[etherlab-users] etherlab dc sync check

[Jeroen Van den Keybus]

As far as 'simple experiment' goes. Here is the requested log of a 17-slave
configuration:


[2020582.839193] EtherCAT DEBUG 0-0: Checking system time offset.
[2020582.843201] EtherCAT DEBUG 0-0: DC 64 bit system time offset
calculation: system_time=1388788619730212737 (corrected with 4000000),
app_time=1388788619729210397, diff=-1002340
[2020582.843204] EtherCAT DEBUG 0-0: Setting time offset to
1388787098688224529 (was 1388787098689226869)
[2020582.847211] EtherCAT DEBUG 0-1: Checking system time offset.
[2020582.851219] EtherCAT DEBUG 0-1: DC 64 bit system time offset
calculation: system_time=1388788619738253673 (corrected with 4000000),
app_time=1388788619737210345, diff=-1043328
[2020582.851221] EtherCAT DEBUG 0-1: Setting time offset to
1388787098694672687 (was 1388787098695716015)
[2020582.855227] EtherCAT DEBUG 0-2: Checking system time offset.
[2020582.859235] EtherCAT DEBUG 0-2: DC 64 bit system time offset
calculation: system_time=1388788619746127955 (corrected with 4000000),
app_time=1388788619745210316, diff=-917639
[2020582.859237] EtherCAT DEBUG 0-2: Not touching time offset.
[2020582.863244] EtherCAT DEBUG 0-3: Checking system time offset.
[2020582.867251] EtherCAT DEBUG 0-3: DC 64 bit system time offset
calculation: system_time=1388788619754132695 (corrected with 4000000),
app_time=1388788619753210302, diff=-922393
[2020582.867253] EtherCAT DEBUG 0-3: Not touching time offset.
[2020582.871260] EtherCAT DEBUG 0-4: Checking system time offset.
[2020582.875267] EtherCAT DEBUG 0-4: DC 64 bit system time offset
calculation: system_time=1388788619762180961 (corrected with 4000000),
app_time=1388788619762210451, diff=29490
[2020582.875269] EtherCAT DEBUG 0-4: Not touching time offset.
[2020582.879278] EtherCAT DEBUG 0-5: Checking system time offset.
[2020582.883286] EtherCAT DEBUG 0-5: DC 64 bit system time offset
calculation: system_time=1388788619767191997 (corrected with 0),
app_time=1388788619770210343, diff=3018346
[2020582.883288] EtherCAT DEBUG 0-5: Setting time offset to
1388787098704211274 (was 1388787098701192928)
[2020582.887294] EtherCAT DEBUG 0-6: Checking system time offset.
[2020582.891302] EtherCAT DEBUG 0-6: DC 64 bit system time offset
calculation: system_time=1388788619775150970 (corrected with 0),
app_time=1388788619778210426, diff=3059456
[2020582.891304] EtherCAT DEBUG 0-6: Setting time offset to
1388787098700760295 (was 1388787098697700839)
[2020582.895311] EtherCAT DEBUG 0-7: Checking system time offset.
[2020582.899318] EtherCAT DEBUG 0-7: DC 64 bit system time offset
calculation: system_time=1388788619783154795 (corrected with 0),
app_time=1388788619786210495, diff=3055700
[2020582.899321] EtherCAT DEBUG 0-7: Setting time offset to
1388787098701077013 (was 1388787098698021313)
[2020582.903327] EtherCAT DEBUG 0-8: Checking system time offset.
[2020582.907334] EtherCAT DEBUG 0-8: DC 64 bit system time offset
