Re: Comparing phase of physically distant signals

From	Don Y <this@isnotme.com>
Newsgroups	comp.arch.embedded, comp.realtime
Subject	Re: Comparing phase of physically distant signals
Date	2013-08-06 01:47 -0700
Organization	Aioe.org NNTP Server
Message-ID	<ktqd7j$j3q$1@speranza.aioe.org> (permalink)
References	(1 earlier) <WTPLt.1755$3z5.266@fx35.am4> <ktp1ci$dsj$1@speranza.aioe.org> <jxWLt.346$Yd5.283@fx30.am4> <ktppcd$3vf$1@speranza.aioe.org> <7xmwovo10s.fsf@ruckus.brouhaha.com>

Cross-posted to 2 groups.

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Hi Paul,

On 8/5/2013 10:12 PM, Paul Rubin wrote:
> Don Y <this@isnotme.com> writes:
>> This happens at some "real" (physical) time as well as
>> some *local* (wrt A) time.
>
> Pop science tells us there is no such thing as '"real" (physical) time'.
> Whether A happens before B depends on the location of the observer.
>
> Instead of all this philosophizing, could you instead say what practical
> problem you are trying to solve?

It's not "philosophizing" -- it's a statement of an actual
(standardized) implementation.

The problem I am trying to solve is:

*verifying* that an EXISTING, WORKING IMPLEMENTATION that synchronizes
local clocks on physically (electrically) separated devices to BETTER
THAN MICROSECOND LEVEL tolerances is *still* achieving that level of
performance AFTER DEPLOYMENT... when the devices in question are no
longer *physically* close enough together to be conveniently "probed"
at the same time (as they are when examined on a test bench)

To state this, again, in a way that you can *physically* imagine:

I have two physical, tangible devices that consume power, generate
heat, occupy space, etc.  I have a wire from a digital output
(under processor control) on each device.  The software on each
device will pulse this output periodically (a duty that serves no
actual purpose in the operation of the device) when the local clock
maintained by the software on the device thinks it is "time X"
(X being an actual number).  The crystal oscillators powering
the two devices operate at different nominal frequencies.  The
two devices are interconnected by an ethernet (CAT5) cable
that is >100 ft long (but of uncalibrated length).

When I turn both devices on and wait a while (depends on how I
have the time constants for the capture loop set) and then
connect the two digital outputs to a two channel scope, the
difference in absolute time between the two pulses is O(<1us).
Regardless of how often a new value of X is inserted in the
algorithm (e.g., every second, 5 seconds, 4 hours, etc.).

If I lengthen the cable between the two devices and repeat the
experiment, the results do not change.  I.e., the devices
retain the same degree of synchronization.

Now, when I pick up those two devices and stretch the cable out
so the devices are *really* separated by that 100+ feet, I still
*know* the two pulses are being emitted at the "same" time
(within a microsecond of each other).  But, I can't *show*
that (or verify it!) because my scope probes aren't long enough
to reach both devices at the same time.

If the two devices are deployed at opposite ends of a football
stadium, I have no easy/inexpensive way of verifying that this
part of the devices' functionality is still operating correctly.
Or, of verifying its performance under challenges.

> Does it still involve lawn sprinklers?
> If not, then what does it involve?  Supplying this info will surely
> bring some helpful clarity.  Thanks.

*I* use it to synchronize (control the timing relationship between):
- audio emitted from different "speakers"
- audio from said speakers with video from a "display device"
- audio received from a microphone with video from a camera
- determining the location of a moving target within an arena
- partitioning of resources (in time) across the system

I.e., the same way you use the "system clock" in a single processor
system (if these I/O's were all attached to that *single* system)

I've already engaged in conversations with colleagues and clients
regarding uses to:
- control phased ultrasonic arrays (emit & detect)
- deploy audio in "stadium scale" venues
- geological probes (emit & detect)
- industrial (process) control systems

[When a "capable" processor, memory, ethernet MAC/PHY plus
application specific I/O's can be deployed for a few dollars,
a few square inches of board space and a few watts, the
idea of tackling big projects with *lots* of processors
is inevitable.  (i.e., if you had a tough time dealing with
the *illusion* of parallelism, your head's going to spin
when you have to deal with *true* parallelism!!)]

