ORTE communication middleware for Android OS Martin Vajnar
Contents
1. 18 5 3 User Manual In order to reduce the high frequency component we use a simple filter that takes the previous value of acceleration yn 1 the current measured value u n and calculates new value of acceleration y n Eq 5 1 where a 0 75 We apply this formula to both the x axis and y axis component of the acceleration vector This filter is mentioned in the documentation of the SensorEvent API 1 This filtered acceleration vector is then used to calculate the required speeds of the left and right motor of the robot B 5 2 3 Handling of received Laser Range Finder Data 2 all 17 53 RoboDruid Figure 5 7 Visualization of Data published by the LRF The Laser Range Finder produces data in polar coordinates The space around the LRF is partitioned into equally sized circular sectors There are 681 values published through the hokuyo_scan topic Each value contains distance to the nearest obstacle in millimeters in a specific circular sector This data is easily transformed to a Cartesian coordinate system that is used by Android s painting methods Example of the visualized LRF data in the RoboDruid is on Figure 5 7 E 5 3 User Manual Since the RoboDruid is intended for demonstration purposes we present a thorough step by step guide for RoboDruid s compilation Section 5 3 1 on Debian like OS s as well as RoboDruid s user manual Section 5 3 2 19 5 Demo application2. Example Java Manager Example Java Data type Example Java Publisher Example Java Subscriber Relative slowdown of imple mentationS IDL code for topic motion IDL code for topic pwr VOM AGC sg adie an alk m inde kn le v e IDL code for topic hokuyo IDL code for topic magnet GIG e Renoir dier oc EE ence frame eet ER E ISIE oloo JC OS mei ete Chapter 1 Introduction Real Time applications often need to be distributed over multiple computing nodes Reasons for that include the distribution of the computing power to the places where it is needed or simplification of the design management or maintenance of the appli cation The vital part of all distributed applications is the communication between the application components running on different nodes In case of real time applications the communication is subject to temporal constraints such as deadlines Applications often need to be fault tolerant and as such they must support redundancy in their architecture Another common requirement is dynamic nature of the application where nodes components are joined to or removed from the application at run time These often contradicting requirements make the communication part hard to design and implement For this reason people often build their application on top of various communication middleware platforms that handle the communica
3. E 5 3 1 Compilation In order to compile RoboDruid on Debian based systems the following packages must be installed a make version 3 81 or higher s ant m git a oracle java7 installer As a next step download Android NDK and SDK After extracting these you need to launch shell and add few directories to the PATH environment variable export PATH PATH path to NDK export PATH PATH lt path to SDK gt platform tools lt path to SDK gt tools Next it is necessary to obtain SDK Platform for Android 4 0 3 To do this execute command android update sdk no ui all filter android 15 During the installation user has to accept the Android Software Development Kit License Agreement In the next step source code of ORTE and RoboDruid will be fetched There are many ways to accomplish that I suggest cloning the GIT repository You do this by issuing git clone git rtime felk cvut cz orte cd orte In the next step a local properties file will be created for both the Android library and the RoboDruid application android update project p orte libaorte android update project p orte contrib Robot Demo To build the native code you have to issue the following commands cd orte libaorte ndk build Now it is possible to build the Java code and sign the application package with a debug key cd contrib Robot Demo ant debug At this point user should have successfully build a pac
4. The reason for Java subscriber being slow is mostly because of the way Java receive callback is called from the native code There is a native receive thread that handles received packets as they arrive If new data were received a native callback function is called from within this thread The callback is passed a buffer containing the received data as well as an instance of ORTERecvInfo structure containing information about the data e g endianess topic sequence number In case of Java subscribers this callback is implemented as a JNI function that first attaches itself to the Java VM to have access to Java classes and existing objects It then creates a new Java object that is essentially a Java version of the ORTERecvInfo structure After this it sets byte order of Java s direct ByteBuffer according to ORTERecvInfo and calls a method of an Java object which represents the received data to deserialize the data stored in the ByteBuffer When this is done an application callback function is called with the deserialized Java object as a parameter After the Java callback returns the native receive thread detaches itself from the Java VM As could be seen from the above description the main bottleneck lays in the fact that the native receive thread from which the Java wrapper s receive callback function is called has to be attached to the Java VM and has to call many JNI functions that copy a lot of data internally As could be seen from perfor
5. or that it wants to receive subscribe to such a data The underlying middleware ensures that the stream of data is properly communicated from one or more producers to one or more subscribers Besides the basic data exchange between publishers and subscribers the middleware allows the applications to specify many additional Quality of Service QoS parameters such as deadlines reliability level data durability etc This not only simplifies the application design but also allows the middleware to optimize the communication in many ways The DDS standard specifies only the API not the underlying mechanisms that implement the data exchange The communication protocol that can be used to implement the functionality re quired by the DDS API is called the Real Time Publish Subscribe RTPS protocol 9 The primary goal of RTPS is to provide interoperability between different DDS mid dleware platforms This is achieved by defining a minimal set of requirements that all implementations have to satisfy Besides that the standard defines many optional advanced features as well as a way for implementing vendor specific extensions of the protocol The standard defines the protocol in a platform transport independent way and then it defines the mapping onto the UDP IP protocol The protocol takes ad vantage of multicast communication when available but works also in environments without multicast support Implementations can decide about trade offs in re
