[etherlab-users] FW: Distributed Clock with Yaskawa SGDV drives

[Graeme Foot]

Hi,

Right, I see what you mean.

I hadn't sorted out my timing issues back then so it is more like due to that.  I've almost finished what I'm currently working on so I'll revisit it and get back to you.  


Graeme.



-----Original Message-----
From: Florian Pose [mailto:fp at igh-essen.com] 
Sent: Monday, 12 March 2012 22:08
To: Graeme Foot
Cc: etherlab-users at etherlab.org
Subject: Re: [etherlab-users] FW: Distributed Clock with Yaskawa SGDV drives

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Am 12.03.2012 00:03, schrieb Graeme Foot:
> Hi,
> 
> The slaves are not in OP before ecrt_master_activate().  They are
> in OP after ecrt_master_activate(), but before the first PDO
> datagrams were sent.

But this is what the application is responsible for. After activating
the master, the ecrt_master_send()/receive() methods have to be called
by the application, otherwise *no* bus communication (including slave
configuration) will take place. That's why I'm not understanding, why
slaves can go to OP before 'seeing' the fist process data...

> I was sorting out a few problems I was having at the time, so it's 
> probably not such an issue anymore.  However the main issue is that
> I'm running from a user space thread in RTAI.
> 
> What I originally had was:
> 
> ecrt_master_activate() ... setting up app objects to use pdo data
> etc ... rt_make_hard_real_time() rt_task_make_periodic(...,
> firstScanTime, ...) rt_task_wait_period() while (true) { ...
> ethercat polling stuff etc ... rt_task_wait_period() }
> 
> I needed to call ecrt_master_activate() (and then set up objects 
> referring to the pdo data) before making the thread hard realtime.
> In the time it took for the first hard period to start some of the
> slaves had already reached OP mode and missed a couple of PDO
> datagrams.

See above, after ecrt_master_activate() is called, there is no bus
configuration until you call ecrt_master_send() cyclically.

> So instead of that, I added an ethercat function to allow
> pre-assigning of the pdo data from user space so that the pdo data
> objects could be set up before calling ecrt_master_activate().  I'm
> also putting the ecrt_master_activate() call in a non-hard realtime
> helper thread so there is minimal time between the
> ecrt_master_activate() call and the PDO packets starting to be
> sent.
> 
> It all comes down to ecrt_master_activate() not being able to be
> called from a hard realtime thread in RTAI because it drops the
> thread out of hard realtime.

Sure, because memory has to be allocated. It never was never meant to
be called in real-time.

So before futher discussions I would like to have an explanation, why
the slaves are configured before the application calls ecrt_master_send().

Could you tell me the exact code revision including all patches you use?

- -- 
Viele Grüße,
Florian
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