Porting Implementation of Packet Utilization Standard from ADA to JAVA

1. Porting Implementation of Packet Utilization Standard from ADA to JAVA JPUS de-briefing Annelie Hultman (TEC-EME) Donata Pedrazzani (TEC-EMS) ESA/ESTEC 2004

2. Introduction • Final presentation of the YGT period • Ported part of the PUS Ada framework to Java • Aim of presentation • De-briefing of key findings which may be interesting for the sections ESA/ESTEC - JPUS de-briefing

3. Outline • Architecture issues • Ada packages versus Java OO • Encapsulation of data/visibility • Reusability concepts • Polymorphism • Low-level operations • Porting strategies • Porting of types • Porting of Ada generic package • Porting of protected objects and protected entries • Conclusion ESA/ESTEC - JPUS de-briefing

4. Outline • Architecture issues • Ada packages versus Java OO • Encapsulation of data/visibility • Reusability concepts • Polymorphism • Low-level operations • Porting strategies • Porting of types • Porting of Ada generic package • Porting of protected objects and protected entries • Conclusion ESA/ESTEC - JPUS de-briefing

5. Ada packages vs Java OO Ada • Unit of encapsulation: package Java • Unit of encapsulation: class • Package: repository for classes, host-environment facility which contains compiled class files ESA/ESTEC - JPUS de-briefing

6. Encapsulation of data/visibility Ada • Physical separation between unit’s specification and body • Accessibility given by location of declaration Java • No separation of a class into specification and body • Access control modifiers ESA/ESTEC - JPUS de-briefing

7. Encapsulation of data/visibility(2) ESA/ESTEC - JPUS de-briefing

8. Reusability concepts Ada • Specification and compiled units Java • javadoc documentation and bytecode (compiled .class files) ESA/ESTEC - JPUS de-briefing

9. Polymorphism Def: ability for references and collections to hold objects of different types Ada • Explicit: use of tagged types Java • Implicit from the language ESA/ESTEC - JPUS de-briefing

10. Polymorphism in Java ESA/ESTEC - JPUS de-briefing

11. Outline • Architecture issues • Ada packages versus Java OO • Encapsulation of data/visibility • Reusability concepts • Polymorphism • Low-level operations • Porting strategies • Porting of types • Porting of Ada generic package • Porting of protected objects and protected entries • Conclusion ESA/ESTEC - JPUS de-briefing

12. Low-level operations • Java cannot directly control hardware: programs must declare native methods (i.e. using JNI) and implement such operations in another language • Encoding/decoding to communication link in the framework ESA/ESTEC - JPUS de-briefing

13. Outline • Architecture issues • Ada packages versus Java OO • Encapsulation of data/visibility • Reusability concepts • Polymorphism • Low-level operations • Porting strategies • Porting of types • Porting of Ada generic package • Porting of protected objects and protected entries • Conclusion ESA/ESTEC - JPUS de-briefing

14. Porting Strategies • Porting of types • Porting of Ada generic package • Porting of protected objects and protected entries ESA/ESTEC - JPUS de-briefing

15. Porting of Types • New scalar types • Enumeration types • Arrays • Heterogeneous data structures (records) ESA/ESTEC - JPUS de-briefing

16. Porting of TypesArrays and Records • Arrays An array is in Java encapsulated in a class together with the operations on the array. This solution is not strictly necessary to carry out the porting, but it is more object oriented. • Heterogeneous data structures (records) A record in Ada is replaced by a class in Java. The operations on the variables of the record type in Ada are in Java implemented inside the class.  ESA/ESTEC - JPUS de-briefing

17. Porting of TypesExample Arrays and Records (1) subtype Command_Index is Natural range 1 .. Schedule_Size; type Command_Schedule is array (Command_Index) ofOptional_Command_Schedule_Info; ESA/ESTEC - JPUS de-briefing

