Re: [ntp:questions] Using NTP to calibrate sound app
no-...@no-place.org wrote: small packets. A calibration run would consist of an initial NTP syncronization with an audio packet, followed by a period of some What you are describing here isn't, I think, the use of NTP, but the use of SNTP. You seem to be making a measurement, form the server, over a short amount of time. True NTP measures frequency and time and does so over time periods long compared with the network and scheduling jitter. number of minutes during which I will just count audio packets, followed by a final NTP synchronization with the last audio packet. By knowing the time difference over some number of audio packets I hope to calculate the actual audio clock frequency for that device. The way to do it with NTP is to discipline the main clock frequency, over many hours, and then measure the time relative ot the system clock. You may well find that you don't have to measure the sound generator frequency because it may use the same crystal as the main clock. Doing this simply, requires that you have some form of kernel discipline for the clock that is able to interpolate between ticks, allowing for the frequency correction. If you try and do SNTP measurements at the start and end of a sort period of tone, you will be very susceptible to network delay variations. Incidentally, given that all phone networks are digital these days, even your old method is susceptible to clock errors in the network, although I think most networks use atomic time. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using NTP to calibrate sound app
no-...@no-place.org no-...@no-place.org wrote: Now I am considering an alternate means of performing this calibration using NTP. The iPhone and Android devices deliver audio to my app in small packets. A calibration run would consist of an initial NTP syncronization with an audio packet, followed by a period of some number of minutes during which I will just count audio packets, followed by a final NTP synchronization with the last audio packet. By knowing the time difference over some number of audio packets I hope to calculate the actual audio clock frequency for that device. I think the average internet connection from a device like an iPhone has so much jitter that this approach will not work reasonably well. (try to ping to an internet server and see what kind of jitter you have, it usually is terrible over UMTS, WiFi etc) ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using NTP to calibrate sound app
Rob nom...@example.com wrote: I think the average internet connection from a device like an iPhone has so much jitter that this approach will not work reasonably well. (try to ping to an internet server and see what kind of jitter you have, it usually is terrible over UMTS, WiFi etc) iPhones do have a GPS though, and there do exist apps (at least for Android, supposedly also for the iPhone) that sync time to this GPS. /ralph ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using NTP to calibrate sound app
Ralph Aichinger ra...@pangea.at wrote: Rob nom...@example.com wrote: I think the average internet connection from a device like an iPhone has so much jitter that this approach will not work reasonably well. (try to ping to an internet server and see what kind of jitter you have, it usually is terrible over UMTS, WiFi etc) iPhones do have a GPS though, and there do exist apps (at least for Android, supposedly also for the iPhone) that sync time to this GPS. I have no knowledge of the internal architecture of the iphone, but when this GPS receiver is internally connected using an emulated serial link that transfers NMEA packets, the accuracy of that time sync also will leave a lot to be desired. Fine for wristwatch time, not so good for measurements and calibrations. For that you need PPS information, which is usually not provided in designs not especially made for timekeeping. When you want accurate measurements, you need to run an ntpd process on the machine that continually averages the information from the GPS and disciplines the local clock using a slow loop, and then perform the measurement relative to this disciplined local clock. That way you avoid the jitter of individual GPS time readings. That said, I find it hard to believe that the same measurement cannot be done relative to the standard iphone local clock with enough accuracy for the original poster. Clocks tend to run quite accurately when compared to the precision required for typical audio applications. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using NTP to calibrate sound app
Maarten Wiltink maar...@kittensandcats.net wrote: Which is exactly why hardcoding pool.ntp.org _is_ allowable, in my opinion - and in fact indicated in such a case as this. In my opinion, it's not. Please read http://www.pool.ntp.org/en/vendors.html . -- Maurice ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using NTP to calibrate sound app
unruh un...@invalid.ca wrote in message news:tiLMs.55319$on7.49...@newsfe16.iad... On 2013-01-26, no-...@no-place.org no-...@no-place.org wrote: [...] I obviously don't want to hard-code for a specific time server because things could change after the user gets my app and it is unfair to send a whole block of users to the same server. The Server Pool looks promising. Does pool.ntp.org just behave like a Stratum 2 server so I could hard-code that URL into my implementation of NTP in my app? ... [...] And no you definitely should not hard code a site, unless it is one controlled by you. [...] Note pool.ntp.org does NOT have an IP-- each dns request gives a different IP, so you need the name, not an IP. Which is exactly why hardcoding pool.ntp.org _is_ allowable, in my opinion - and in fact indicated in such a case as this. Exactly because (as I suspect you meant) it is not a fixed site, but a symbolic name that translates to some reasonable site that is available now. Incidentally, to the OP, it's not a URL. It is a DNS name. Groetjes, Maarten Wiltink ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] p351 fails to build on MSVC++2008EE
