Sample code explanation

Sample code explanation

We will now add the NXTBrick.py functionality to the generated component.

  • NXTBrick.py import: Import the NXTBrick.py file to get access to the NXTBrick class. The file extension is not necessary in the import statement.

 import NXTBrick

  • Implement onInitialize(self): In onInitialize(), instantiate the NXTBrick class. If this causes an error, return RTC_ERROR and the component will transition to the end state.
            # create NXTBrick object
            try:
                self._nxtbrick = NXTBrick.NXTBrick()
            except:
                print "NXTBrick create failed."""
                return RTC.RTC_ERROR
  • Implement onActivated(self, ec_id) and onDeactivated(self, ec_id): In onActivated() and onDeactivated(), the NXTBrick class's resetPosition() method should be called.
            self._nxtbrick.resetPosition() 
  • Implement onExecute(self, ec_id): The following steps should be performed by onExecute():
    • Read speeds from the data InPort
    • Based on configuration values, which port of the NXT the speed values are to be sent to should be set.
    • Call the setMotors() method of the NXTBrick class to set motor speeds.
    • Call the getSensors() method of the NXTBrick class to read the ultrasonic sensor data, and write this to an OutPort.
    • Call the getMotors() method of the NXTBrick class to get the motor encoder angles, and write this to an OutPort.

Code that implements the above functionality is shown below:

 #!/usr/bin/env python
 # -*- coding:shift_jis -*-
 # -*- Python -*-
 
 import sys
 import time
 sys.path.append(".")
 
 # Import RTM module
 import OpenRTM
 import RTC
 
 
 # import NXTBrick class
 import NXTBrick
 
 
 # This module's spesification
 # <rtc-template block="module_spec">
 nxtrtc_spec = ["implementation_id", "NXTRTC", 
          "type_name",         "NXTRTC", 
          "description",       "NXT sample component", 
          "version",           "0.1", 
          "vendor",            "AIST", 
          "category",          "example", 
          "activity_type",     "DataFlowComponent", 
          "max_instance",      "10", 
          "language",          "Python", 
          "lang_type",         "SCRIPT",
          "conf.default.map", "A,B",
          ""]
 
 # </rtc-template>
 
 class NXTRTC(OpenRTM.DataFlowComponentBase):
     def __init__(self, manager):
         OpenRTM.DataFlowComponentBase.__init__(self, manager)
 
         # DataPorts initialization
         # <rtc-template block="data_ports">
         self._d_vel = RTC.TimedFloatSeq(RTC.Time(0,0),[])
         self._velIn = OpenRTM.InPort("vel", self._d_vel, OpenRTM.RingBuffer(8))
         self.registerInPort("vel",self._velIn)
         self._d_pos = RTC.TimedFloatSeq(RTC.Time(0,0),[])
         self._posOut = OpenRTM.OutPort("pos", self._d_pos, OpenRTM.RingBuffer(8))
         self.registerOutPort("pos",self._posOut)
         self._d_sens = RTC.TimedFloatSeq(RTC.Time(0,0),[])
         self._sensOut = OpenRTM.OutPort("sens", self._d_sens, OpenRTM.RingBuffer(8))
         self.registerOutPort("sens",self._sensOut)
 
         # initialize of configuration-data.
         # <rtc-template block="configurations">
         self._map = [['A', 'B']]
         self._nxtbrick = None
         self._mapping = {'A':0,'B':1,'C':2}
          
     def onInitialize(self):
         # Bind variables and configuration variable
         # <rtc-template block="bind_config">
         self.bindParameter("map", self._map, "A,B")
 