6. and MulticastLock B 3 5 Java Manager Evaluation L Example Android Applica 2 Performance Comparison Demo application L Demo Robot 4 Robot s Hardware Robot s Software Mapping of CAN Mes sage IDs to ORTE Top PEE Implementation 2 1 Java Package Structure 2 2 Acquisition and Pro cessing of Accelerome ter d lka asd rdk ked 5 2 3 Handling of received Laser Range Finder DALA iter RR REPRE 5 3 User Manual Compilation User Instructions Conclusion uuusuuue References Abbreviations Contents of the Attached CD po w E Im G1 Tables Figures Mapping of ORTE objects to similar objects in the RTPS V E t bir cr M B Comparison of Wi Fi ping latencies with and without WifiLock OMNE Performance comparison of native code and Java wrapper Mapping of CAN Message IDs to ORTE Wopies 2 27 IDL code for topic crane cmd Android Sensor API refer Visualization of LRF Data RoboDruid s default screen RoboDruid s menu RoboDruid s Voltage Monitor RoboDruid s Managers Dia l Data Centric Publish Subscribe application model Picture of mobile robot
7. as well as the name SSID of the Wi Fi network that the device is currently connected to After entering IP addresses of neighboring computers in the box confirm new settings by tapping OK After this a new manager domain will be created It will take approximately one minute for applications running on nodes across the network to find each other through the newly created manager domain If you do not want to wait just restart RoboDruid It will remember the list of neighboring computers across restarts As this application is intended for demonstration purposes unexpected situations can occur such that could lead to robot s damage or cause an injury to someone In case of such an event pressing the Home or Power button will stop robot s movement 23 Chapter 6 Conclusion In this work an application to monitor and control mobile robots using an Android based mobile device was developed This application can be used on occasions like Doors Open Days In order to develop the application we first had to port the ORTE library to Android We successfully ported the ORTE library and it s Java wrapper to Android As a result many bugfixes and changes were made to the Java wrapper the most important being m Creation of Java variant of the ORTE Manager a Ability to receive and publish data in both Little Endian and Big Endian byte orders a Reduction of overhead during data s publication reception achieved by eliminating excessiv
8. being the possibility to publish new data Java specification do not offer a data type specifically intended for storing pointers like the C types intptr t ptrdiff t or size_t so initially pointers were stored in the Java s int type which is 32 bit wide This works well on current versions of Android because most devices use 32 bit ARM based CPU but does not work if used with Oracle s VM on a 64 bit OS In order to overcome this we use long fields 64 bit to store pointers instead of int fields This is also the recommended way by Google 4 64 bit Considerations to store pointers on Android E 3 3 4 Use of WifiLock and MulticastLock Android makes extensive use of power saving features One of them is the Wi Fi Power Save Polling PSP mode 6 When this mode is entered the device asks Wi Fi Access Point to cache all the downlink frames intended for that device Cached frames could be delivered during a wake up mode that is entered either in order to transmit data or to 1 For implementation see http rtime felk cvut cz gitweb orte git commit 5e3acad2883da79c29458d5965d3dad8cbf 629f7 http rtime felk cvut cz gitweb orte git commit 8a64c855d6b3938310493987 7d3248571d949c71 For implementation see http rtime felk cvut cz gitweb orte git commit b0dec948790009768c3e9fdc7a904 2056c945a9 3 Porting to Android retrieve cached data Wake up mode could be also entered by sending a PS Poll frame After t
9. protocol for applications based on the Data Distribution Service DDS API RTPS is widely used in many industrial applications and it has both commercial and open source implementations One open source implementation is called Open Real Time Ethernet ORTE and it is known to work on many plat forms including GNU Linux Windows FreeBSD and MacOS In this thesis a new addition to the supported plat forms is described which is an Android operating system for mobile devices We provide an overview of the steps that were needed to port the protocol to the Android platform I ported the ex isting native library and a Java wrapper around it We comment on the troubles I had and their solutions We compare the performance of ORTE on Android with other platforms and present an An droid phone application for controlling and monitoring a mobile robot Keywords DCPS DDS RIPS ORTE Android OS Java Native Inter face real time communication Contents Introduction 3x kxx eu fne 2 DDS RTPS and ORTE 3 2 1 Compatibility of ORTE with the Latest RTPS standard 4 Mapping of objects in ORTE to the RTPS V2 1 List of required changes to ORTE 3 Porting to Android 3 1 Android Permission Model 3 2 Overview of the porting pro 3 3 Technical Details 3 1 Class Loading Direct ByteBuffer 64 bit Support Use of WifiLock
10. 7 Object Management Group Data Distribution Service for Real time Systems Version 1 2 Online http www omg org cgi bin doc formal 07 01 01 pdf visited 5 2014 Jan 2007 8 Object Management Group Common Object Request Broker Architecture CORBA Specification Version 3 1 Part 1 CORBA Interfaces Number formal 2008 01 04 Online 2008 9 Object Management Group The Real time Publish Subscribe Wire Protocol DDS Interoperability Wire Protocol Specification DDS RTPS Online http www omg org spec DDSI RTPS 2 1 visited 5 2014 Nov 2010 10 OpenDDS OpenDDS web site Online http www opendds org visited 5 2014 11 Oracle Corp Java Platform SE 7 ByteBuffer documentation Online http docs oracle com javase 7 docs api java nio ByteBuffer html visited 5 2014 12 Oracle Corp Java SE Documentation JNI Functions Online http docs oracle com javase 7 docs technotes guides jni spec functions html visited 5 2014 13 Luk Pokorn Podp rn n stroje pro RTPS komunikaci Master s thesis Fakulta elektrotechnick VUT 2005 14 Real Time Innovations Inc RTPS Wire Protocol Specification Version 1 0 On line 25 References http orte sf net rtpsi 2 pdf visited 5 2014 Feb 2002 Draft Document Version 1 17 15 Petr Smol k and Pavel P a ORTE The Open Real Time Ethernet Technical report Czech Technical Unive
11. Bachelor s Thesis Czech Technical University in Prague F3 Faculty of Electrical Engineering Department of Control Engineering ORTE communication middleware for Android OS Martin Vajnar Cybernetics and Robotics Systems and Control May 2014 Supervisor Ing Michal Sojka Ph D esk vysok u en technick v Praze Fakulta elektrotechnick katedra dic techniky ZAD N BAKAL SK PR CE Student Martin Vajnar Studijn program Kybernetika a robotika Obor Syst my a zen N zev t matu Komunika n middleware ORTE pro OS Android Pokyny pro vypracov n 1 Seznamte se komunika n m middlewareem ORTE vyvinut m na kated e kter implementuje komunika n protokol Real Time Publish Subscribe RTPS D le se seznamte s aplikac ORTE v dic m syst mu mobiln ch robot 2 Portujte ORTE na mobiln za zen s opera n m syst mem Android 3 Vyvi te aplikaci pro mobiln telefony kter bude umo ovat sledovat a ovl dat mobiln m telefonem roboty 4 Analyzujte rozd ly mezi aktu ln implementac ORTE a nov j mi verzemi RTPS standardu Navrhn te jak zm ny je pot eba v ORTE prov st aby bylo kompatibiln s RTPS standardem 5 V e pe liv otestujte a zdokumentuje Seznam odborn literatury 1 Object Management Group The real time publish subscribe wire protocol DDS interoperability wire protocol specification DDS RTPS Online http www omg or
