My two cents: maybe allowing single controllers to return the expected time they want to be updated given their own internal state. With this information control manager will adapt its own rate depending on the earliest deadline of the controllers it manages. On Thu, Jan 31, 2013 at 12:55 PM, Adolfo Rodríguez Tsouroukdissian wrote: > All, > > 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: > - Individual controller configurations can specify an optional parameter > that states the desired frequency, or that work should be done only '1 out > of n' manager cycles. > - Pros: Easy to implement. It is specific to a particular controller > implementation, hence does not need to be part of the controller_manager > library. See [1] for an example. > - Cons: Desired controller update period is subject to an error of up to one > controller manager control period. > > 2. Individual/grouped controller updating: > - The controller manager allows the option of updating single controllers, > or groups of them. Triggering these updates is not handled by the manager. > - Pros: Desired controller update period is unaffected by the controller > manager's update period. > - Cons: This solution requires significant changes to the existing > controller_manager codebase: > - Extending the API to allow not only batch update()s, but also updates to > a subset of the running controllers. Resolving which controllers to update > should be a constant-time operation. > - Add protection against concurrent access to data (eg. simultaneous > read() and update()), possibly with lock-free data structures. > - Because of the above point, the chosen concurrency handling mechanism > might render reusing the existing standard hardware interfaces impossible > (lock-free structures usually expose data through accessors, not raw > pointers). > > 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. > > [1] > https://github.com/willowgarage/ros_controllers/blob/master/joint_state_controller/src/joint_state_controller.cpp#L78 > > > -- > Adolfo Rodríguez Tsouroukdissian > Senior robotics engineer > adolfo.rodriguez@pal-robotics.com > http://www.pal-robotics.com > > PAL ROBOTICS S.L > c/ Pujades 77-79, 4º4ª > 08005 Barcelona, Spain. > Tel. +34.93.414.53.47 > Fax.+34.93.209.11.09 > Skype: adolfo.pal-robotics > Facebook - Twitter - PAL Robotics YouTube Channel > > AVISO DE CONFIDENCIALIDAD: Este mensaje y sus documentos adjuntos, pueden > contener información privilegiada y/o confidencial que está dirigida > exclusivamente a su destinatario. Si usted recibe este mensaje y no es el > destinatario indicado, o el empleado encargado de su entrega a dicha > persona, por favor, notifíquelo inmediatamente y remita el mensaje original > a la dirección de correo electrónico indicada. 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