         # create NXTBrick object
         try:
             print "Connecting to NXT brick ...."
             self._nxtbrick = NXTBrick.NXTBrick()
             print "Connection established."
         except:
             print "NXTBrick connection failed."
             return RTC.RTC_ERROR
 
         return RTC.RTC_OK
 
     def onFinalize(self):
         self._nxtbrick.close()
 
 
     def onActivated(self, ec_id):
         # reset NXTBrick's position.
         self._nxtbrick.resetPosition()
 
         return RTC.RTC_OK
 
     def onDeactivated(self, ec_id):
         # reset NXTBrick's position.
         self._nxtbrick.resetPosition()
 
         return RTC.RTC_OK
 
     def onExecute(self, ec_id):
         cnt = 0
         # check new data.
         if self._velIn.isNew():
             # read velocity data from inport.
             self._d_vel = self._velIn.read()
             vel_ = [0,0,0]
             vel_[self._mapping[self._map[0][0]]] = self._d_vel.data[0]
             vel_[self._mapping[self._map[0][1]]] = self._d_vel.data[1]
             # set velocity
             self._nxtbrick.setMotors(vel_)
 
         # get sensor data.
         sensor_   = self._nxtbrick.getSensors()
         if sensor_:
             self._d_sens.data = sensor_
             self._sensOut.write()
 
         # get position data.
         position_ = self._nxtbrick.getMotors()
         if position_:
             self._d_pos.data =                  [position_[self._mapping[self._map[0][0]]][9],                       position_[self._mapping[self._map[0][1]]][9]]
         # write position data to outport.
         self._posOut.write()
 
         return RTC.RTC_OK
 
 
 
 def MyModuleInit(manager):
     profile = OpenRTM.Properties(defaults_str=nxtrtc_spec)
     manager.registerFactory(profile,
                             NXTRTC,
                             OpenRTM.Delete)
 
     # Create a component
     comp = manager.createComponent("NXTRTC")
 
 
 
 def main():
     mgr = OpenRTM.Manager.init(len(sys.argv), sys.argv)
     #mgr = OpenRTM.Manager.init(sys.argv)
     mgr.setModuleInitProc(MyModuleInit)
     mgr.activateManager()
     mgr.runManager()
 
 if __name__ == "__main__":
     main()

Sample code explanation (Callback object usage example)

This sample code adds a callback, OnWrite, to the above sample. When data is written to the InPort's buffer, the motor's speeds will be set immediately.

  • Callback class
    Create a callback class as below.

 # @class CallBackClass
 # @brief callback class
 #
 # when data is written in the buffer of InPort,
 # it is called.
 class CallBackClass:
     def __init__(self, nxtbrick_, map_):
         self._nxtbrick = nxtbrick_
         self._map = map_
         self._mapping = {'A':0,'B':1,'C':2}
 
     def __call__(self, pData):
         vel_ = [0,0,0]
         vel_[self._mapping[self._map[0][0]]] = pData.data[0]
         vel_[self._mapping[self._map[0][1]]] = pData.data[1]
         # set velocity
         self._nxtbrick.setMotors(vel_)

This class receives a NXTBrick instance and a configuration parameter map in its constructor.

  • Callback class registration
    Use the setOnWrite() method to register a CallBackClass instance with the component.

   # set callback class
   self._velIn.setOnWrite(CallBackClass(self._ntxbrick,self._map))

After this call to setOnWrite(), whenever data is written to the InPort, CallBackClass.call() will be called.

Sample code that implements the complete component using a callback class is shown below.

 #!/usr/bin/env python
 # -*- coding:shift_jis -*-
 # -*- Python -*-
 
 import sys
 import time
 sys.path.append(".")
 
 # Import RTM module
 import OpenRTM
 import RTC
 
 
 # import NXTBrick class
 import NXTBrick
 
 
 # This module's spesification
 # <rtc-template block="module_spec">
 nxtrtc_spec = ["implementation_id", "NXTRTC", 
          "type_name",         "NXTRTC", 
          "description",       "NXT sample component", 
          "version",           "0.1", 
          "vendor",            "AIST", 
          "category",          "example", 
          "activity_type",     "DataFlowComponent", 
          "max_instance",      "10", 
          "language",          "Python", 
          "lang_type",         "SCRIPT",
          "conf.default.map", "A,B",
          ""]
 