12. CSChangeFromWriter ChangeFromWriter 8 4 10 5 description 8 4 12 3 illustration CSChange CacheChange 8 2 3 CSChangeForReader ChangeForReader 8 4 7 6 description 8 4 9 3 illustration CSTRemoteReader ReaderProxy 8 4 7 5 CSTWriter Stateful Writer 8 2 7 description 8 4 7 implementation Table 2 1 Mapping of ORTE objects to similar objects in the RTPS V2 1 standard E 2 1 2 List of required changes to ORTE By analyzing the Platform Independent Module 9 Section 8 and by comparing it with the ORTE implementation we can write a list of changes that need to be done in order for ORTE to be compatible with the RTPS V2 1 D UDPv6 support It is referrenced to as one of the kinds of transport in Locator t type For more information see 9 Table 8 2 in Section 8 2 1 2 Data with key RTPS V2 1 introduced a new type of data objects data with key This allows to distribute a set of data instances as opposed to a single data instance under a single topic A part of the data instance called a key is used to distinguish between different instances For more information see 9 Table 8 2 in Section 8 2 1 2 Stateless Readers and Writers RTPS V2 1 provides two reference implementations of Readers and Writers namely Stateless and Stateful They differ by the amount of state they store on matched remote endpoints For detailed description see 9 Sec tion 8 4 3 RTPS V1 0 uses only the Stateful variant Discovery prot
13. as the following a Update Java wrapper that uses Java Native Interface JNI and make it Android compatible a Fix bugs that have not demonstrated themselves under the Oracle s VM a Add support for Android build system a Make Java version of ORTE Manager application see Section for details about Manager to overcome problems with execution and termination of native processes 5 It is possible for two or more applications from the same developer i e signed with the same private key to share the same user ID 3 Porting to Android m 3 3 Technical Details In this section we take a closer look at some problems I faced in the process of porting the ORTE library and their solution E 3 3 1 Class Loading In order to be able to call Java object s methods or access it s fields from the C code through the JNI we first need to get the associated method ID or field ID These IDs are returned by the JNI functions GetMethodID and GetFieldID respectively These functions need to know the class of the Java object This is facilitated by the FindClass function that accepts a class name as the parameter and invokes the class loader associated with the current native function to load and link the named class 12 According to the Android Documentation 4 FAQ Why didn t FindClass find my class Android s Dalvik VM uses the loader associated with the method at the top of the interpreted stack or if there is not one the thread was just at
14. ches Details of the board can be found in 19 Section 4 3 15 5 Demo application The robot is geared by two BLDC motors controlled by so called Driver board The motors are driven by a PWM signal generated by the board Detailed description of the board can be found on pages 22 23 in 19 For demo purposes the robot was equipped with a small crane manipulator arm and an electromagnet The small crane arm is driven by a servomotor Both the servomotor and the electromagnet are controlled by so called EB board Details about this board can be found on pages 18 20 in 19 Description of the robot s manipulator design is on pages 12 13 in 19 The three previously mentioned boards PWR board Driver board EB board are connected through CAN bus to the Main Controller Board The robot is equipped with a Wi Fi router that is connected through Ethernet to the Main Controller Board We use this Wi Fi interface to connect to the robot from an Android device Details about the router can be found in 19 E 5 1 2 Robot s Software The robot s Main Controller Board is powered by a Linux based Operating System custom Linux flavor includes only basic tools like BusyBox and Dropbear SSH server for more information see 19 Section 5 1 There are few programs running on this board that we will shortly describe cand application is used to send data between the Main Controller Board and other boards con
15. e ExampleData datamsg new ExampleData appDomain example topic PublProp publProp new PublProp example topic example type persistence strength Publication pub appDomain createPublication publProp datamsg while true 1 Thread sleep 1000 pub send datamsg datamsg datat Figure 4 3 Code of a simple Java Publisher IMPOR ORR OCCA Ome i import org ocera orte types public class ExampleSubscriber extends SubscriptionCallback 1 public static void main String args throws Exception NtpTime deadline new NtpTime 10 NtpTime minSeparation new NtpTime 0 DomainApp appDomain new DomainApp 0 DomainProp defaultPropsCreate null false ExampleData datamsg new ExampleData appDomain example topic SubsProp subProps new SubsProp example topic example type minSeparation deadline ORTEConstant IMMEDIATE ORTEConstant BEST EFFORTS 0 Subscription sub appDomain createSubscription subProps datamsg new ExampleSubscriber while true Thread sleep 1000 public void callback RecvInfo info MessageData msg if info getRecvStatus ORTEConstant NEW DATA System out println ExampleData msg data Figure 4 4 Code of a simple Java Subscriber 13 4 Evaluation 50096 450 400 350 300 m Java Java m C Java A Java C 25096 200 150 100 50 0 Xperia Nexus 7 PC Figure 4 5 Relative slowdown of implementations
16. e copying of elements between internal ORTE buffers and Java wrapper buffers We assesed performance of the ported Java wrapper and compared it with that of native ORTE The ported wrapper as well as the developed mobile application were thoroughly tested We have also analyzed differences between current state of the ORTE implementation and the changes necessary for it to be compatible with the RTPS V2 1 standard Shorter version of this thesis was published at the Real Time Linux Workshop 18 24 References 1 Google Inc Android Developers SensorEvent documentation Online http developer android com reference android hardware SensorEvent html P P visited 5 2014 2 Google Inc Android Developers SensorManager documentation Online http developer android com reference android hardware SensorManager html visited 5 2014 3 Google Inc Android Security Overview Online https source android com devices tech security visited 5 2014 4 Google Inc JNI Tips Online http developer android com training articles perf jni html visited 10 2013 5 Intel Corporation Power save polling PSP causes connection issues with access points Online http www intel com support wireless wlan sb cs 006205 htm visited 10 2013 6 Laird Technologies Inc Power save polling Online http www sumnitdata com Documents Glossary knowledge center p htmlpsp visited 10 2013
17. ed import org ocera orte public class ExampleManager 1 public static void main String args Manager manager new Manager while true 1 iE al Thread sleep 1000 catch Exception e e printStackTrace d J J J Figure 4 1 Code of a simple Java Manager g 4 2 Performance Comparison To have a basic understanding about the overhead of the Java wrapper used for writing Android applications a set of experiments was conducted I created a publisher and a subscriber as applications in both C native and in Java The publisher tries to publish data as fast as possible Because both the publisher and the subscriber were configured as reliable ORTE ensures that no publication gets lost and the subscriber receives all the published data Both the publisher and the subscriber were run on the same device to measure the performance of the middleware itself rather than the 11 4 Evaluation import org ocera orte import org ocera orte types public class ExampleData extends MessageData 1 public short data 1 public ExampleData DomainApp domainApp String newTopic super this setTopic newTopic domainApp regNewDataType example_type getMaxDataLength Override public void write 1 buffer rewind buffer putShort this data Jr Override public void read 1 buffer rewind this data buffer getShort lr Override public int getMaxDataLength 1 re
