We have about 50us of jitter in our realtime loop, and it isn't a problem for us, but our robot is also statically stable. We're currently using the 3.0.6-rt17 kernel, which is a bit old at this point, but it has proven more stable than the previous PR2 kernel. My configuration is set up with a minimal number of drivers built into the kernel, and with a large number of USB device drivers built as modules. Since we use NFS on the PR2, there are a number of NFS-related things enabled; and probably a few other obscure things we use that most other users don't need. Before you worry too much about the remaining jitter in your system, I would try to determine how much jitter is acceptable. This seems to have some ideas on where to start in that process: http://www.cs.st-andrews.ac.uk/~pn/establishing-timing-reqs-mm02.pdf If you find that you need lower jitter, I would ask on Linux RT users mailing list: linux-rt-users@vger.kernel.org Regards, -Austin On 04/10/2012 01:35 PM, Soo-Hyun Yoo wrote: > Hello Austin, > > Would you be willing to share your PREEMPT_RT kernel configuration > file for the PR2? I have tried disabling all unnecessary (in my > judgment, which could be wrong!) features for kernel v3.0.25 patched > with PREEMPT_RT v44, but the EtherLab Master node still suffers from a > jitter of around 60 us. > > Does that sounds reasonable? The high jitter could just be due to our > use of an Intel Atom processor compared to the PR2's Core i7's, but I > don't know how (if at all) that would affect the jitter. What kind of > jitter do you get on the PR2? > > Soo-Hyun Yoo > > On Wed, Jan 11, 2012 at 11:56 AM, Austin Hendrix > wrote: > > This sounds nearly identical to the system we use here at Willow > Garage on the PR2. > > We're using a PREEMPT_RT kernel (2.6.31+, moving to 3.0) with a > 1kHz control loop in user space. > > -Austin > > Jonathan Hurst > wrote: > > >Dear ROS Users, > > > >We would like to use Robot Operating System on ATRIAS, the bipedal > >robot we are building > >(http://mime.oregonstate.edu/research/drl/Site%20Pages/Atrias.html), > >but we must have reliable real-time control at 1kHz with > communication > >over an EtherCAT bus. We have assembled some existing software tools > >to enable this, including the EtherLab driver and Orocos RTT to tie > >things all together in real time. If you are interested in this > >discussion, please feel free to join the Email list - it has a brief > >history with one or two summaries of working systems, but I hope we > >will have much more detailed discussions, or receive pointers to > other > >working systems. You can sign up for the list here: > >https://secure.engr.oregonstate.edu/mailman/listinfo/ethercat-ros > > > >Jonathan > >-- > >***************************************************************************** > >Jonathan W. Hurst > >Assistant Professor > >School of Mechanical, Industrial, and Manufacturing Engineering > >Oregon State University > >204 Rogers Hall > >Corvallis, OR 97331-6001 > > > >jonathan.hurst@oregonstate.edu > > >Voice: (541) 737-7010 > >Fax: (541) 737-2600 > >http://mime.oregonstate.edu/research/jhurst/ > >****************************************************************************** > >_______________________________________________ > >ros-users mailing list > >ros-users@code.ros.org > >https://code.ros.org/mailman/listinfo/ros-users > _______________________________________________ > ros-users mailing list > ros-users@code.ros.org > https://code.ros.org/mailman/listinfo/ros-users > >