18. Porting of TypesExample Arrays and Records (2) type Optional_Command_Schedule_Info(Void : Boolean := True) is record case Void is when True => null; when False => Cmd_Schedule_Info : Command_Schedule_Info; end case; end record; ESA/ESTEC - JPUS de-briefing

19. Porting of TypesExample Arrays and Records (3) type Command_Schedule_Info is record TC_Packet : PUS.PUS_Packet; Sub_Schedule_ID_Inf : Sub_Schedule_ID; Scheduling_Event_Spec_Inf : Scheduling_Event_Spec; Time_Tag : On_Board_Scheduling_Types.CUC_Time; Actual_Schedule_Time : Optional_On_Board_Time; end record; ESA/ESTEC - JPUS de-briefing

20. 1 * packet : TCPacket Porting of TypesExample Arrays and Records (4) ESA/ESTEC - JPUS de-briefing

21. Porting of Ada generic package An Ada generic package is a template, which can be parameterized, and from which corresponding nongeneric packages (instances) can be obtained. In Java a class serves as a template for creating objects (instances). • Generic Subprogram Parameters • Generic Value Parameters • Generic Type Parameters ESA/ESTEC - JPUS de-briefing

22. Generic Subprogram Parameters • Ada: The implementation of the actual subprogram is given at the instantiation of the generic package. • Java: The generic Ada package is ported to an Java abstract class. The actual subprogram is implemented in the subclass inheriting from the abstract class. ESA/ESTEC - JPUS de-briefing

23. Generic Value Parameters • Ada: generic value parameters are used for passing values or variables to a generic package • Java: passing the parameters via the constructor. ESA/ESTEC - JPUS de-briefing

24. Generic Value ParametersExample Public class CommandSchedule { // Attributes private CommandScheduleInfo [] cmdSchedule; private final int schSize; //Constructor. public CommandSchedule(int scheduleSize){ schSize = scheduleSize; cmdSchedule = new CommandScheduleInfo[schSize]; } // Methods… } ESA/ESTEC - JPUS de-briefing

25. Generic Type Parameters • Discrete types • Ada: Which discrete type is defined at the instantiation • Java: Integer • Private types • Ada: Any type where assignment and comparison is allowed • Java: PUSPacket class, or more general, Object class ESA/ESTEC - JPUS de-briefing

26. Generic Type ParametersExample Discrete Types type Sub_Schedule_ID is (< >). The range of the type is used for indexation of arrays. type Sub_Schedule_Times_Type is array (Sub_Schedule_ID)ofPUS_Data_Types.On_Board_Time; Sub_Schedule_Times : Sub_Schedule_Times_Type; In Java: integer type. The array indexation is made by having the number of sub schedules as a constant in e.g. the class MissionParameters.java. private int[] subScheduleTimes = new int[MissionParameters.NUMBER_OF_SUBSCHEDULES];  ESA/ESTEC - JPUS de-briefing

27. Porting of Protected objects and Protected entries • Protected objects in Ada are implemented in Java by using synchronized methods. • Protected entries in Ada are implemented in Java by using the wait/notify construction in Java ESA/ESTEC - JPUS de-briefing

28. Outline • Architecture issues • Ada packages versus Java OO • Encapsulation of data/visibility • Reusability concepts • Polymorphism • Low-level operations • Porting strategies • Porting of types • Porting of Ada generic package • Porting of protected objects and protected entries • Conclusion ESA/ESTEC - JPUS de-briefing

29. Conclusion Porting: • need of a model to understand the Ada code (i.e.:UML) • need of a well-defined porting strategy: • Ada 83 procedural language • Ada 95 has some object-based features • Java object oriented language Some issues to address: • direct communication with the hardware • how to represent low level data types with Java ESA/ESTEC - JPUS de-briefing

30. Future work • Java • Full implementation of the services • Port to Hard Real Time Java (Aero/jamaica) • Assess the architectural performances • Testing ESA/ESTEC - JPUS de-briefing