porting implementation of packet utilization standard from ada to java annelie hultman (tec-eme)...

Porting Implementation of Packet Utilization Standard

from ADA to JAVA

Annelie Hultman (TEC-EME)Donata Pedrazzani (TEC-EMS)

ESA/ESTEC 2004

JPUS de-briefing

05/05/2004May 04 ESA/ESTEC - JPUS de-briefing 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


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


Outline• Architecture issuesArchitecture issues

- Ada packages versus Java OOAda packages versus Java OO

- Encapsulation of data/visibilityEncapsulation of data/visibility

- Reusability conceptsReusability concepts

- PolymorphismPolymorphism

• Low-level Low-level operationsoperations• Porting strategiesPorting strategies

- Porting of typesPorting of types

- Porting of Ada generic packagePorting of Ada generic package

- Porting of protected objects and protected entriesPorting of protected objects and protected entries

- ConclusionConclusion


Ada packages vs Java OO

Ada

Unit of encapsulation: package

Java

Unit of encapsulation: classPackage: repository for classes, host-environment

facility which contains compiled class files


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 bodyAccess control modifiers


Encapsulation of data/visibility(2)

A B C DAccessible by c2 yes -Accessible by c3 -Accessible by c4 - -Accessible by c5 - - -

class c1 {public int A;

protected int B;int C;

private int D;}

class c3 {...

}

class c5 {...

}

class c4 extends c1 {...

}

class c2 extends c1 {...

}

yesyesyes

yesyesyes

yesyes


Reusability concepts

Ada

Specification and compiled units

Java

javadoc documentation and bytecode (compiled .class files)


Polymorphism

Def: ability for references and collections to hold objects of different types

AdaExplicit: use of tagged types

JavaImplicit from the language


Polymorphism in Java

PUSPacket

TMPacketTCPacket



- Ada packages versus Java OOAda packages versus Java OO- Encapsulation of data/visibilityEncapsulation of data/visibility- Reusability conceptsReusability concepts- PolymorphismPolymorphism


- Porting of typesPorting of types- Porting of Ada generic packagePorting of Ada generic package- Porting of protected objects and protected entriesPorting of protected objects and protected entries

• ConclusionConclusion


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




• Low-level Low-level operationsoperations

• Porting strategiesPorting strategies- Porting of types- Porting of Ada generic package- Porting of protected objects and protected entries



Porting Strategies

• Porting of types• Porting of Ada generic package• Porting of protected objects and protected entries


Porting of Types

• New scalar types • Enumeration types• Arrays• Heterogeneous data structures (records)


Porting of Types Arrays and Records

• ArraysAn 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.


Porting of Types Example Arrays and Records (1)

subtype Command_Index is Natural range 1 .. Schedule_Size;

type Command_Schedule is array (Command_Index) of Optional_Command_Schedule_Info;



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;



type Command_Schedule_Info isrecord

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;



1

*

packet : TCPacket


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


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.


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.


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…

}


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


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)of PUS_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];


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





- Porting of typesPorting of types- Porting of Ada generic packagePorting of Ada generic package- Porting of protected objects and protected entriesPorting of protected objects and protected entries



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


Future work

• Java– Full implementation of the services– Port to Hard Real Time Java (Aero/jamaica)– Assess the architectural performances– Testing

porting implementation of packet utilization standard from ada to java annelie hultman (tec-eme)...

Documents

external packet header

packet header field

pus ada framework

length i outi

units specification

public synchronized

ygt periodported

hostenvironment facility