Difference between pages "Tasking Event-B Overview" and "Tasking Event-B Tutorial"

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=== Tasking Event-B ===
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THIS PAGE IS UNDER CONSTRUCTION !!!!!!
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Tasking Event-B can be viewed as an extension of the existing Event-B language. We use the existing approaches of refinement and decomposition to structure a project that is suitable for a Tasking Development. During the modelling phase parameters are introduced to facilitate decomposition. As a result of the decomposition process, parameters become part of the interface that enables event synchronization. We make use of this interface and add information (see [[#Implementing Events]]) to facilitate code generation. The tasking extension consists of the constructs in the following table.
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 +
For more information contact Andy Edmunds - University of Southampton - mailto:ae2@ecs.soton.ac.uk
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=== Tasking Event-B Tutorial Overview ===
 +
 
 +
This code generation tutorial supplements the Heating Controller tutorial example, and makes use of example projects from the download site. The code generation stage produces implementable Ada code, and also an Event-B project which models the implementation. The Ada code is produced using a pretty printer tool from an intermediate model, the Common Language model (IL1), generated by a translation tool. An overview of Tasking Event-B can be found on the [[Tasking_Event-B_Overview]] page.
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 +
The Heating Controller development has been refined to the point where we wish to add implementation constructs. The Event-B language is not expressive enough to fully describe the implementation. Tasking Event-B facilitates this final step to implementation, by extending Event-B with the necessary constructs. Event-B machines that are to be implemented (and their seen Contexts) are selected and added to a ''Tasking Development''; the Tasking Development files have the file extension ''.tasking''. The machines in the Tasking Development are then extended with implementation details.
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 +
The example/tutorial projects are,
  
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<center>
 
 
{| border="1"
 
{| border="1"
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!Construct
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|Heating_ControllerTutorial_Completed
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!Options
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|An example project with a completed Tasking Development and IL1 model (post IL1 translation, but before Event-B translation).
 
|-
 
|-
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|Machine Type
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|Heating_ControllerTutorial_Completed_Gen
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|DeclaredTask, [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines AutoTask], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Shared_Machines SharedMachine], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#The_Environ_Machine Environ]
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|Same as the example project above, but with Event-B model translations. The difference being that this development includes a model of the implementation. These are refinements that include a program counter to describe flow of execution in each task.
 
|-
 
|-
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|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Control_Constructs Control]
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|Heating_ControllerTutorial_Step1
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|Sequence, Loop, Branch, Event, Output
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|A bare project for step 1 of the [[Code_Generation_Tutorial#The_Tutorial |tutorial]].
 
|-
 
|-
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|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines Task Type]
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|Heating_ControllerTutorial_Step2
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|Periodic(n), Triggered, Repeating, OneShot
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|A partially completed tasking development for steps 2, 3 and 4 of the [[Code_Generation_Tutorial#The_Tutorial |tutorial]].
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|-
 
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|Priority
 
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| -
 
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|-
 
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|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Implementing_Events Event Role]
 
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| Actuating, Sensing
 
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|-
 
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|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Addressed_Variables Addressed Variable]
 
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|Address, Base
 
 
|}
 
|}
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</center>
 
  
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==== Tasking Machines ====
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== Preliminaries ==
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The following constructs relate to Tasking and Environ Machines, and provide implementation details. Timing of periodic tasks is not modelled formally. Tasking and Environ Machines model Ada tasks, so they can be implemented easily in Ada; in C using the pthread library, or in Java using threads.
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Before further discussion of the modelling aspects, we take a look at the PrettyPrint viewers. The PrettyPrinters make the viewing of IL1 and tasking models easier; it also provides a route to generate source code. The source code can easily be pasted from the IL1 Pretty Printer window into an the Ada source file .
 +
==== The PrettyPrint View of a Tasking Development ====
 +
To open the Tasking PrettyPrint viewer,
 +
* from the top-menu select ''Window/Show View/Other/Tasking Pretty Printer''.
 +
 
