Re: [RTnet-users] RTnet in combination with non-Linux/non-RTnet remote station

Wed, 10 Nov 2010 11:03:05 -0800

Am 10.11.2010 18:51, schrieb Anders Blomdell: 
On 2010-11-10 18.23, Vinzenz Bargsten wrote:
  
Hi,

can someone provide (more) information on how to run a RTnet
in combination with in this case one non-Linux/non-RTnet, i.e. windows machines?

The windows machine (robot controller), which runs some proprietary real-time 
software,
sends a UDP packet with XML strings every 12ms to the Linux machine.
The Linux machine receives and processes the data (<1ms) and has to answer in 
less than 12 ms.

At the moment,the setup on the Linux machine is:
kernel 2.6.32-7 x86_64 with xenomai 2.5.1, RTL8139 NIC
The data processing is done in/via OROCOS in a real time task.
There is no other machine on this network.

However, the problem is that the real time requirement is not met,
i.e. the answer from the linux machine sometimes takes more than 12ms.
Using wireshark we found out, that normally the answer is sent after (packet 
receive time) + ~0.5ms,
but after some time (minute(s)), it takes >40ms and several/the missing packets 
are sent at once.
    
Could it be that you are running a SMP machine? Then this might be of interest:

https://mail.gna.org/public/xenomai-core/2010-11/msg00053.html

later kernel, but the bug might exist in earlier versions (Jan can you comment
on this)?


to clarify it:
I don't use RTnet yet, i.e. the interface uses the normal kernel module and I want to use RTnet because these problems occur.
I am just not sure how to use RTnet with non-RTnet/tdma remote machines.
Indeed the Linux machine has a multi-core cpu, I can check further kernel infos tomorrow.

Regards
Vinzenz



  

    
This is a big problem, as the packets, which are sent from the Linux machine 
contain position data,
which should be commanded to a robot.
If the packets are delayed, the robot will stop/hold its position for this time,
which results in an non-smooth/impulsive movement, making the measurement useless.

So, what is the correct procedure to make the network interface working in real 
time mode with a non-TDMA capable remote station?
Is it possible with RTnet, does it make sense?
As the communication is already working with a definite rhythm, I think the TDMA 
functionality is not necessarily required. Is this true?


I thought about the steps mentioned in this thread or changing the rtnet start 
script:
http://www.mail-archive.com/[email protected]/msg02187.html

However I am not sure which commands are required and which are not, to set up 
the interface.
The basic/standard installation of RTnet worked so far.

Thanks and kind regards
Vinzenz Bargsten

    

  

  
Regards

Anders
  







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