[etherlab-users] etherlab dc sync check

[Jun Yuan]

Hi Graeme,

It is a great pleasure to hear from you. Your original patch helped me a
lot, as I once  suffered from the jitter of the master, too. And I sent a
Email to the mailing list
http://lists.etherlab.org/pipermail/etherlab-users/2013/002026.html,
pointing out another little problem in the original patch, which still
exits in the Etherlab master 1.5.2. I hope Florian would merge those
patches into the repository soon.

Thank you for supporting my thought that the master calculates an incorrect
initial time.

As Jereon pointed out, it's strange that the convergence time would depend
on the number of slaves. I feel the same. Although the master initialises
one slave at a time, the function ecrt_master_sync_slave_clocks() send
those sync datagrams all the time since the user loop starts. I think the
log from the master might make it look like that all the slave are synced
once at a time, but the sync process(drift compensation) is carried out for
all the slaves all the time in the background. Am I right?

Thanks again for all the help you offered.

Jun

On Sun, Jan 5, 2014 at 11:43 PM, Graeme Foot <Graeme.Foot at touchcut.com>wrote:

>
> Hi,
>
> It's a while ago now that I looked into it, but I originally had all sorts
> of problems with the dc clock system.  I could never get my yaskawa amps
> stable using the PC clock as the time master.  There is just way too much
> jitter.  Instead I wrote the original patch that selects a slave to use as
> the master time for both the rest of slaves and the PC master clock.
>
> As a side note, this is the default method used by TwinCAT.  They call the
> mode: "Master time/cycle updated to match ref slave time".
>
> This system in the Etherlab master 1.5.2 is currently broken.  I sent in a
> patch for it a while ago:
> http://lists.etherlab.org/pipermail/etherlab-users/2013/002162.html
>
>
> The second issue is the time it takes to sync a slave.  My memory is a bit
> rusty here and I never had time to fully investigate, but essentially the
> master often seems to calculate an incorrect initial time.  I think I got
> this down to consistently being within +-1ms which takes approx 3 seconds
> to sync (my RT cyctle time is 1ms).
>
> However, the more slaves you have, the longer it takes as the master
> initialises and syncs one slave at a time.
>
>
> I don't have much time in the next couple of months to help test, but I
> thought I would let you know about the patch above in case you were going
> to use the ref slave as the master time clock.
>
>
> Regards,
> Graeme.
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