 +
Note that the Tasking PrettyPrinter may have to be closed when editing the Tasking Development, since it can give rise to exceptions. The PrettyPrinter would need further work to make it robust, however it is intended only as a short-term solution.
 +
 
 +
* Open the ''Heating_ControllerTutorial_Completed'' Project and switch to the Resource Perspective.
 +
* Open the ''.tasking'' model and inspect it. Clicking on the Main, Machine or Event nodes updates the pretty print window.
 +
 
 +
==== Viewing Source Code ====
 +
aka. The PrettyPrint View of an IL1 Model.
 +
 
 +
To view Ada source code,
 +
* from the top-menu select ''Window/Show View/Other/IL1 Pretty Printer''.
 +
* Open the ''Heating_ControllerTutorial_Completed'' Project and switch to the Resource Perspective.
 +
* Open the ''.il1'' model and inspect it. Clicking on the Protected, Main Entry, or Task nodes updates the pretty print window.
 +
 
 +
==== Cleaning the Tasking Development ====
 +
If the ''.tasking'' file has errors, then it may need cleaning. To do this right-click on the ''Main'' node, select ''Epsilon Translation/CleanUp''. If a model has errors it can still be viewed by clicking on the ''Selection'' tab at the bottom of the tasking editor window.
  
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* Tasking Machines may be one of the following types:
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== The Tutorial ==
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** AutoTasks - Anonymous Tasks running from start-up.
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The steps needed to generate code from an Event-B model, in this tutorial, are as follows,
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** Declared tasks - (Not currently used) A task template relating to an Ada ''tasktype'' declaration.  
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* Step 1 - [[Tasking Event-B_Tutorial#Creating The Tasking Development|Create the tasking development]].
 +
* Step 2 - [[Tasking Event-B_Tutorial#Providing the Annotations for Implementations|Add Tasking annotations]].
 +
* Step 3 - [[Tasking Event-B_Tutorial#Optional Annotations for Addressed Variables|Add annotations for addressed variables (optional)]].
 +
* Step 4 - [[Tasking Event-B_Tutorial#Invoking the Translation|Invoke translators]].
  
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''Auto Tasks'' are tasks that will be declared and defined in the ''Main'' procedure of the implementation. The effect of this is that the ''Auto Tasks'' are created when the program first loads, and then activated (made ready to run) before the ''Main'' procedure body runs.
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==== Creating The Tasking Development ====
 +
* Change to the Event-B Perspective.
 +
* Open the ''Heating_ControllerTutorial_Step1'' Project.
 +
* Select the following Machines: Display_Update_Task1, Envir1, Heater_Monitor_Task1, Shared_Object1, Temp_Ctrl_Task1 and HC_CONTEXT.
 +
* Right-click and select ''Make Tasking Development/Generate Tasking Development''.
  
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* Tasking and Environ Machines options are:
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The new Tasking Development will not be visible in the Event-B perspective, change to the resource perspective, open and inspect the new ''.tasking'' file. The Tasking Development contains (the EMF representation of) the machines that we wish to provide implementations for. In order to introduce the new concepts we have prepared a partially complete development.  
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** TaskType - Defines the scheduling, cycle and lifetime of a task. i.e. one-shot periodic or triggered. The period of a task is specified in milliseconds.
 
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** Priority - An integer value is supplied, the task with the highest value priority takes precedence when being scheduled. The default priority is 5.
 
  
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==== Shared Machines ====
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Change to the Project ''Heating_ControllerTutorial_Step2'' to begin the next step.
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A Shared Machine models a protected resource, such as a monitor. It may be implemented in Ada as a Protected Object, in C using mutex locking, or in Java as a monitor.
 
  
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* A Shared Machine is identified using the ''Shared Machine'' annotation.
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==== Providing the Annotations for Implementations ====
 +
* Close any Tasking Pretty Print Viewers that remain open. The incomplete model will give rise to exceptions.
 +
* Go to the to the Resource Perspective.
 +
* Open and inspect the ''.tasking'' machine.
  
