Synchronization

When writing reactive code that needs to send a new command every cycle, or use fresh sensor data, it can be helpful to synchronize with ALMotion's cycles.

Cycle events

preProcess event
sensor data is refreshed from memory
cartesian data is updated and available
interpolation tasks provide their new intentions
set and change commands provide their new intentions
intentions are executed on the model
intentions are sent to the DCM
postProcess event
sleep

The motion thread uses a real time priority just lower than the DCM, and will try to execute on the anniversary of start up time + CycleNumber * 20ms. Should we fall behind by more than 20ms we will stop trying to catch up, and continue from the present.

Using cycle events

From a NAOqi module, perhaps made with the module generator, you have access to the broker, and can use it to create a connection to Motion's preProcess or postProcess events. This allows to be woken at the beginning or end of each cycle to do some processing: get the current state of the robot, and prepare some commands.



          // Your method that will be called
          void YourModule::motionPreProcessCallback() {
            // Do something very small every 20ms.
            // You are in a real time thread, so beware.
            // If you wish to do heavy processing, you should
            // raise a signal that is consumed by another thread
          }

          void YourModule::subscribeMotionPreProcess() {
          try {
            // Register the callback
            // The specialized proxy does not give access
            // to the underlying module needed for this binding,
            // so we get a generic proxy from the parent broker
            getParentBroker()->getProxy("ALMotion")->getModule()->atPreProcess(
               boost::bind(&YourModule::motionPreProcessCallback,this));
                
            } catch(const AL::ALError& e) {
               std::cout << "Motion preProcess callback registration failed" << std::endl;
            }
           }

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