calculation: system_time=1388788619791155722 (corrected with 0),
app_time=1388788619794210387, diff=3054665
[2020582.907337] EtherCAT DEBUG 0-8: Setting time offset to
1388787098702059792 (was 1388787098699005127)
[2020582.911343] EtherCAT DEBUG 0-9: Checking system time offset.
[2020582.915351] EtherCAT DEBUG 0-9: DC 64 bit system time offset
calculation: system_time=1388788619799144106 (corrected with 0),
app_time=1388788619802210392, diff=3066286
[2020582.915353] EtherCAT DEBUG 0-9: Setting time offset to
1388787098703046442 (was 1388787098699980156)
[2020582.919360] EtherCAT DEBUG 0-10: Checking system time offset.
[2020582.923367] EtherCAT DEBUG 0-10: DC 64 bit system time offset
calculation: system_time=1388788619807217599 (corrected with 0),
app_time=1388788619810210385, diff=2992786
[2020582.923369] EtherCAT DEBUG 0-10: Setting time offset to
1388787098694401972 (was 1388787098691409186)
[2020582.927376] EtherCAT DEBUG 0-11: Checking system time offset.
[2020582.931383] EtherCAT DEBUG 0-11: DC 64 bit system time offset
calculation: system_time=1388788619815217343 (corrected with 0),
app_time=1388788619818210352, diff=2993009
[2020582.931386] EtherCAT DEBUG 0-11: Setting time offset to
1388787098694270706 (was 1388787098691277697)
[2020582.935392] EtherCAT DEBUG 0-12: Checking system time offset.
[2020582.939400] EtherCAT DEBUG 0-12: DC 64 bit system time offset
calculation: system_time=1388788619823158753 (corrected with 0),
app_time=1388788619826210432, diff=3051679
[2020582.939402] EtherCAT DEBUG 0-12: Setting time offset to
1388787098702271332 (was 1388787098699219653)
[2020582.943409] EtherCAT DEBUG 0-13: Checking system time offset.
[2020582.947416] EtherCAT DEBUG 0-13: DC 64 bit system time offset
calculation: system_time=1388788619831157270 (corrected with 0),
app_time=1388788619834210362, diff=3053092
[2020582.947418] EtherCAT DEBUG 0-13: Setting time offset to
1388787098703045985 (was 1388787098699992893)
[2020582.951425] EtherCAT DEBUG 0-14: Checking system time offset.
[2020582.955432] EtherCAT DEBUG 0-14: DC 64 bit system time offset
calculation: system_time=1388788619839165891 (corrected with 0),
app_time=1388788619842210326, diff=3044435
[2020582.955435] EtherCAT DEBUG 0-14: Setting time offset to
1388787098703499171 (was 1388787098700454736)
[2020582.959441] EtherCAT DEBUG 0-15: Checking system time offset.
[2020582.963449] EtherCAT DEBUG 0-15: DC 64 bit system time offset
calculation: system_time=1388788619847182087 (corrected with 0),
app_time=1388788619850210371, diff=3028284
[2020582.963451] EtherCAT DEBUG 0-15: Setting time offset to
1388787098700973845 (was 1388787098697945561)
[2020582.967458] EtherCAT DEBUG 0-16: Checking system time offset.
[2020582.971465] EtherCAT DEBUG 0-16: DC 32 bit system time offset
calculation: system_time=1116891966 (corrected with 0),
app_time=1388788619858210417, diff=3048243
[2020582.971467] EtherCAT DEBUG 0-16: Setting time offset to 614131959 (was
611083716)