18. een To start receiving data subscribe to ORTE topic hokuyo scan from robot s onboard Laser Range Finder you need to tap on the gray circular sector located in the middle of the screen Successful subscription creation will be announced by text Hokuyo LRF ON To unsubscribe tap again in the same region Successful subscription cancellation will be announced by text Hokuyo LRF OFF RoboDruid Crane up Magnet Voltage monitor Fellow managers About Exit Figure 5 9 RoboDruid s menu To control robot s motion publish topic motion speed push in the top left corner of the screen and hold until text Motion Control ON appears at the bottom of the screen 21 5 Demo application In order to monitor current speed of the robot single tap in the top left corner of the screen A text Speed Monitor ON confirming successful subscription to ORTE topic motion_speed should appear The orientation of the axis is analogous to that in Figure 5 6 The vertical axis of the displayed cross represents angular velocity of the robot The horizontal axis represents linear velocity of the robot To unsubscribe tap again in the same region Succesful subscription cancellation will be announced by text Speed Monitor OFF To change position of the robot s crane press the Menu button and select Crane see Figure 5 9 The current position of the crane is written next to it in the menu The default assumed position at RoboDru
19. elocity of a mobile robot First we will briefly look at Android s SensorManager 2 and Sen sorEvent 1 API Access to built in sensors is mediated by android hardware SensorManager class This manager allows a user to request data from a certain kind of sensor The Sen sorManager then allows to register a callback listener class that will process the re ceived data This class contains a function onSensorChanged SensorEvent event that is used for processing of new data received from the sensor and onAccuracy Changed Sensor sensor int accuracy used for notification of change in sensor s accuracy Figure 5 6 Android SensorEvent API reference frame Source iij The data from sensor is delivered to the listener inside a SensorEvent object Fig ure shows coordinate system used by Android s SensorEvent API The accelerometer measures the proper acceleration i e relative to a free fall in the device s reference frame experienced by the device For robot s motion control we only need the x axis and y axis component of the acceleration vector The data produced by the sensor is susceptible to high frequency noise caused by numerous factors Perhaps the most important being the shaking of hands and delib erate attempt to overload the robot s motors by tilting the device from side to side 1 http developer android com guide components activities html http developer android com training custom views index html
20. ents of robot are connected together This information was used during the development of the demo application for Android The mobile robot being used was previously developed by the Flamingos robotic team at the Faculty of Electrical Engineering at the Czech Technical University in Prague The robot was constructed in order to take part in Eurobot 2007 and similar indoor robotic contests Later a decision was made to construct a new robot for competitions and use the former for demonstration purposes It is being used mainly at events like Doors Open Days or various exhibitions I have made no changes to it s hardware or software design B 5 1 1 Robot s Hardware The centerpiece of the Demo Robot is Main Controller Board MCB equipped with MIDAM Shark microprocessing unit powered by Freescale MPC5200 CPU The board features CAN bus 10 100T Ethernet USB host bus Detailed description of the board can be found in 19 Section 4 5 The robot is equiped with Hokuyo URG 04LX UG01 Laser Range Finder that is ca pable of measuring distance from objects in front of the robot in polar coordinates Detailed sensor parameters can be found in 19 page 26 The LRF sensor is connected to USB bus on the Main Controller Board Power to the robot is supplied by so called PWR board This board includes three independent switching power supplies delivering voltages 3 3 V 5 V and 8 V The board continuously measures voltage levels on all three bran
21. equired and only these permissions could be utilized by the application in the future It is important to say that the permissions are not enforced by the Dalvik VM but rather they are enforced at the kernel level This way it is possible to completely sand box applications on an Android device For both the Java and the native code the same permissions apply It is therefore irrelevant whether a permission is requested through calling a specific Java function provided by the Android API or through a sys tem call from the native code Applications using ORTE on Android require permission to create network sockets android permission INTERNET More detailed description of Android s security model can be found in 3 p 3 2 Overview of the porting process I considered two possible approaches to the porting of ORTE The first involved writing a pure Java implementation of the RTPS protocol from scratch the second was to use an already existing Java wrapper which makes use of the original native ORTE library through the Java Native Interface JNI and make it Android compatible After thorough consideration I ve decided to go the Java wrapper way Mostly because the C code has been in use for quite some time and could be viewed as stable On the other hand if I had chosen to write a new implementation of the protocol it would require extensive testing and would significantly slow the porting process In a nutshell the process of porting w
22. g spec DDS RTPS 2 1 Nov 2010 2 P Smol k and P P a ORTE The Open Real Time Ethernet Czech Technical University in Prague Tech Rep 2008 Online http orte sf net rtn08 orte pdf Vedouc Ing Michal Sojka Ph D Platnost zad n do konce letn ho semestru 2014 2015 prof Ing Michael DrSc vedouci katedry V Praze dne 30 1 2014 Translation of the Czech version of the Bachelor Project Assignment Czech Technical University in Prague Faculty of Electrical Engineering Department of Control Engineering BACHELOR PROJECT ASSIGNMENT Student Martin Vajnar Study programme Cybernetics and Robotics Specialisation Systems and Control Title of Bachelor Project ORTE communication middleware for Android OS Guidelines 1 Get familiar with the ORTE middleware developed at the Department that implements the Real Time Publish Subscribe RTPS protocol Get Familiar with ORTE s use in the control system of mobile robots 2 Port ORTE to mobile device built on Android Operating System 3 Develop an application for mobile phones that will allow to monitor and control robots by a mobile phone 4 Analyze differences between current implementation of ORTE and newer versions of the RTPS standard Propose changes necessary for ORTE to be compatible with the RTPS standard 5 Test and document everything thoroughly Bibliography Sources 1 Object Management Group The real time publish subscribe wire protoco