Of course, you could also use this as a "better NTP".  And, other
industries have numerous applications for the same technology
(which is why it has been *standardized* and vendors are offering
COMMERCIAL PRODUCTS that implement this mechanism).  Use your
favorite search engine to research "PTP" or "1588" or "1588v2"
for more varied applications.

Common application domains include:
- automation technology (gasp!)
- Motion Control (think servo controls)
- Process Control
- Robotics
- CIPsync (DeviceNet)
- PROFInet
- Ethernet Powerlink
- LXI (instrumentation)
- Energy distribution and monitoring (SmartGrid)
- Geoscience
- Telecom
- A/V (there's a formal standard that eludes me at the moment)
- Military (gasp!)

Having a common, shared, synchronized notion of "time" across
physically separate devices is a powerful mechanism!  It affords
the system designer with capabilities that wouldn't be practical
(or economical) otherwise!

Some folks have taken this to an even *finer* degree of precision.
For example, those silly folks at CERN use a (greatly) enhanced PTP
implementation ("White Rabbit") that delivers sub-NANOsecond
(i.e., 10-9 seconds lest you didn't catch that on first read)
synchronization over distances of KILOMETERS.  (and here *I* was
aiming to do sub-MICROseconds over a CITY BLOCK!  :-/  Lack of
ambition??)

Someone should lecture those CERN folks (academics??) as to the
RELATIVISTIC IMPLICATIONS of their hair-brained scheme.  Don't they
*know* it *CAN'T WORK*???  Gotta wonder what those crazy europeans
are *smoking* to come up with such a silly idea!!  Maybe they need
a theoretical physicist on their staff...

Likewise, tell the folks at Cisco, Juniper, etc. that this is
a fool's goal before their stockholders discover they've spent
all that NRE money developing REAL PRODUCTS that implement these
*impossible* PTP mechanisms!!  There's NO MARKET FOR THEM!!!
You *can't* synchronize time over a distance!!  (or, so I'm told)

(Really??!)

To play Tom's card:  find the references.  Read them.  UNDERSTAND
THEM.  *Then*, come back and point out the FLAWS in their
implementations!  (because you obviously are not convinced that
*I* have already done this!)  Unless you can point out why
1588 *can't* work or why White Rabbit is pure fantasy, you
won't be able to offer me any useful comment on the problem
I'm addressing (because I *see* 1588 working in front of my eyes
so regard comments that it "can't work" as in sharp contrast
with "reality")

Again, to be specific:  tell me how I can verify/measure the
time relationship between those two pulse outputs WHEN THEY ARE
ACTUALLY SEPARATED BY HUNDREDS OF FEET.