[2020583.075648] EtherCAT DEBUG 0-1: Checking for synchrony.
[2020583.079655] EtherCAT DEBUG 0-1: 37 ns difference after 4 ms.

Cycle time: 1ms


J.


2014/1/3 Jun Yuan <j.yuan at rtleaders.com>

> Oh, I understand, you're talking about synchronizing the master clock
> to the ref slave. This has been implemented in the etherlab master.
> You need to use the function ecrt_master_reference_clock_time()
> instead of ecrt_master_sync_reference_clock(). An example is given in
> example/rtai_rtdm_dc.
>
> Well, I think most of us are still used to sync reference clock to
> master. And yes, sync master to ref clock would make the situation a
> little bit better, as the ref clock itself doesn't need any adjustment
> any more, making the ref clock signal stable for the other slaves. But
> since the other slave are still having a bad time offset from the
> master to have a same timebase as the ref_clock, they still suffer
> from a large diff at the beginning of drift compensation. The problem
> is not still there.
>
> I need some volunteers to do a simple experiment for me. You'll just
> need a normal master application based on the current etherlabmaster
> and a ethercat bus network with at least one slave having DC enabled.
> 1. running your master application for about 10 minutes. This would be
> enough for all the DC sync on the bus get converged. So that all the
> DCs are running synchronized. You can check that with „ethercat
> reg_read -tsm32 0x92c“, it should  be something below 1000 ns.
> 2. turn the debug level of master to 1 using „sudo ethercat debug 1“.
> 3. stop the master application and restart it right away, while don't
> shut down your slaves. Your slaves should still have a relative good
> sync with each other.
> 4. check you system log, look for the lines like
>
> [ 9766.885265] EtherCAT DEBUG 0-0: DC 64 bit system time offset
> calculation: system_time=xxxxxxxx (corrected with xxxxxxxx),
> app_time=xxxxxxx, diff=xxxxxxxx
> [ 9766.885268] EtherCAT DEBUG 0-0: „Setting time offset to xxxxxxx
> (was xxxxxxx)“ OR: „Not touching time offset.“
> …
> [ 9767.292758] EtherCAT DEBUG 0-0: Checking for synchrony.
> [ 9767.296758] EtherCAT DEBUG 0-0: Sync after    4 ms:    xxxxxxx ns
>
> send these 4 lines of your system log to me, and tell me the cycle
> time of your loop. That’s it. Thanks!
>
> On Fri, Jan 3, 2014 at 10:52 AM, Slutsker, Rasty
> <rasty.slutsker at servotronix.com> wrote:
> > Master clock is accurate (more or less), but delivery is not, since
> software is involved.
> > I'm just asking why slave(s) shall synchronize to "jumpy" clock of
> master? Maybe be it would be more correct, if master could synchronize
> itself to the first slave and then will run pll adjusting it's clock to the
> slave's one?
> > In that case we can completely eliminate this time-consuming
> synchronization phase.
> >
> > Say,
> > a) master sends it's virtual clock to the first slave and that slave
> becomes a clock master
> > b) master re-distributes fist slave's clock to other slaves
> > c) master adjust it's clock permanently, relatively to the clock master
> (first slave)
> > d) master periodically re-distributes clock from the first slave to
> other in order to eliminate time skew in slave.
> >
> >
> > ________________________________________
> > From: Jun Yuan [j.yuan at rtleaders.com]
> > Sent: Friday, January 03, 2014 11:10 AM
> > To: Slutsker, Rasty
> > Cc: Jeroen Van den Keybus; Raz; etherlab-users at etherlab.org
> > Subject: Re: [etherlab-users] etherlab dc sync check
> >
> > I'm not saying that the clock of the master is inaccurate. I'm saying
> > that the master software does a bad job in the calculation of the time
> > offset for each slave. It should not use jiffies in the calculation,
> > It should not have any correction at all. The app_time when the fprd
> > datagram to 0x0910 is sent, let's call it app_time_sent, is exactly
> > the time which should be compared to the system time of the slave.
> >
> >> Why not just send once a current muster time to the first slave, then
> propagate(copy)  it to other slaves, and run PLL in the master that adjust
> itself to the fist slave (clock master)?
> >
> > I think we cannot do that, it's against the ethercat standard :)
> > It actually works similiar like you suggest, just in another way. It
> > is something like this:
> > Ref clock -> Master clock
> > 1. The master asks the first slave which time it has.
> > 2. The master compares the timestamp with its app time, and sends a
> > new time offset to the first slave.
> > 3. The first slave adds the new time offset to its clock. Now he has
> > the same time as the master. Drift is the next thing to worry about.
> >
> > Other slave clock -> Ref clock
> > 1. The master asks the slave which is not a ref clock which time it has.
> > 2. The master compares the timestamp with the time of the ref clock,
> > and sends a new time offset to the slave.
> > 3. The slave adds the new time offset to its clock. Now he shall have
> > the same time as the ref clock.
> >
> > I believe the current etherlabmaster doesn't do well in step 2. it
> > could be done better.
>
>
>
> --
> Jun Yuan
> [Aussprache: Djün Üän]
>
> Robotics Technology Leaders GmbH
> Am Loferfeld 58, D-81249 München
> Tel: +49 89 189 0465 24
> Mobile: +49 176 2176 5238
> Fax: +49 89 189 0465 11
> mailto: j.yuan at rtleaders.com
>
> Umlautregel in der chinesischen Lautschrift Pinyin: Nach den Anlauten
> y, j, q, und x wird u als ü ausgesprochen, z.B. yu => ü,  ju => dschü,
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>
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