the box. I then wired up the serial RS232 and it also worked without trouble. I have contacted the manufacturers to see if I can...
by Paul Kennedy
Tue Sep 11, 2012 2:42 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

aquarat, I am busy tidying up some of my experimental code, and will provide it to yourself when I am happy with it. It has been running a couple of weeks without failure, but I have quite a few log files in place for monitoring purposes. You will need a web server (I use nginx) php (I use php-fpm)....
by Paul Kennedy
Mon Sep 10, 2012 3:23 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi Aquarat, Just got back from my work travels. I had another crack with this small dongle GPS (I received the manual form usglobalsat) and I managed to change bauds, remove superfluous sentences etc. So far the results are a significant improvement over my previous posts, but they are still at the ...
by Paul Kennedy
Fri Sep 07, 2012 8:52 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi travelling this week, but I believe I can improve this. My goal is 1 millisecond. The GPS manufacturer kindly provided the instruction set to manage output sentences and baud rates. I will be able to test my theory next week. Will also seek out a static IP. If this all works, I will have a very c...
by Paul Kennedy
Sat Sep 01, 2012 1:32 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

I have figured out what the issue is with this device. It runs at a very slow baud of 4800. While that is not a problem in itself, the device appears to be hardwired to output various NMEA sentences. The first one it outputs is $GPGSA (the satellites in view). Unfortunately, this sentence has a high...
by Paul Kennedy
Fri Aug 31, 2012 4:32 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi, One of the 2 gps units turned up tonight. unfortunately it was the USB dongle from globalsat... http://www.globalsat.co.uk/product_pages/gsat_products_cable_ND100S.htm 1. Plug it into the USB port in the pi. 2.make sure it works... stty -F /dev/ttyUSB0 ispeed 4800 && cat < /dev/ttyUSB0 $GPGLL,31...
by Paul Kennedy
Wed Aug 29, 2012 4:14 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Fair enough. Dont forget to post if you get it solved! Tonight, I made a small experimental page to plot the differences between the reference clocks with the aim of trying to better understand their relationships. I plot the offset, jitter and delays. I am hosting it on my pi at: http://secondthoug...
by Paul Kennedy
Wed Aug 29, 2012 11:23 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

hi, one more thing to try...
I note both NMEA and PPS appear as stratum0 devices. NTP may be getting confused as they are not co-incident, and both claim to be excellent. maybe set the nmea to a lower stratum, eg 2?

worth a quick try
by Paul Kennedy
Wed Aug 29, 2012 10:40 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hmm, To make more progress, I really need to get a gps hooked up to my pi, so right now there is not much more I can do. If my sure GPS works out of the box, we can then figure why you have trouble. Thanks for the feedback on the web page. I will tinker some more in the evenings, but it pretty much ...
by Paul Kennedy
Wed Aug 29, 2012 1:13 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

ok. thanks for the tip on the images. I will do likewise. A few things to try and nail this... 1. It looks like you have a server on your LAN at 10.0.0.8 I would make it update quicker so you can debug faster. I would dalos make it no select so we can focus on the NMEA + PPS (my guess is you will sh...
by Paul Kennedy
Tue Aug 28, 2012 12:55 pm
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi, yes, that is exactly what is happening. It is not sure who to believe right now. Scoping will remove an unknown form the dilemma.

good luck.
by Paul Kennedy
Tue Aug 28, 2012 11:06 am
Forum: Other projects
Topic: NTP PPS
Replies: 285
Views: 135222

Re: NTP PPS

Hi this is ok. We are now getting a better idea of the difference between the NMEA sentence and the PPS pulse. If there is a big difference, NTP will reject both refclocks (due to ambiguity). Therefore, you now need to figure out what the actual difference is. When they line up, NTP will be in a hap...

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