Steve, I see from the web page that Autogen is maintained by Bruce Korb. Bruce is well aware of the current issues in building NTP with MSVC++2008/2010EE, so patients is the key word here I guess. Thanks for the information. Regards, Ed On 2013-01-25, Mischanko, Edward T edward.mischa...@arcelormittal.com wrote: Who updates autogen and when is it expected? The AutoGen home-page is: http://www.gnu.org/software/autogen/ -- Steve Kostecke koste...@ntp.org NTP Public Services Project - http://support.ntp.org/ ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Updating the leapseconds file -- how to signal ntpd
I know of no way for NTP to know about the new file without restarting NTP itself. The drift file will allow it to come back into sync very quickly, so the consequences of a restart should be minimal. NTP reads the leapseconds file on start-up, I believe. Regards, Ed I'm using my configuration-management system to distribute a leapseconds file for ntpd. After the system installs the new file, what does it need to do for ntpd to recognize that the file has changed? (It is obviously undesirable to simply restart a stratum-1 ntpd; I'm looking for the mechanism that ntpd expects managers to use, if there is any.) -GAWollman -- Garrett A. Wollman| What intellectual phenomenon can be older, or more oft woll...@bimajority.org| repeated, than the story of a large research program Opinions not shared by| that impaled itself upon a false central assumption my employers. | accepted by all practitioners? - S.J. Gould, 1993 ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using NTP to calibrate sound app
In article 51033f49.215309...@news.eternal-september.org, no-...@no-place.org wrote: I am an app developer who has a precision audio frequency app for iPhone and Android devices. For my app the nominal crystal oscillator accuracy in these devices is not sufficient. Up until now I have been providing frequency calibration in my app by instructing the user to call the telephone feed of WWV (NIST) audio (using a separate landline phone) and let my app listen to the 500 Hz and 600 Hz tones. By analyzing the audio I can correct for the device's audio system clock deviation. Normally they only need to do this once after the app is installed because the stability of these devices is OK once I memorize the offset. Now I am considering an alternate means of performing this calibration using NTP. The iPhone and Android devices deliver audio to my app in small packets. A calibration run would consist of an initial NTP syncronization with an audio packet, followed by a period of some number of minutes during which I will just count audio packets, followed by a final NTP synchronization with the last audio packet. By knowing the time difference over some number of audio packets I hope to calculate the actual audio clock frequency for that device. My question is about the NTP procedure I should follow to do this. I obviously don't want to hard-code for a specific time server because things could change after the user gets my app and it is unfair to send a whole block of users to the same server. The Server Pool looks promising. Does pool.ntp.org just behave like a Stratum 2 server so I could hard-code that URL into my implementation of NTP in my app? I would appreciate any observations on the promise of this approach. How accurately do you need to calibrate? What will people use this app for? And how long can this calibration take before users revolt? Joe Gwinn ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using NTP to calibrate sound app
On 2013-01-26, David Woolley david@ex.djwhome.demon.invalid wrote: no-...@no-place.org wrote: small packets. A calibration run would consist of an initial NTP syncronization with an audio packet, followed by a period of some What you are describing here isn't, I think, the use of NTP, but the use of SNTP. You seem to be making a measurement, form the server, over a short amount of time. True NTP measures frequency and time and does so over time periods long compared with the network and scheduling jitter. number of minutes during which I will just count audio packets, followed by a final NTP synchronization with the last audio packet. By knowing the time difference over some number of audio packets I hope to calculate the actual audio clock frequency for that device. The way to do it with NTP is to discipline the main clock frequency, over many hours, and then measure the time relative ot the system clock. You may well find that you don't have to measure the sound generator frequency because it may use the same crystal as the main clock. Unfortunately ntpd does NOT change the crystal. It changes the way that software interprets the output of that crystal (eg do 1 vibrations equal a second or do 1002 vibrations?) The sound cards are almost certainly hard wired into the crystal, not software. Ie, the sound system does not, I believe, read the system clock in order to time the sound output. Doing this simply, requires that you have some form of kernel discipline for the clock that is able to interpolate between ticks, allowing for the frequency correction. If you try and do SNTP measurements at the start and end of a sort period of tone, you will be very susceptible to network delay variations. That will have to be within his error budget. Thus if the network jitter is 1ms, then he would have to measure for 44 sec to get down to one cycle per 44000 error (ie +- 1Hz for a 44100 sound ) Incidentally, given that all phone networks are digital these days, even your old method is susceptible to clock errors in the network, although I think most networks use atomic time. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
[ntp:questions] When is the kernel-mode time-stamping used under Windows? Must one add the type 22 driver line?