 # </rtc-template>
 
 # @class CallBackClass
 # @brief callback class
 #
 # when data is written in the buffer of InPort,
 # it is called.
 class CallBackClass:
     def __init__(self, nxtbrick_, map_):
         self._nxtbrick = nxtbrick_
         self._map = map_
         self._mapping = {'A':0,'B':1,'C':2}
 
     def __call__(self, pData):
         vel_ = [0,0,0]
         vel_[self._mapping[self._map[0][0]]] = pData.data[0]
         vel_[self._mapping[self._map[0][1]]] = pData.data[1]
         # set velocity
         self._nxtbrick.setMotors(vel_)
 
 
 class NXTRTC(OpenRTM.DataFlowComponentBase):
     def __init__(self, manager):
         OpenRTM.DataFlowComponentBase.__init__(self, manager)
 
         # DataPorts initialization
         # <rtc-template block="data_ports">
         self._d_vel = RTC.TimedFloatSeq(RTC.Time(0,0),[])
         self._velIn = OpenRTM.InPort("vel", self._d_vel, OpenRTM.RingBuffer(8))
         self.registerInPort("vel",self._velIn)
         self._d_pos = RTC.TimedFloatSeq(RTC.Time(0,0),[])
         self._posOut = OpenRTM.OutPort("pos", self._d_pos, OpenRTM.RingBuffer(8))
         self.registerOutPort("pos",self._posOut)
         self._d_sens = RTC.TimedFloatSeq(RTC.Time(0,0),[])
         self._sensOut = OpenRTM.OutPort("sens", self._d_sens, OpenRTM.RingBuffer(8))
         self.registerOutPort("sens",self._sensOut)
 
         # initialize of configuration-data.
         # <rtc-template block="configurations">
         self._map = [['A', 'B']]
         self._nxtbrick = None
         self._mapping = {'A':0,'B':1,'C':2}
          
     def onInitialize(self):
         # Bind variables and configuration variable
         # <rtc-template block="bind_config">
         self.bindParameter("map", self._map, "A,B")
 
         # create NXTBrick object
         try:
             print "Connecting to NXT brick ...."
             self._nxtbrick = NXTBrick.NXTBrick()
             print "Connection established."
         except:
             print "NXTBrick connection failed."
             return RTC.RTC_ERROR
 
         # set callback class
         self._velIn.setOnWrite(CallBackClass(self._ntxbrick,self._map))
 
         return RTC.RTC_OK
 
     def onFinalize(self):
         self._nxtbrick.close()
 
     def onActivated(self, ec_id):
         # reset NXTBrick's position.
         self._nxtbrick.resetPosition()
 
         return RTC.RTC_OK
 
 
     def onDeactivated(self, ec_id):
         # reset NXTBrick's position.
         self._nxtbrick.resetPosition()
 
         return RTC.RTC_OK
 
 
     def onExecute(self, ec_id):
         # get sensor data.
         sensor_   = self._nxtbrick.getSensors()
         if sensor_:
             self._d_sens.data = [sensor_[3]]
             # write sensor data to outport.
             self._sensOut.write()
 
         # get position data.
         position_ = self._nxtbrick.getMotors()
         if position_:
             self._d_pos.data = [position_[self._mapping[self._map[0][0]]][9],position_[self._mapping[self._map[0][1]]][9]]
             # write position data to outport.
             self._posOut.write()
 
         return RTC.RTC_OK
 
 
 
 def MyModuleInit(manager):
     profile = OpenRTM.Properties(defaults_str=nxtrtc_spec)
     manager.registerFactory(profile,
                             NXTRTC,
                             OpenRTM.Delete)
 
     # Create a component
     comp = manager.createComponent("NXTRTC")
 
 
 
 def main():
     mgr = OpenRTM.Manager.init(len(sys.argv), sys.argv)
     #mgr = OpenRTM.Manager.init(sys.argv)
     mgr.setModuleInitProc(MyModuleInit)
     mgr.activateManager()
     mgr.runManager()
 
 if __name__ == "__main__":
     main()
 

In the first example, the motor output, sensor reading and motor encoder reading are all done in a single synchronous loop. By using a callback, the motor output is done asynchronously when data arrives.

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