23. he last cached packet is received the device enters the PSP mode again I found out that the PSP mode affects packet delay as well as packet delay variation This is of particular importance in case of data being sent by ORTE at higher frequencies Android allows a program to switch to Continuously Aware Mode CAM by acquiring WifiLock in the WIFI MODE FULL HIGH PERF mode that is available since Android 3 1 x After an application acquires this lock the Wi Fi module will be kept in CAM even when the device enters sleep mode I measured the ping responses with the WifiLock both acquired and released I used 1 000 packets sent at the interval of 200 milliseconds The results can be seen in Table 8 1 WifiLock taken Yes No Packet loss 0 9 0 2 Min RTT ms 1 2 1 9 Avg RTT ms 3 3 59 6 Max RTT ms 177 2 351 7 Table 3 1 Comparison of Wi Fi ping latencies with and without WifiLock Furthermore the PSP mode could cause issues with some Wi Fi Access Points that do not support it According to 5 this could lead to Wi Fi connection being lost ORTE can be configured to use a multicast communication mode Android by default ignores the incoming multicast traffic for power saving reasons In order to receive it the program has to acquire the MulticastLock Both mentioned locks reguire specific Android permission see Section 3 1 to be granted to an application using them Specifically the WifiLock reguires the WAKE LOCK pe
24. id s start is up To activate the electromagnet that is located at the end of the crane s arm press the Magnet see Figure 5 9 button in the menu Current status of magnet is represented by a check box next to it s entry in the menu If the magnet is enabled the box will be checked and vice versa Voltages Figure 5 10 RoboDruid s Voltage Monitor It is possible to monitor current voltage on different branches used inside the robot as well as it s battery voltage To do that tap on Voltage monitor in the menu a dialog showing the voltages will pop up see Figure 5 10 The displayed values are continuously updated F l 15 09 Set fellow managers 10 1 1 1 192 168 1 5 Own IP Address 192 168 1 20 Network SSID WfQo175dg81 Cancel OK Figure 5 11 RoboDruid s Managers Dialog 22 5 3 User Manual It is possible to enter IP addresses of other computers connected to the robot s Wi Fi AP This could be useful for example to receive current speed of robot that is being controlled by an application launched on the computer on the Android device To do this select the Fellow managers option in menu Next a dialog will pop up see Figure 5 11 IP addresses of neighboring computers could be entered into the text box and separated by a colon By default only the IP address of the Main Controller Board 10 1 1 1 is entered The dialog also displays current IP address associated with the Wi Fi interface
25. kage ready for deploying onto an Android device One possibility to install the application directly onto the device is to connect the device to PC s USB port and use the ADB application from the SDK to do the installation adb install bin RoboDruid debug apk After the installation begins it is necessary to confirm application s permissions on the Android device s screen t Available from webupd8team java ppa repository could be added to local repositories by issuing com mand sudo add apt repository ppa webupd8team java 2 Available from http developer android com tools sdk ndk index html 3 Available from http developer android com sdk index html 20 EOS Near WWaniral 3 3 User IVianual E 5 3 2 User Instructions Power up the robot by flipping the power button and wait for it to finish initialization indicators of function of individual components on the robot s display will turn green In order to connect to the robot s Wi Fi interface you have to first setup a connection profile for the robot s Access Point Open Settings dialog on the Android device tap on Wi Fi and select CTU demo AP and enter demorobot as a passphrase then save the profile and connect to it When the connection is established you can start RoboDruid To do that tap on it s icon in the device s menu After the application s start up the screen on Figure will appear RoboDruid Figure 5 8 RoboDruid s default scr
26. l DDS interoperability wire protocol specification DDS RTPS Online http www omg org spec DDS RTPS 2 1 Nov 2010 2 P Smolik and P P a ORTE The Open Real Time Ethernet Czech Technical University in Prague Tech Rep 2008 Online http orte sf net rtnO8_orte pdf Bachelor Project Supervisor Ing Michal Sojka Ph D Valid until the summer semester 2014 2015 LS signature illegible signature illegible prof Ing Michael ebek DrSc prof Ing Pavel Ripka CSc Head of Department Dean Prague January 30 2014 Prohl en Prohla uji e jsem p edlo enou pr ci vypracoval samostatn a e jsem uvedl ve ker pou it informa n zdroje v souladu s Metodick m pokynem o dodr ov n etick ch princip p i p prav vysoko kolsk ch z v re n ch prac Acknowledgement First I would like to thank my super visor Ing Michal Sojka Ph D for his patience useful advices and guidance Next I would like to thank Ing Pavel Pisa Ph D for his notes on several im plementation problems I have faced My thanks also goes to all former and present members of the Flamingos robotic team at the Faculty of Elec trical Engineering Czech Technical University in Prague Last but not least I would like to thank my parents for supporting me in my studies Abstrakt Real Time Publish Subscribe je pro tokol ktery umoznuje snadnou a efek tivn implementaci datov zen ch distribuo
27. med measurements the drop in throughput is significant A better way to call Java s receive callback function would be to create a dedicated Java thread reading from a custom message queue to which messages could be written directly from the native receive callback function without the need to attach to the Java VM This is considered for future development 14 Chapter 5 Demo application In order to demonstrate functionality of the ported ORTE library I wrote an application in Java for remote control of a small robot The application is called RoboDruid It is capable of displaying information received from an on board Laser Range Finder mon itoring battery voltage and controlling robot s motion Robot s hardware and software is described in Section 5 1 Robot s motion is controlled by an accelerometer embedded in the Android device To suppress the noise accelerometer output is filtered by a low pass filter We use standard sensor API of Android in order to interface with the accelerometer Section expands on the implementation of the demo application Section provides a user manual for the developed application B 51 Demo Robot This section introduces basics of ORTE s use in the robot Detailed description of the robot s hardware and software can be found in 17 and in the diploma thesis of Ing Michal Vok 19 Here we will only describe parts of the robot that are vital for understanding how the different compon