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==== The Environ Machine ====
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The ''Display_Update_Task1'', ''Envir1'' and ''Shared_Object1'' machines are incomplete. We will take the necessary steps to provide implementation details.  
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An Environ machine is a model of the environment. It can be used to generate code for use in a simulation, or be discarded in the case that a simulated environment is not required.
 
  
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* An Environ Machine is identified using the ''Environ Machine'' annotation.
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===== The Display_Update_Task1 Machine =====
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In the partially complete tutorial project we already identified the ''Display_Update_Task1'' as an ''Auto Task'' Tasking Machine, by adding the ''Auto Task'' extension. ''Auto Tasks'' are tasks that will be declared and defined in the ''Main'' procedure of the implementation. The effect of this is that the ''Auto Tasks'' are created when the program first loads, and then activated (made ready to run) before the ''Main'' procedure body runs. We have added the ''Periodic Task'' extension to the ''Auto Task'', and set a period of 500 milliseconds. We will now complete the sequence that has been partially defined in the task body.
  
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=== Control of Program Flow ===
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TO HERE!!!
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At the implementation stage we need to think about controlling the flow of execution; and where interaction with the environment is concerned, how events should be implemented. The following section describes the constructs that we have introduced to facilitate this.
 
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==== Control Constructs ====
 
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Each Tasking Machine has a ''task body'' which contains the flow control (algorithmic constructs).
 
  
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* We have the following constructs available in the Tasking Machine body:
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*'''Add Synchronisation between DIGet_Target_Temperature1 and SOGet_Target_Temperature1'''.
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** Sequence - for imposing an order on events.
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** Expand the ''Auto Task Machine'' node.
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** Branch - choice between a number of mutually exclusive events.
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** Expand the ''Seq'' sub-tree.
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** Loop - event repetition while it's guard remains true.
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** Right-click on the ''Seq'' node and select ''New Child/Left Branch EventWrapper''.
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** Event - a wrapper for the Event-B element (soon to be redundant).
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** Provide the event label ''d1'' using the properties view.
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** Text Output - writes textual output to the screen.
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** Right-click on Event Wrapper and select ''New Child/ Synch Events''.
 +
** Select ''Synch Events'' and go to the drop-down menu of the ''Local Event'' property.
 +
** At this point the drop-down box displays a number of event names, select the '''second''' ''DIGet_Target_Temperature1'' event.
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** Go to the drop-down menu of the ''Remote Event'' property.
 +
** From the list of events select the '''second''' ''SOGet_Target_Temperature1'' event.
  
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The syntax for task bodies, as used in the Rose TaskBody editor, is as follows:
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The Synch Events construct is used to implement [[Tasking Event-B Overview#Control Constructs|Event Synchronisation]]. The next step wraps an event in an Event Wrapper in order to update the local state; there is no synchronisation as such but we will re-use the constructs that already exist.
  
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<br/>
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*'''Add the Wrapped Event TcalcWVal'''.
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[[Image:Syntax.png]]
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** Expand the sub-tree of the second ''Seq'' node.
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<br/>
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** Right-click on the ''Seq'' node and select ''New Child/Left Branch EventWrapper''.
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** Provide the event label ''w2'' using the properties view.
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** Right-click on Event Wrapper and select ''New Child/ Synch Events''.
 +
** Select ''Synch Events'' and go to the drop-down menu of the ''Local Event'' property.
 +
** From the list of events select the ''TcalcWVal'' event.
  
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The ''String'' will be an event name, a variable name, or a text fragment to be output to the screen. The concrete syntax is shown in bold red font. '*' indicates 0 or more; [] indicates 0 or 1.
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We have now completed the task body, and it just remains to complete provide details for the ''TWrite'' event. The ''TWrite'' event in ''WriterTsk'' is to be synchronized with the ''SWrite'' event in the ''SharedObj''.
 +
*'''Add Event Extensions'''.
 +
** Right-click on the ''TWrite'' Event node.
 +
** Select ''New Child/Extension''.
 +
** Right-click on the ''Extension'' node and select ''New Child/Implementation'' from the menu.
 +
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''ProcedureSynch''.
  
