I have an other concern, what will happen if processing of trajectory take more time than remaining to first point of new trajectory.
Pozdrawiam
Konrad Banachowicz
Hi,
The buffer used in the JointSplineTrajectoryController is called a
On Fri, Sep 17, 2010 at 12:53 PM, Konrad Banachowicz <konradb3@gmail.com> wrote:
> yes RT and non-RT work execute in separated threads but what about shared
> data ? as far as i know there is some locking involved ?
RealtimeBox. It currently uses a mutex (locked for a guaranteed
maximum number of instructions on a system that supports priority
inheritance), though it can certainly switch to a lock-free buffer.
Sounds like you've moved the non-realtime parts of the
> Communication between RT and non-RT threads is complex problem, but OROCOS
> solves most problems. it use lock-free buffers for communication between
> components. Currently in ROS joint_trajectory_action is whole non-RT and
> JointSplineTrajectoryControlle is partialy RT. In my solution all non-RT
> work are moved into joint_trajectory_action. This make clear border between
> RT and non-RT part.
JointSplineTrajectoryController into your version of the
joint_trajectory_action. That sounds like a reasonable solution.
-Stu
>
> Pozdrawiam
> Konrad Banachowicz
>
>
> 2010/9/17 Stuart Glaser <sglaser@willowgarage.com>
>>
>> Hi Konrad,
>>
>> There are no issues with breaking realtime constraints because the
>> unsafe code is called from a non-realtime thread.
>>
>> You're correct that the JointSplineTrajectoryController code performs
>> several operation which are not realtime safe. These operations are
>> performed not in the realtime loop but rather in the ROS subscriber
>> callback, which is called from a non-realtime thread.
>>
>> Your proposed solution is therefore quite similar to what already
>> exists: the non-realtime portion of the
>> JointSplineTrajectoryController reorders the joints and composes
>> trajectories, and then sends it to the realtime portion which just
>> performs interpolation.
>>
>> There are a few faults with this system, and I'm interested in
>> discussing solutions which address them:
>> 1. Trajectories cannot be sent from within realtime--they only come
>> from outside of realtime.
>> 2. The current design has a great deal of complexity, particularly in
>> taking care when transferring the trajectory to realtime, composing
>> trajectories, and responding with a result to the action.
>>
>> There's probably more.
>>
>> That said, this interface allows us to comfortably separate the motion
>> planning pipeline from the realtime loop. Once implemented, you can
>> run much of the code that was developed to move the PR2 on your own
>> robot.
>>
>> Lastly, you may want to consider examining the
>> JointTrajectoryActionController which combines the
>> joint_trajectory_action and the JointSplineTrajectoryController.
>>
>> -Stu
>>
>> On Fri, Sep 17, 2010 at 3:12 AM, Konrad Banachowicz <konradb3@gmail.com>
>> wrote:
>> > Hi,
>> > I'm working on integration of orocos RT-controller with ROS manipulation
>> > pipeline.
>> > I already done joint_state_publisher and oro_action_server. Next on my
>> > list
>> > are joint_trajectory_action and JointSplineTrajectoryController.
>> > I have some concerns about real-time behaviours of those, and way of
>> > implementation in orocos.
>> >
>> > joint_trajectory_action :
>> > It receive goal containing trajectory (variable size, unbounded size),
>> > then
>> > check constraints and send to JointSplineTrajectoryController.
>> >
>> > JointSplineTrajectoryController:
>> > It loop generating interpolated position for joint regulator.
>> > When it receive new trajectory it reorder joints in received trajectory
>> > (memory allocation, iterating on unknown size array) and try to compose
>> > current trajectory with newly received (memory allocation, iterating on
>> > unknown size array).
>> > It have to by done between two sequential interpolations (in my system
>> > 1ms).
>> >
>> > My solution :
>> > Data transmited between joint_trajectory_action and
>> > JointSplineTrajectoryController contains only single point (constant
>> > size).
>> >
>> > joint_trajectory_action do joint reordering and compose trajectories and
>> > is
>> > feeding JointSplineTrajectoryController with trajectory points.
>> >
>> > JointSplineTrajectoryController interpolate between two points (have one
>> > point buffer)
>> >
>> > This solution should work with trajectories when time between points is
>> > >>
>> > 1ms.
>> >
>> > What do you think about doing this this way ?
>> > What is alternative solutions ?
>> > What do you think about re-usability of this solution in yours systems ?
>> >
>> > Pozdrawiam
>> > Konrad Banachowicz
>> >
>> > _______________________________________________
>> > ros-users mailing list
>> > ros-users@code.ros.org
>> > https://code.ros.org/mailman/listinfo/ros-users
>> >
>> >
>>
>>
>>
>> --
>> Stuart Glaser
>> sglaser -at- willowgarage -dot- com
>> www.willowgarage.com
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>> https://code.ros.org/mailman/listinfo/ros-users
>
>
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>
--
Stuart Glaser
sglaser -at- willowgarage -dot- com
www.willowgarage.com
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