28. nected to it through the CAN bus This application receives CAN mes sages with specific IDs and publishes them as ORTE issues The cand also works in the opposite direction It subscribes to certain ORTE topics and assembles CAN frames from them In other words it serves as a bridge between ORTE and CAN a hokuyod acquires data from LRF and publishes them on ORTE a ortemanager maintains record of ORTE participants across the network E 5 1 3 Mapping of CAN Message IDs to ORTE Topics In this section we take a look at various ORTE Topics used in the robot that are of importance for the development of RoboDruid We also map ORTE Topics to corre sponding CAN Message IDs in Figure 5 1 The description of ORTE Topics uses ORTE IDL language It s syntax is similar to that of the C language ORTE Topic CAN Message alias CAN Message ID motion speed CAN MOTION CMD 0x21 pwr voltage CAN PWR ADC1 CAN PWR ADC1 0x41 0x42 crane cmd CAN CRANE CMD 0x34 magnet cmd CAN MAGNET CMD 0x35 Table 5 1 Mapping of CAN Message IDs to ORTE Topics 16 S E S B BH H E B H H BH B BH H M BH B H H EH B H NH EH B EH BN UH BN B 8 H S EH B 5 Uu 5 3 5 D 2 Implementation Figure 5 1 IDL code for topic motion speed Figure 5 2 IDL code for topic pwr voltage Figure 5 3 IDL code for topic hokuyo scan Figure 5 4 IDL code for topic magnet cmd Figure 5 5 IDL code for topic crane cmd E 5 2 Implementation In this section we describe some impo
29. net ORTE communication middleware to Android Operating System and then use it to develop an application for mobile devices that will be capable of monitoring and controlling a mobile robot The application will use Java wrapper of the ported ORTE library This thesis is structured as follows Chapter p describes the ORTE and the concepts and protocol that it implements Chapter 3 focuses at the process of porting ORTE to Android It provides overview of problems faced during the porting Chapter 4 provides performance analysis of the ported ORTE library as well as an example of use of the Java wrapper of the ported ORTE library Chapter B describes the developed application for controlling a mobile robot It also provides basic information about the robot in question Chapter 2 DDS RTPS and ORTE The popularity of DCPS model resulted in several standardization activities Data Distribution Service DDS for Real time Systems 7 is an Object Management Group OMG standard that specifies an API for applications based on the DCPS model Applications using this API are portable between different middleware platforms of fering this API The interfaces are specified in OMG Interface Definition Language IDL 3 Chapter 7 This means that the API is defined for many commonly used languages such as C C Python and others The DDS API allows an application to declare that it produces certain data identified with a so called topic
30. ocols RTPS V1 0 uses a special application called Manager that runs on every node and manages automatic discovery of applications both on the same node and on remote nodes The VAR submessage is used for exchange of information about QoS parameters topic s type and name etc For more details see 14 Sec tion 5 1 RTPS V2 1 replaces this with the Simple Participant Discovery Protocol and the Simple Endpoint Discovery Protocol that do not need the manager According to 9 Section 8 5 3 3 1 Section 8 5 3 3 2 the SPDP protocol uses data with key and the Stateless implementation of Reader and Writer In line QoS RTPS V2 1 makes it possible to include QoS parameters directly in each Data submessage As per 9 Section 8 7 1 the in line QoS is used in case a Reader does not keep a list of matching remote Writers or the QoS parameters they were configured with This is the case for StatelessReader Removal of VAR submessage The VAR submessage is removed from the RTPS V2 1 as it is now obsolete due to the introduction of the SEDP and in line QoS Chapter 3 Porting to Android Android is one of the most popular and proliferated mobile operating systems It is running on wide variety of devices ranging from mobile phones and tablets to home me dia centers and digital cameras This makes it interesting for soft real time application developers To develop applications for Android Google offers Android Software Develo
31. ower Save Polling PWM Pulse width Modulation QoS Quality of Service RIPS Real Time Publish Subscribe SDK Software Development Kit SEDP Simple Endpoint Discovery Protocol SPDP Simple Participant Discovery Protocol SSH Secure Shell 27 A Abbreviations SSID Service Set Identifier TAO The ACE ORB UDP User Datagram Protocol USB Universal Serial Bus VM Virtual Machine 28 Appendix B Contents of the Attached CD a doc a thesis pdf electronic version of this thesis application RoboDruid apk installation package of the developed RoboDruid application 29
32. pment Kit SDK and Android Native Development Kit NDK SDK is used for applica tions written in Java whereas NDK allows to use native C C code in applications Android uses Google s implementation of Java Virtual Machine JVM called Dalvik VM Having an RTPS implementation running on Android brings interesting possibilities of using Android devices to control and or monitor applications that already use RTPS protocol This was in fact the primary motivation for the porting effort The Flamin gos robotic team has built two mobile robots 17 that use RTPS and a desire to be able to control the robots via a mobile phone was expressed One such robot is depicted in Figure 3 1 In this Chapter we look at Android s permission model in Section BI We provide an overview of the porting process in Section and describe some technical details of the porting in Section B 3 Figure 3 1 Controlling the robot with an Android phone 3 1 Android Permission Model p 3 1 Android Permission Model In this section we will discuss Android s security basics that needed to be taken into account during the ORTE porting and later during development of the robot monitoring and control application Android uses a permission based security model Every application is assigned a unique Linux user ID at the time of installation During the installation process the application s manifest is analyzed for permissions that the application declares as r
33. rability Wire Protocol Specification Current version of this specification is V2 1 9 referred to as RTPS V2 1 The changes from RTPS V1 0 to V2 1 are the subject of this section We will demon strate them on the current state of ORTE implementation We describe the changes needed for ORTE to be compatible with the RTPS V2 1 E 2 1 1 Mapping of objects in ORTE to the RTPS V2 1 Many objects used in ORTE were renamed in the RTPS V2 1 In order to make it easier to track changes in the new standard we make a table 2 1 that maps old names of objects used in ORTE to names of similar objects in RTPS V2 1 For the purpose of Section we define a few terms These definitions reflect the fact that ORTE has it s own API instead of the DDS one By a Participant we mean a communication node on a network that contains Publishers and Subscribers This could be any application running on any node in the network For our needs the word Publisher will be equivalent to a Writer and Subscriber to a Reader Writers and Readers are collectively called Endpoints For detailed description of RTPS structure see 9 Section 7 4 1 1 http www theaceorb com product aboutace html 2 http www theaceorb com 2 1 Compatibility of ORTE with the Latest RTPS standard Name in ORTE Name in the RTPS V2 1 Related Sections in the RTPS V2 1 CSTReader Stateful Reader 8 2 8 description 8 4 10 implementation CSTRemoteWriter WriterProxy 8 4 10 4