--don

Thread

Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 00:45 -0700
  Re: Comparing phase of physically distant signals Jan Panteltje <pNaonStpealmtje@yahoo.com> - 2013-08-03 07:51 +0000
  Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 09:58 +0100
    Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 13:21 +0300
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 12:16 +0100
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 11:56 -0700
        Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:17 +0100
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 13:41 -0700
            Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 22:46 +0100
              Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 14:57 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 23:09 +0100
    Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 13:58 +0300
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 12:30 +0100
    Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 16:08 +0300
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 14:22 +0100
        Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-03 16:38 +0300
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 10:46 -0700
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 10:40 -0700
        Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:04 +0100
        Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-04 15:55 +0200
          Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-04 19:42 +0300
            Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-04 21:08 +0200
              Re: Comparing phase of physically distant signals upsidedown@downunder.com - 2013-08-05 15:28 +0300
                Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-05 22:17 +0200
                Re: Comparing phase of physically distant signals Richard Damon <Richard@Damon-Family.org> - 2013-08-05 23:20 -0400
    Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 14:26 +0100
    Re: Comparing phase of physically distant signals George Neuner <gneuner2@comcast.net> - 2013-08-03 14:47 -0400
  Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 08:17 -0700
    Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:08 -0700
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:37 +0100
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:57 -0700
          Re: Comparing phase of physically distant signals Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-08-04 15:58 +0200
      Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 12:44 -0700
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 18:36 -0700
          Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-04 09:56 -0700
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-05 14:53 -0700
              Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-05 15:38 -0700
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 01:25 -0700
                Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-07 08:06 -0700
                Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-07 09:21 -0700
  Re: Comparing phase of physically distant signals josephkk <joseph_barrett@sbcglobal.net> - 2013-08-03 15:40 +0000
    Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 10:05 -0700
      Re: Comparing phase of physically distant signals John S <Sophi.2@invalid.org> - 2013-08-03 12:13 -0500
        Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 10:26 -0700
          Re: Comparing phase of physically distant signals John S <Sophi.2@invalid.org> - 2013-08-03 12:51 -0500
            Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 11:54 -0700
              Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-03 20:27 +0100
                Re: Comparing phase of physically distant signals George Neuner <gneuner2@comcast.net> - 2013-08-05 03:26 -0400
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-05 10:34 +0100
                Re: Comparing phase of physically distant signals Richard Damon <Richard@Damon-Family.org> - 2013-08-05 23:29 -0400
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 08:53 +0100
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:49 -0700
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:34 -0700
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 12:18 -0700
        Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 12:52 -0700
          Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 13:21 -0700
            Re: Comparing phase of physically distant signals Jeff Liebermann <jeffl@cruzio.com> - 2013-08-03 13:31 -0700
              Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-03 14:46 -0700
                Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 15:03 -0700
                Re: Comparing phase of physically distant signals Jeff Liebermann <jeffl@cruzio.com> - 2013-08-03 17:25 -0700
            Re: Comparing phase of physically distant signals Joerg <invalid@invalid.invalid> - 2013-08-03 14:50 -0700
    Re: Comparing phase of physically distant signals "Paul E. Bennett" <Paul_E.Bennett@topmail.co.uk> - 2013-08-04 11:06 +0100
      Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-04 12:19 -0700
  Re: Comparing phase of physically distant signals John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> - 2013-08-03 11:47 -0700
  Re: Comparing phase of physically distant signals Richard Damon <Richard@Damon-Family.org> - 2013-08-03 18:23 -0400
  Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-05 16:53 +0100
    Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-05 13:19 -0700
      Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 00:27 +0100
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-05 20:09 -0700
          Re: Comparing phase of physically distant signals Paul Rubin <no.email@nospam.invalid> - 2013-08-05 22:12 -0700
            Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 09:12 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 01:47 -0700
              Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 10:08 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:25 -0700
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:48 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 10:49 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 03:06 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 11:57 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 10:28 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 21:52 +0100
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 01:34 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-07 09:46 +0100
              Re: Comparing phase of physically distant signals Les Cargill <lcargill99@comcast.com> - 2013-08-06 07:22 -0500
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 10:42 -0700
                Re: Comparing phase of physically distant signals Les Cargill <lcargill99@comcast.com> - 2013-08-06 23:04 -0500
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 23:50 -0700
                Re: Comparing phase of physically distant signals Les Cargill <lcargill99@comcast.com> - 2013-08-07 13:05 -0500
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 18:22 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-08 09:35 +0100
              Re: Comparing phase of physically distant signals Paul Rubin <no.email@nospam.invalid> - 2013-08-06 22:18 -0700
                Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-07 03:09 -0700
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-07 12:39 +0100
                Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-07 13:18 +0100
          Re: Comparing phase of physically distant signals Tom Gardner <spamjunk@blueyonder.co.uk> - 2013-08-06 09:23 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:02 -0700
          Re: Comparing phase of physically distant signals "Paul E. Bennett" <Paul_E.Bennett@topmail.co.uk> - 2013-08-06 09:49 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-06 02:17 -0700
  Re: Comparing phase of physically distant signals Paul E Bennett <Paul_E.Bennett@topmail.co.uk> - 2013-08-16 21:07 +0100
    Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-16 14:50 -0700
      Re: Comparing phase of physically distant signals Paul E Bennett <Paul_E.Bennett@topmail.co.uk> - 2013-08-18 19:55 +0100
        Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-19 11:43 -0700
          Re: Comparing phase of physically distant signals Paul E Bennett <Paul_E.Bennett@topmail.co.uk> - 2013-08-20 21:43 +0100
            Re: Comparing phase of physically distant signals Don Y <this@isnotme.com> - 2013-08-20 14:49 -0700

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