Re: [time-nuts] Posting style Was: looking for good description/generalized model for time adjustments
James, Your email posting style makes it very difficult to follow threads where you have posted replies. Most mail reader programs follow the convention, that on a reply, they automatically start with a header that identifies the last poster (In reply to message from xxx) and then quote the entire replied-to message by prefixing each line with a chevron in the first column. If another person replies later the same process is usually used, so when reading the latest message in the thread, one can determine the sequence of replies, because the oldest has maximum chevrons preceeding the lines, and the most recent comments have none. One can usually trace up the message to find the in response to-type headers and figure out who said what. Here's a link with a discussion of these conventions: http://en.wikipedia.org/wiki/Posting_style You seem to use a simple text method in your replies that doesn't add the chevron in front of the earlier stuff so your new reply and the last poster look to be at the same current sequence level. What's more, you often preceed your new reply lines with some random number of chevrons, making it appear in most mail reader programs that this new portion ought to be some much earlier part of the discussion. It also makes it a difficult detective process to figure out who said what in that message and any that follow. I don't want to start a big netiqette discussion, and you certainly have the right to do as you choose, but I would ask, that at minimum, you don't put chevrons in front of your new reply lines when you respond to previous messages. -Rex Lux, James P (337C) wrote: -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray Sent: Wednesday, July 29, 2009 2:51 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] looking for good description/generalized model for time adjustments Precisely so. And NTP may actually be the best model here. Does NTP's corrected output meet the must be monotonic and not discontinuous criteria (being too lazy to just go read the NTP docs, which I have, and which I'll take a look at after lunch). There is a lot of info available about ntp, you may have troubles finding what you want, especially if you don't already know what you are looking for. I'm being sloppy when I say ntp. It's both a protocol spec (RFC-whatever) and a reference implementation (ntpd) that is widely deployed. snip about ntp What OS are you using? FreeBSD is very good. Linux is not--so-good. RTEMS and/or VxWorks (I'm using RTEMS, others with whom we communicate use a variety of other things. And we don't have network connections per se.. That's why I'm looking for more generic descriptions that aren't tied to things like packet definitions or peculiarities of IP routing. Basically, all of these things should be able to be boiled down to two things: a synchronization signal and a synchronization message. The other mode is using a refclock. ntpd includes support of over 20 different types of clocks, many are no longer interesting. The key to getting good time is something like a PPS pulse and kernel support to grab a timestamp in the interrupt routing. There is also a batch of PLL code in the kernel that I don't understand. and it is that PLL code that is particularly interesting (Poul-Henning has useful information in kern/time_tc.c, etc.) For network traffic, ntp assumes the delays are symmetric. snip In my application, we don't need to probe the network to figure out the latencies. We know them apriori, and they are also very small compared to the required time precision. The part I'm interested in is the automated reconciliation of the always varying clocks/oscillators on the platforms, essentially trying to predict a bad clock with a good one. --- But it *is* the master, by fiat. Here's a scenario: A schedule is published that says: (MT = Master's time) At 12:00.001MT Box A puts out a pulse At 12:00.002MT Box B puts out a pulse At 12:01.001MT Box A puts out a pulse. Box A and Box B MUST follow Master Time, no matter how crummy it is. ntp is trying for UTC, the one great time. But that comes from outside ntp. You can simplify things a lot if you tell it (config file) to only use one server. For example, you could setup box A as the master and tell B to sync to it. It may be better to setup another box in a stable environment and sync both A and B to it. That gives B a stable target. -- Can't do that in this environment. The master is the master, and all the slaves are fore-ordained and must follow it as best they can. What I need to do, really, is figure out what best they can is. A Single board computer with non TCXO clock (on order of 10ppm variability over short term) is the
Re: [time-nuts] Posting style Was: looking for good description/generalized model for time adjustments
Yes.. I know.. We just changed institutional mail servers (now Exchange..) and then mail clients (now Outlook 2007..) I haven't figured out how to get the mail client to properly quote non-html messages. (I've got a call into the help desk as I write this..) Jim -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Sent: Wednesday, July 29, 2009 4:18 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Posting style Was: looking for good description/generalized model for time adjustments James, Your email posting style makes it very difficult to follow threads where you have posted replies. Most mail reader programs follow the convention, that on a reply, they automatically start with a header that identifies the last poster (In reply to message from xxx) and then quote the entire replied-to message by prefixing each line with a chevron in the first column. If another person replies later the same process