Re: [ros-users] [Orocos-users] Joint controller manager

On Mon, 4 Feb 2013, Wim Meeussen wrote:

>> I'd like to bring up the subject of having controllers running at lower
>> rates than the controller_manager. I can think of two possible solutions:
>>
>> 1. Frequency divider:
>> ...
>
>> 2. Individual/grouped controller updating:
>> ...
>>
>> At the moment I'm leaning towards the frequency divider as it is sufficient
>> for our use cases. I wonder if someone has a use case that does not fit well
>> with this approach.
>
> Some comments specifically targeted at the current implementation of
> the controller manager:
>
> While I see the frequency divider approach has a number of
> limitations, it makes it very easy to implement the realtime loop
> around the controller manager.  It basically looks something like
> this:
>
> main()
> {
>  MyRobot robot;
>  ControllerManager cm(&robot);
>
>  while (true)
>  {
>     robot.read();
>     cm.update(getTime(), period);
>     robot.write();
>     sleepRemainingPeriod();
>  }
> }
>
> When judging other approaches, it would be great if we can look back
> and see how they affect the usage pattern of the controller manager.
>
> When applying this test to the approach where each controller
> specifies its required update rate, at first glance it looks like we
> could keep the realtime loop pretty simple. Based on all the desired
> update rates, the controller manager could compute the desired
> sleep/wakeup time between different controller runs, and expose this
> duration/time to the person writing the realtime loop. I'm not sure
> yet what the exact implementation details would look like for
> different realtime OS's, or when using the controller manager with
> RTT. Could someone shed some light on how they intend to use the
> controller manager with RTT?

A TaskContext with a "timer port", and running the scheduler inside.

> Best,
> Wim

Herman
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