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===== Event Translation =====
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*'''Identify Incoming and Outgoing parameters'''.
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When an event, used in the task body, is translated to an implementation its translation depends on where it is used in the task body. The mappings are relatively simple for branch, loop, and sequence. The Output is not linked to an event, but the Event translation depends on whether it is part of a synchronization: the simplest translation is when no synchronization is involved. The translator checks the composed machine to see if the event is paired in a combined event. If it is not, then the actions of the event are
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** Right-click on the ''outAP'' node and add an ''Extension''.
 +
** Right-click on the ''Extension'' and select''New Child/Parameter Type''.
 +
** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''actualOut''.
 +
** Right-click on the ''inAP'' node and add an ''Extension''.
 +
** Right-click on the ''Extension'' and select''New Child/Parameter Type''.
 +
** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''actualIn''.
  
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===== Synchronization =====
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===== The Shared Machine =====
  
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Synchronization between local events (in AutoTasks) and remote events (in shared/Environ Machines) is determined using the composed machine. To use an event simply enter its name in the TaskBody editor. The translator will in-line any local actions, and add a call to perform remote updates, and obtain remote data.
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The next step is to identify the ''SharedObj'' machine as a ''Shared Machine''. The ''SharedObj'' Machine will be extended using the Event-B EMF extension mechanism.
 +
* Right-click on the ''SharedObj'' Machine node in the ''.tasking'' file.
 +
* Select ''New Child/Extension''.
 +
* Right-click on the ''Extension'' node and select ''New Child/Shared Machine'' from the menu.
  
 +
We now show how to extend the ''SWrite'' event of the Shared Machine with details about its implementation. The ''SWrite'' event in ''SharedObj'' is to be synchronized with the ''TWrite'' event in the ''WriterTsk''.
 +
* '''Identify SWrite as a Syncronisation'''.
 +
** Right-click on the ''SWrite'' Event node.
 +
** Select ''New Child/Extension''.
 +
** Right-click on the ''Extension'' node and select ''New Child/Implementation'' from the menu.
 +
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''ProcedureSynch''.
  
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Synchronization corresponds to:
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* '''Identify incoming and outgoing parameters'''.
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* a subroutine call from task to shared machine, or,
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** Right-click on the ''inFP'' node and add an ''Extension''.
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* sensing or actuating of environment variables.
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** Right-click on the ''Extension'' and select''New Child/Parameter Type''.
 +
** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''formalIn''.
 +
** Right-click on the ''outFP'' node and add an ''Extension''.
 +
** Right-click on the ''Extension'' and select''New Child/Parameter Type''.
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** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''formalOut''.
  
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In the case of a subroutine call the subroutine is an atomic (with respect to an external viewer) update to state. The updates in the protected resource are implemented by a procedure call to a protected object, and tasks do no share state.  The synchronization construct also provides the means to specify parameter passing, both in and out of the task.
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==== Optional Annotations for Addressed Variables ====
  
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In the case of a sensing or actuating event, the updates of the action correspond to reads of monitored variables, and writes to controlled variables of the environment.
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Link To Addressed Variables!!!!!
  
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==== Implementing Events ====
 
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An event's role in the implementation is identified using the following extensions which are added to the event. Events used in task bodies are 'references' that make use of existing event definitions from the abstract development. The events are extended. to assist with translation, with a keyword indicating their role in the implementation.
 
  
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* Event implementation role.
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===== A Summary of Steps =====
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** Branch - In essence a task's event is split in the implementation; guards are mapped to branch conditions and actions are mapped to the branch body. If the branch refers to a Shared Machine event (procedureDef) then this is mapped to a simple procedure call.
 