is usually used, so when reading the latest message in the thread, one can determine the sequence of replies, because the oldest has maximum chevrons preceeding the lines, and the most recent comments have none. One can usually trace up the message to find the in response to-type headers and figure out who said what. Here's a link with a discussion of these conventions: http://en.wikipedia.org/wiki/Posting_style You seem to use a simple text method in your replies that doesn't add the chevron in front of the earlier stuff so your new reply and the last poster look to be at the same current sequence level. What's more, you often preceed your new reply lines with some random number of chevrons, making it appear in most mail reader programs that this new portion ought to be some much earlier part of the discussion. It also makes it a difficult detective process to figure out who said what in that message and any that follow. I don't want to start a big netiqette discussion, and you certainly have the right to do as you choose, but I would ask, that at minimum, you don't put chevrons in front of your new reply lines when you respond to previous messages. -Rex Lux, James P (337C) wrote: -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray Sent: Wednesday, July 29, 2009 2:51 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] looking for good description/generalized model for time adjustments Precisely so. And NTP may actually be the best model here. Does NTP's corrected output meet the must be monotonic and not discontinuous criteria (being too lazy to just go read the NTP docs, which I have, and which I'll take a look at after lunch). There is a lot of info available about ntp, you may have troubles finding what you want, especially if you don't already know what you are looking for. I'm being sloppy when I say ntp. It's both a protocol spec (RFC-whatever) and a reference implementation (ntpd) that is widely deployed. snip about ntp What OS are you using? FreeBSD is very good. Linux is not--so-good. RTEMS and/or VxWorks (I'm using RTEMS, others with whom we communicate use a variety of other things. And we don't have network connections per se.. That's why I'm looking for more generic descriptions that aren't tied to things like packet definitions or peculiarities of IP routing. Basically, all of these things should be able to be boiled down to two things: a synchronization signal and a synchronization message. The other mode is using a refclock. ntpd includes support of over 20 different types of clocks, many are no longer interesting. The key to getting good time is something like a PPS pulse and kernel support to grab a timestamp in the interrupt routing. There is also a batch of PLL code in the kernel that I don't understand. and it is that PLL code that is particularly interesting (Poul-Henning has useful information in kern/time_tc.c, etc.) For network traffic, ntp assumes the delays are symmetric. snip In my application, we don't need to probe the network to figure out the latencies. We know them apriori, and they are also very small compared to the required time precision. The part I'm interested in is the automated reconciliation of the always varying clocks/oscillators on the platforms, essentially trying to predict a bad clock with a good one. --- But it *is* the master, by fiat. Here's a scenario: A schedule is published that says: (MT = Master's time) At 12:00.001MT Box A puts out a pulse At 12:00.002MT Box B puts out a pulse At 12:01.001MT Box A puts out a pulse. Box A and Box B MUST follow Master Time, no matter how crummy it is. ntp is trying for UTC, the one great time. But that comes from outside ntp. You can
Re: [time-nuts] Posting style Was: looking for good description/generalized model for time adjustments
Test of quoting of responses.. This looks better, at least from here.. James Lux, P.E. Task Manager, SOMD Software Defined Radios Flight Communications Systems Section Jet Propulsion Laboratory 4800 Oak Grove Drive, Mail Stop 161-213 Pasadena, CA, 91109 +1(818)354-2075 phone +1(818)393-6875 fax -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Sent: Wednesday, July 29, 2009 4:18 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Posting style Was: looking for good description/generalized model for time adjustments James, Your email posting style makes it very difficult to follow threads where you have posted replies. Most mail reader programs follow the convention, that on a reply, they automatically start with a header that identifies the last poster (In reply to message from xxx) and then quote the entire replied-to message by prefixing each line with a chevron in the first column. If another person replies later the same process is usually used, so when reading the latest message in the thread, one can determine the sequence of replies, because the oldest has maximum chevrons preceeding the lines, and the most recent comments have none. One can usually trace up the message to find the in response to-type headers and figure out who said what. And here's a response.. Seems to have quoted properly. (of course, some centrally managed configuration update pushed out tonight might set it back...arghh) Jim ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Posting style Was: looking for good description/generalized model for time adjustments
Arrgh! Mike S wrote: At 07:17 PM 7/29/2009, Rex wrote... Your email posting style makes it very difficult to follow threads where you have posted replies. At least he's not top-posting. I did say this: I don't want to start a big netiqette discussion... Top/bottom is exactly the discussion I was thinking might happen. (Notice, I did both this time.) I'm happy with both. Sorry I sparked it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