Folks, I've tried to follow this in the code, but it's beyond me, I'm afraid! Given: 1 - the modified serialpps.sys device driver is installed 2 - the support DLL is present 3 - the environment variable points to the support DLL is it necessary to add the ATOM driver to the ntp.conf file? I.e. do you /need/ a line such as: server 127.127.22.1 minpoll 4 to ensure that the kernel-mode driver is used? My testing on one Windows-8/64 system suggest that the driver is used whether or not a type 22 driver is specified, given the conditions above. I'm not complaining about this, just wondering whether anyone may be able to confirm that from the source code. The question arose because adding the line made no improvement to the jitter, which initially made me think that the driver was not being used, but further tests suggest it's the opposite - that the driver is being used whether you asked for it explicitly or not. Of course, given (1)..(3) above does rather suggest you want the kernel-mode, so the behaviour makes sense, even if it is a little confusing. [Yes, FreeBSD and Linux behave differently.] -- Thanks, David Web: http://www.satsignal.eu ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Using NTP to calibrate sound app
unruh wrote: On 2013-01-26, David Woolley david@ex.djwhome.demon.invalid wrote: You may well find that you don't have to measure the sound generator frequency because it may use the same crystal as the main clock. Unfortunately ntpd does NOT change the crystal. It changes the way that software interprets the output of that crystal (eg do 1 vibrations equal a second or do 1002 vibrations?) I was assuming that, if they shared a common crystal, one would simply read the ntpd frequency correction to get the frequency correction for the audio. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Updating the leapseconds file -- how to signal ntpd
In article n7sdnfngn4pywp7mnz2dnuvz_smdn...@megapath.net, Hal Murray hal-use...@ip-64-139-1-69.sjc.megapath.net wrote: I suggest submitting a feature request at https://support.ntp.org/bugs/index.cgi with a link back to the above bug since it will be the same area of code. Too many hoops to jump through. Maybe someone who already has an account at that site can do it. -GAWollman -- Garrett A. Wollman| What intellectual phenomenon can be older, or more oft woll...@bimajority.org| repeated, than the story of a large research program Opinions not shared by| that impaled itself upon a false central assumption my employers. | accepted by all practitioners? - S.J. Gould, 1993 ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] Updating the leapseconds file -- how to signal ntpd
2013/1/27, Garrett Wollman woll...@bimajority.org: In article CABrG=ZyT9ttE4Mea3yauWPru0euQ8TV4m7KHm0bHSwiYa=+b...@mail.gmail.com, Michael Tatarinov kuk...@gmail.com wrote: I know only one way. ntpq -c 'config: leapfile LEAPFILE That was what I was looking for! In my version of ntpq, at least, it's spelled ':config' rather than 'config:', but that did it. Unfortunately, this still doesn't get me anywhere, because the passwd command in ntpq 4.2.6 doesn't take any arguments. Looks like this is fixed in ntp-dev 4.2.7, so I'll have to wait until 4.2.7 becomes the official stable version. you can try to use ntpq 4.2.7 with ntpd 4.2.6 ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