34. rmission and the MulticastLock reguires the CHANGE WIFI MULTICAST STATE per mission E 3 3 5 Java Manager A Java version of the native ORTE Manager was created to overcome problems with execution and termination of native processes For the role of the Manager see Sec tion p 13 The Java version was created by adding a wrapper around the ORTE functions used by the native Manager The only functionality required on the Android is the possibility for the Java Manager to see other communication nodes on the network That is why the only currently implemented feature of the native Manager is the possibility to pass an option specifying IP addresses of nodes to the underlying ORTE functions However Manager s wrapper could be easily extended to pass another options to ORT E functions 10 Chapter 4 Evaluation The ported ORTE Java wrapper was evaluated by writing a simple application Sec tion 4 1 and comparing the performance of the native and Java implementations Sec tion 4 2 p 4 1 Example Android Application Figures and 4 4 show code of a simple publisher and subscriber First an application creates a DomainApp object then registers the data type see Figure 4 2 that it uses and finally registers a publisher or subscriber Publisher can publish new data by calling the send method Subscriber receives data in the callback method In order for applications to find each other a manager application see Figure 4 1 is need
35. rsity in Prague 2008 Online http orte sf net rtn08 orte pdf visited 5 2014 16 Michal Sojka ORTE web site Online http orte sf net visited 5 2014 17 Kh Tran Duy M Zidek J Benda J Kubias and M Sojka Autonomous Robot Running Linux for the Eurobot 2007 Competition In Ninth Real Time Linux Workshop Real Time Linux Foundation 2007 18 Martin Vajnar Michal Sojka and Pavel P a Porting of Real Time Publish Subscribe Middleware to Android In Fifteenth Real Time Linux Workshop Real Time Linux Foundation 2013 19 Michal Vok Demonstra n robotick platforma Master s thesis Fakulta elek trotechnick CVUT 2012 26 Appendix A Abbreviations ACE Adaptive Communication Environment ADB Android Debug Bridge ADT Android Development Tools AP Access Point API Application Programming Interface BLDC Brushless Direct Current electric motor CAM Continuously Aware Mode sometimes also called Constantly Awake Mode CAN Controller Area Network CORBA Common Object Request Broker Architecture CPU Central Processing Unit DCPS Data centric publish subscribe DDS Data Distribution Service GUI Graphical User Interface IDL Interface Description Language IP Internet Protocol JNI Java Native Interface JVM Java Virtual Machine LRF Laser Range Finder MCB Main Controller Board NDK Native Development Kit OMG Object Management Group ORTE Open Real Time Ethernet OS Operating System PC Personal Computer PSP P
36. rtant aspects of implementation of the Robo Druid Section 5 2 1 gives a basic overview of the application s package structure In Section we describe how the data from accelerometer are acguired and used for robot s motion control In Section we look on how the data received from robot s Laser Range Finder are processed and drawn B For complete source code of the application see http rtime felk cvut cz gitweb orte git tree HEAD orte contrib Robot Demo 17 5 Demo application E 5 2 1 Java Package Structure The application is structured into four separate Java packages The first one is called GUI and consists of classes dealing with the main Activity s creation and custom View that handles the drawing of actual speed vector of the robot and visualiza tion of received data from the Laser Range Finder onboard the robot The second one called DataTypes includes classes extending MessageData that describe the data types for given topics sent through ORTE The third called Publishers and fourth called Subscribers define publishers and subscribers of different topics used in the application E 5 2 2 Acquisition and Processing of Accelerometer data Many today s Android devices are equipped with a 3 axis accelerometer that is used mainly in games and for changing screen orienation based on current direction of the acceleration vector We use the accelerometer in order to control the angular and linear v
37. source needs Simple implementations can have small memory footprint but will need higher network bandwidth Other implementation can use abundance of local memory to highly optimize the communication and thus save network bandwidth The RTPS protocol has the following features that make it an interesting option for distributed real time applications a No single point of failure Every application has a complete model of the whole network Crash of a single application influences only the applications that need data from it However this holds only in trusted networks either local or VPN On public networks data sent through RTPS could be tampered with The attacker could pretend to be a legitimate node and inject arbitrary data into the network that would be delivered to subscribers of specific topic 1 See http www omg org spec Ma p g org sp p 2 DDS RTPS and ORTE Redundancy Multiple publishers can publish the same topic If one publisher fails subscribers will be automatically switched to another one This is illustrated in Figure where Presure information is published by two applications Application discovery Built in discovery protocol ensures that applications can dis cover each other as well as the topics they publish or are subscribed to Besides several commercial implementations of the RTPS protocol at least two open source implementations exist OpenDDS 10 and ORTE 16 OpenDDS appears
38. tached to the VM it uses the system class loader for FindClass calls The system class loader does not see ORTE Java classes To overcome this we use the JNI OnLoad function Any FindClass calls made from there will happen in the context of the class loader of class that initiated the process of loading the shared library The JNI OnLoad function is called by the VM during this loading process We take the class loader object of class org ocera orte JOrte and make it a global reference inside the VM by calling NewGlobalRef Then we store the created reference in a static global variable This is to make it accessible for later class look ups To perform a class look up using the stored class loader object we need to pass the name of the requested class to it s findClass method We do this by means of the JNI function CallO0bjectMethod which takes as a parameter the method ID of the findClass method To speed up future look ups we use the fact that the stored class loader has been turned into a global reference so we need to get the required method ID only once because it will remain the same We get the method ID inside the JNI_OnLoad function and store it in a static global variable The class loader object stores references to already looked up classes and requires the user to invoke method findLoadedClass during subsequent look ups of such classes To simplify the described class loading process inside the JNI code I wro
39. te a C func tion that first invokes the findLoadedClass method and if unsuccessful the requested class was not yet looked up invokes the findClass method E 3 32 Direct ByteBuffer In this section we first describe the Java ByteBuffer class then we elaborate on why it is used in ORTE Next we describe how it was previously used in the Java wrapper and what problems that caused Last we take a look at adopted solution According to ByteBuffer provides get and put methods that read and write values of primitive data types translating them to and from sequences of bytes in a particular byte order By default Big Endian is used There are two types of Byte Buffers direct and non direct that differ in the way the VM performs I O operations upon them For implementation see http rtime felk cvut cz gitweb orte git commit b2b73b5c892eb04fc4822340fe9fef3bb99d4e31 3 3 Technical Details During the process of sending receiving new data through ORTE the data first need to be serialized deserialized We use java nio ByteBuffer to accomplish this in the Java wrapper Upon new data s arrival a C callback function is called by ORTE The role of this callback is to hand over the data to Java Previously the received data were copied from an internal ORTE buffer to a non direct ByteBuffer while the byte order of the received data was ignored and was assumed to always be Big Endian This caused data received from hosts that use Li