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** Loop - The task's event guard maps to the loop condition and actions to to loop body. If the loop refers to a Shared Machine event then it is mapped to a simple procedure call.
 
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** ProcedureSynch - This usually indicates to the translator that the event maps to a subroutine, but an event in a task may not require a subroutine implementation if its role is simply to provide parameters for a procedure call.
 
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** ProcedureDef - Identifies an event that maps to a (potentially blocking) subroutine definition. Event guards are implemented as a conditional wait; in Ada this is an entry barrier, and in C may use a pthread condition variable .
 
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** Sensing - Identifies an event that maps to a read from the environment. If the environment is simulated without address variables then the sensing event is similar to a ProcedureSynch event, in that it has an update action that models assignment of a return value from a subroutine call. The event parameters act like the ''actualIn'' parameters of a ProcedureSynch event. On the other hand, if the event has addressed variables associated with its event parameters, then they map to direct reads from memory mapped variables in the generated code.
 
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** Actuating - Identifies an event that maps to a write to the environment. If the environment is simulated without address variables then the actuating event has no update action, the parameters act like ''actualOut'' parameters of a ProcedureSynch event. If a sensing event has addressed variables associated with its parameters then they map to direct writes to memory mapped variables in the generated code.
 
  
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Sensing (and actuating) can be viewed as a kind of synchronisation. Synchronisation between tasks and shared objects are represented as subroutine calls. The sensing/actuating synchronisations only occur between tasks and the environment. In implementable code, when an subroutine is defined, its formal parameters are replaced by actual parameter values at run-time. To assist the code generator we extend the Event-B parameters. We identify formal and actual parameters in the implementation, and add the following keywords to the event parameters, as follows:
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For a Tasking Machine definition:
 +
# Add the Tasking Machine type (Auto etc).
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# Add the task type (Periodic etc.).
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# Define the task priority.
 +
# Define the task body.
 +
# For each event, add the Event Type.
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# For each event parameter, add the Parameter Type.
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# Optionally define addressed variables.
  
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* Event parameter types - Note: formal parameters are place-holders in a subroutine; they are replaced by the actual parameters at call time.
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For a Shared Machine definition:
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** FormalIn or FormalOut - event parameters are extended with the ParameterType construct. Extension with formal parameters indicates a mapping to formal parameters in the implementation.
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# Add the ''SharedMachine'' Machine type.
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** ActualIn or ActualOut - Extension with an actual parameter indicates a mapping to an actual parameter in the implementation.
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# For each event, define the Event Type.
 +
# For each event parameter, define the Parameter Type.
  
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===== Addressed Variables =====
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==== Invoking the Translation ====
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When sensing monitored variables, or actuating controlled variables in the environment, we may wish to use explicit memory addresses for use in the final implementation, or perhaps in the environment simulation too. We can link a task's event parameters, and an Environ machines variables, with specific addresses and use these in the generated code.
 
  
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== References ==
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* To create the IL1 model,
 +
** Right-Click on the Main node, select ''Epsilon Translation/Translate Task Mch 2 IL1 EMF''.
 +
** Open the Resource Perspective.
 +
** Right-click on the ''sharedbuffer20100819Tutorial2'' project folder.
 +
** Select refresh, the ''.il1'' file should appear in the project.
 +
** Open and inspect the file, and view the source code by opening the IL1 Pretty Print view if desired.
  
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<references/>
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* To create the Event-B model of the implementation,
 +
** Return to the Rodin Modelling Perspective.
 +
** Right-Click on the Main node, select ''Epsilon Translation/Translate Task Mch 2 Event-B EMF''.
 +
** The ''sharedbuffer20100819bTasking'' project is generated, it can be opened and inspected.
  
 +
There are errors in the generated machines (not investigated the cause yet); these can be fixed in the following way.
 +
* Open a Machine in the Event-B Machine Editor.
 +
* Select the Edit tab.
 +
* Open the REFINES section, the error lies here.
 +
* The correct machine is refined, but choose a different machine to refine (any one, it doesn't matter).
 +
* Select the original refined machine again.
 +
* Save and clean the project, and the error should disappear.
 +
* Repeat for the same errors in the other machines; save and clean again.
 +
* The machines can viewed as normal using the Rodin editors.
  
