[etherlab-users] DC-Synchronization - Sync signal generation

[Jun Yuan]

Hi,

that's all right. I'm using Xenomai. I just want to demonstrate the idea
about how to synchronize the master clock to ref slave clock in an
alternative way. I choose the RTAI example to have the comparison with the
method of Graeme Foot.

You can test the rest nevertheless without that part. I didn't change the
API, so you don't need to change anything in your code. But
1) If you call ecrt_master_application_time() outside of the loop, it is
recommended that you remove it.
2) And only if you use ecrt_master_reference_clock_time(), you need to
notice that at the program start, before the calculation of dc system time
offsets for each slave has been done, ecrt_master_reference_clock_time()
would now have errno EAGAIN to notify the user that the ref clock is not
ready yet. So it is worth to always check the return value of
ecrt_master_reference_clock_time(), like I did in my rtai_rtdm_dc example.

That's it.

Regards,
Jun


On Fri, Apr 4, 2014 at 3:17 AM, Gavin Lambert <gavinl at compacsort.com> wrote:

> Hi Jun,
>
>
>
> Thanks; I’m having a look at it, but much of it is new to me.  I’m using
> PREEMPT_RT so my code is based on the dc_user example, not the RTAI
> examples, and I’d probably have to try adapting it before I could test it.
>
>
>
> Regards,
>
> Gavin Lambert
>
>
>
> *From:* Jun Yuan [mailto:j.yuan at rtleaders.com]
> *Sent:* Friday, 4 April 2014 01:46
> *To:* Gavin Lambert
> *Cc:* etherlab-users at etherlab.org
> *Subject:* Re: [etherlab-users] DC-Synchronization - Sync signal
> generation
>
>
>
> Hi Gavin,
>
> your interest is my motivation. I have attached the bundle file.
>
> My changes is base on the newest Version 1.5.2 in 'stable-1.5' branch. I
> added a new 'rtleaders' branch first and did all my changes on that. So
> after "$ hg unbundle etherlab_1.5.2_jyuan.hg", don't forget to switch to
> the 'rtleaders' branch using "$ hg update rtleaders".
>
> I found a better way of synchronizing the master clock to ref slave clock.
> It is much faster and more stable. I managed to port my C++ code into C
> code in the rtai_rtdm_dc example today, but I cannot test if the new code
> compiles right now. If you have a rtai environment, please test it for me
> if it compiles, and give me some feedback.
>
> Besides that, there is a more accurate DC time offset calculation. There
> should be no more errors like "Slave did not sync after 5000ms". The
> accurate time offset estimation saves much time for the DC Sync procedure.
> Slaves would have such a small dc diff (several hundred ns maybe) at the
> beginning of the dc sync check, that I even changed
> EC_SYSTEM_TIME_TOLERANCE_NS from 1000000ns to 1000ns.
>
> The postponed check of master->has_app_time makes the error "No app_time
> received up to now, but master already active" away.
>
> And there are the bugfix for ecrt_master_select_reference_clock() from
> Graeme Foot, and some other bug fixes from Jeroen Van den Keybus.
>
>
>
> Any feedback is welcome. Have fun testing those changes!
>
>
>
> Jun
>
>
>
> On Thu, Apr 3, 2014 at 12:13 AM, Gavin Lambert <gavinl at compacsort.com>
> wrote:
>
> On 2 April 2014 22:40, quoth Jun Yuan:
>
> > But there is a reason why we all put the ecrt_master_application_time()
> outside
> > the loop. Because we all got burned by the error "No app_time received
> up to
> > now, but master already active.", which is a timing bug in Etherlab. I've
> > resolved the problem by change the code of Etherlabmaster, which get rid
> of
> > the "No app_time" bug. Now I don't need to call
> ecrt_master_application_time()
> > outside the loop any more. I will publish the bundle to the mailing list
> when
> > I have time.
>
> I'd be very interested to see this.  Slave sync timing, "no app time", and
> the 5000ms sync timeout have been a recurring bugbear for me.
>



-- 
Jun Yuan
[Aussprache: Djün Üän]

Robotics Technology Leaders GmbH
Am Loferfeld 58, D-81249 München
Tel: +49 89 189 0465 24
Fax: +49 89 189 0465 11
mailto: j.yuan at rtleaders.com

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tschü,  xu => schü.
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