40. tion for them Traditional middleware platforms such as CORBA 8 provide transparent access to remote objects by means of remote method calls When an application invokes a method on a remote object the middleware automatically serializes the method parameters and sends the request to destination process where the object is located The computation happens remotely and then the results are sent back While this simplifies the devel opment of distributed applications a lot there are many applications that cannot be efficiently implemented on top of this request response model Figure 1 1 Data Centric Publish Subscribe application model Applications whose operation is mainly data driven meaning that some ac tion computation is performed when data is ready would be better served by middleware platforms that seamlessly manage distribution of data from producers to consumers Such applications are often designed according to Data Centric Publish Subscribe DCPS model 7 where the middleware creates a notion of a global data space that is accessible to all interested applications see Figure 1 1 Writing applica tion under such a model brings many advantages The biggest one being perhaps that 1 Introduction the communication requirements are specified by applications in a declarative way and the middleware handles the data exchange automatically based on the declarations The aim of this thesis is to port Open Real Time Ether
41. to be more mature It implements both the DDS API and the underlying RTPS protocol It is implemented in C and provides bindings for Java OpenDDS is built on top of the ACE abstraction layer to provide platform portability OpenDDS also leverages capabilities of CORBA implementation called TAO ORTE another open source RTPS implementation provides its own API instead of the DDS API The reason is that ORTE development started before the DDS standard was finished ORTE is implemented in C and includes a small portability layer that allows it to run on many popular platforms including Linux Windows MacOS and FreeBSD Unfortunately ORTE implements the RTPS protocol according to the draft of the RTPS specification and it would need some changes see Section 2 1 in order to be compliant with the current specification The ORTE library was originally created by Ing Petr Smolik and Ing Pavel Pisa Ph D 15 and it s Java wrapper was originally created by Ing Luk Pokorny 13 B 21 Compatibility of ORTE with the Latest RTPS standard ORTE is one of the first implementations of the RTPS protocol In fact it was a proof of concept implementation intended for testing of completeness and self consistency of the RTPS specification RTPS is standardized by the OMG as the RTPS Wire Protocol ORTE was imple mented using referred to as RTPS V1 0 The RTPS standard was later renamed to The RTPS Wire Protocol DDS Interope
42. ttle Endian byte order to be unreadable The sending of data was handled analogously to their reception so we will not describe it Now a direct ByteBuffer is used This made it possible to merge the internal ORTE buffer with the ByteBuffer They both now share the same memory region to store elements and it is no more necessary to copy data between the C and Java buffers This reduced the overhead of sending receiving data Further when new data are received by ORTE and the C callback function is called a byte order of the used ByteBuffer is set in accordance with the received data For more information about the receive callback function see Section 4 2 Though it seems that the direct ByteBuffer is an excellent solution to mentioned strugles there is one limitation The JNI standard defines that the function needed to access direct ByteBuffer is optional to implement see 12 Function GetDirect BufferAddress Fortunately many major implementations including Oracle s VM OpenJDK and Dalvik choose to implement it because it is used in cooperation with OpenGL for graphics drawing However some exotic implementations need not imple ment it and the Java wrapper will not work with them B 3 3 3 64 bit Support In the Java wrapper pointers to C structures are stored in Java fields for later use For example each publisher is assigned an instance of ORTEPublication structure upon its creation for future manipulation the most important
43. turn ORTEConstant SHORT FIELD SIZE m Jj Figure 4 2 Code of a simple Java Data type class performance of the underlying network I measured how long does it take to publish ten thousand integer values The experiments were run on three different devices Sony Ericsson Xperia Ray with Android 4 0 4 Google Nexus 7 with Android 4 3 and a PC with Intel Core i7 3520M CPU running at 2 90 GHz with OpenJDK 7 The results can be seen in Table 4 1 Pub Sub Xperia Nexus 7 PC C gt C DDS 238 0 31 s Java Java 10 3 s 6 8 s 0 78 s C Java 10 1 s 6 3 s 0 78 s Java C 2 6 s DIDES 0 31 s Table 4 1 Performance comparison of native code and Java wrapper Time needed for publication of 10 000 integer values The relative slowdown of the Java implementation compared to the native one is depicted in Figure 4 5 It can be seen that Dalvik VM performance has improved between version 4 0 4 and 4 3 or that it runs better on Nexus 7 hardware OpenJDK performs even better than Dalvik VM There is no slowdown in Java C case and in both cases with the subscriber in Java the performance is the same 12 4 2 Performance Comparison import org ocera orte import org ocera orte types public class ExamplePublisher public static void main String args throws Exception NtpTime persistence new NtpTime 3 int strength 100 DomainApp appDomain new DomainApp 0 DomainProp defaultPropsCreate null fals
44. van ch aplikac pracuj c ch v re ln m ase Protokol byl p ijat jako standard Object Management Group OMG a je ur en k zaji t n spolupr ce aplikac postaven ch na Data Distribution Service DDS API RTPS je vyu v n v mnoha pr myslov ch aplikac ch a existuj jak ko mer n tak svobodn implementace Jedna ze svobodn ch implementac se naz v Open Real Time Ethernet ORTE a funguje na ad platforem Nap GNU Linux Windows FreeBSD a MacOS V t to pr ci popisuji nov p r stek k podporovan m platform m kter m je opera n syst m Android pro mobiln za zen Tato pr ce uv d p ehled krok kter byly nutn k portov n na plat formu Android Portoval jsem existuj c nativn knihovnu a Java wrapper Po p eme probl my na kter jsem narazil a jejich e en Porovn me v kon ORTE na Androidu s dal mi platformami a p edstav me aplikaci k ovl d n a mo nitorov n mobiln ho robotu pro tele fony s Androidem Kl ov slova DCPS DDS RTPS ORTE OS Android Java Native Inter face komunikace v re ln m ase P eklad titulu Komunika n middle ware ORTE pro OS Android Abstract Real Time Publish Subscribe is a protocol that allows easy and eff cient implementation of data driven distributed real time applications The protocol was adopted as an Object Man agement Group OMG specification and it is intended as an interoperability
Download Pdf Manuals
Related Search