Keeping 'order' without RTC.

Engineers only speak to organ grinders not monkeys

YOU CANNOT ACHIEVE WHAT YOU WANT WITH WHAT YOU HAVE. Either follow the advise you are given (spent tuppence ha'penny on an RTC module) or take your business elsewhere.

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Cheer Up!  Things are getting worse at a slower rate.

Noted, but as the NMEA sentence (GPRMC if I remember correctly) is sent once a second, would the start of that sentence be sufficiently jitter- free to use as a PPS substitute? I'm asking for my own future reference.

My example has the serial interface. The only testing I did with it was to watch its output with a computer, as I was more interested in using it for navigation, driving XCSoar on an iPAQ 3630, than as a time source.

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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
org       |

Good enough to get wristwatch time. When you want the time to be correct within 100ms then it is not sufficient. There tends to be a lot of unpredictability in NMEA timing. Often you can alternatively select a manufacturer-specific protocol that performs better. But to get anywhere near the capabilities of GPS you really need a PPS signal fed to an input line that can issue interrupts. Traditionally a like like RS232 DCD is often used, but it requires a UART-interfaced RS232 port to perform well. In a Pi, a suitable GPIO input can be used. With PPS a fast system can be synchronized to well within 1us, for the Raspberry Pi it will be more like 10us.

Perhaps you might provide a link, Bill, so that I could update my Web page to help others....

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Cheers, 
David 
Web: http://www.satsignal.eu

On 05/03/2015 10:20, Martin Gregorie wrote: []

You may find that an internet source, even over Wi-Fi, provides better sync than the NMEA output of many GPS devices. It's often the last thing the internal processor generates and hence the most variable in its exact timing.

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Cheers, 
David 
Web: http://www.satsignal.eu

On 05/03/2015 10:51, Rob wrote: []

You can see how well, or otherwise, some PPS-synced Raspberry Pi cards are doing here:

Two caveats:

- all the RPi cards were updated to NTP 4.3.4 a few hours back which will have given rise to transients.

- one or two systems (e.g. RPi #6) are sitting on the bench, and getting sunlight directly towards them. This does no good at all for the temperature and hence timing stability!

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Cheers, 
David 
Web: http://www.satsignal.eu

Another light bulb goes on. Hallelujah!

I don't see how this is different from my claim.

I was not contesting your claim, simply presenting data which I had gathered here. I did say: "how well or otherwise". It does demonstrate though that in a more temperature controlled environment a Raspberry Pi (Raspberry Pi #1) can do better than an Intel Atom system (PC Pixie) in a heated room, and perhaps have a lower offset than your 10 microsecond figure.

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Cheers, 
David 
Web: http://www.satsignal.eu

Depeds on what you want. If you are happy with 10s of ms jitter, it is fine, If not, it is not fine. The nmea sentences are basically sent when the system has nothing better to do (like calculate a fix).

For watching it is pleanty accurate enough.

right now gives a link to their gps modules. Of course this is canada ebay. I just searched for "sure ebay store" and then typed in "gps" into the search box.

Thanks, Bill. Web page updated:

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Cheers, 
David 
Web: http://www.satsignal.eu

Interestingly, 2 of the major 20th century technologies were 'developed' by US collaborating: aviation & computing. USEnet originated as a collaborating device. But, apparently most USEnet users are now a generation younger than me and also stressed by the arrival of Toffler's 3-rd-wave economy.

Considering that many retirees are genetically programmed to play golf, imagine their reaction if you advised them to buy-a-ding-dong to get the ball in the hole.

So, back to the algorithm: the mathematical concept 'order' [as emphasised in the "Subject:"] is key. When Newton was called away from his desk of paper-work, he needed the papers to be 'stacked' in the same ORDER when he returned. Even if the cleaning-lady, had 'been there' during his absence, and , provided the 'order' was maintained, the real-time attributes were not needed.

So how can you achieve that by *thinking*, instead of buying a ding-dong that will put-the-ball-in-the-hole-for you.

Numerous suggestions have been made. He has not responded. If you are the OP, take one of the suggestions and impliment it. And not all required a "dingdong" (and an $8 dingdong is cheaper than the time he has already wasted)

>

One option, forget the idea of timestamps entirely. Name the files with sequential numbers. Be sure to zero pad so ls works as expected. You could even do the Basic programming trick of skipping numbers (e.g. by

10s) so you could insert items higher in the queue without renumbering. 000000010-playme.mp3 000000020-thesis.mp3 000000030-soothing.mp3 000000040-jamz.mp3

uh-oh, breaking news, add

000000000-sungoingnova.mp3

That is one of the "Chris Glur" troll morphs, so he is the OP. This is one of his trolling tactics: ignoring all advice and re-posting another poorly reworded phrasing of his original poorly worded question, with the implication that somehow none of the answers provided were "good enough" for him, because he's somehow smarter than everyone else yet completely unable to solve his own problem.

He only really cares about wasting our time, not his.

--keith

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kkeller-usenet@wombat.san-francisco.ca.us 
(try just my userid to email me) 
AOLSFAQ=http://www.therockgarden.ca/aolsfaq.txt 
see X- headers for PGP signature information

Which bit of DON'T FEED THE TROLL do you not understand?

That's the kind if original good idea which we need !! With the 'thread overflow' I nearly missed this 1 month old post. I'll try to implement your idea, when I've cleared the chaos.

Thanks.

And the Raspberry Pi can't run without a Real Time Clock.

You wasted all this time because you pretended to no know that.

Linux needs to be interrupted to actually work, so keeping time is intrinsic to the operating system.

Like I said way back when, all you have to do is set the time and date when you start the Pi up, something that used to be quite common. A hardware clock is only used to set the time when the computer starts, saving you a few keystrokes, the Pi or any Linux computer doesn't get time from the hardware clock other times (unless someone is configuring it differently, and a common thing then is to access a cesium standard on the internet, which would be another way do to this if the Pi is networked).

You waste everyone's time, and now thing some roundabout method is "good", when it is all about you being too lazy to set the time when you turn on the computer.

Michael