 
[[Category:User documentation]]
 
[[Category:User documentation]]

Revision as of 10:47, 28 April 2011

THIS PAGE IS UNDER CONSTRUCTION !!!!!!

For more information contact Andy Edmunds - University of Southampton - mailto:ae2@ecs.soton.ac.uk

Tasking Event-B Tutorial Overview

This code generation tutorial supplements the Heating Controller tutorial example, and makes use of example projects from the download site. The code generation stage produces implementable Ada code, and also an Event-B project which models the implementation. The Ada code is produced using a pretty printer tool from an intermediate model, the Common Language model (IL1), generated by a translation tool. An overview of Tasking Event-B can be found on the Tasking_Event-B_Overview page.

The Heating Controller development has been refined to the point where we wish to add implementation constructs. The Event-B language is not expressive enough to fully describe the implementation. Tasking Event-B facilitates this final step to implementation, by extending Event-B with the necessary constructs. Event-B machines that are to be implemented (and their seen Contexts) are selected and added to a Tasking Development; the Tasking Development files have the file extension .tasking. The machines in the Tasking Development are then extended with implementation details.

The example/tutorial projects are,

Heating_ControllerTutorial_Completed An example project with a completed Tasking Development and IL1 model (post IL1 translation, but before Event-B translation).
Heating_ControllerTutorial_Completed_Gen Same as the example project above, but with Event-B model translations. The difference being that this development includes a model of the implementation. These are refinements that include a program counter to describe flow of execution in each task.
Heating_ControllerTutorial_Step1 A bare project for step 1 of the tutorial.
Heating_ControllerTutorial_Step2 A partially completed tasking development for steps 2, 3 and 4 of the tutorial.

Preliminaries

Before further discussion of the modelling aspects, we take a look at the PrettyPrint viewers. The PrettyPrinters make the viewing of IL1 and tasking models easier; it also provides a route to generate source code. The source code can easily be pasted from the IL1 Pretty Printer window into an the Ada source file .

The PrettyPrint View of a Tasking Development

To open the Tasking PrettyPrint viewer,

  • from the top-menu select Window/Show View/Other/Tasking Pretty Printer.

Note that the Tasking PrettyPrinter may have to be closed when editing the Tasking Development, since it can give rise to exceptions. The PrettyPrinter would need further work to make it robust, however it is intended only as a short-term solution.

  • Open the Heating_ControllerTutorial_Completed Project and switch to the Resource Perspective.
  • Open the .tasking model and inspect it. Clicking on the Main, Machine or Event nodes updates the pretty print window.

Viewing Source Code

aka. The PrettyPrint View of an IL1 Model.

To view Ada source code,

  • from the top-menu select Window/Show View/Other/IL1 Pretty Printer.
  • Open the Heating_ControllerTutorial_Completed Project and switch to the Resource Perspective.
  • Open the .il1 model and inspect it. Clicking on the Protected, Main Entry, or Task nodes updates the pretty print window.

Cleaning the Tasking Development

If the .tasking file has errors, then it may need cleaning. To do this right-click on the Main node, select Epsilon Translation/CleanUp. If a model has errors it can still be viewed by clicking on the Selection tab at the bottom of the tasking editor window.

The Tutorial

The steps needed to generate code from an Event-B model, in this tutorial, are as follows,

Creating The Tasking Development

  • Change to the Event-B Perspective.
  • Open the Heating_ControllerTutorial_Step1 Project.
  • Select the following Machines: Display_Update_Task1, Envir1, Heater_Monitor_Task1, Shared_Object1, Temp_Ctrl_Task1 and HC_CONTEXT.
  • Right-click and select Make Tasking Development/Generate Tasking Development.

The new Tasking Development will not be visible in the Event-B perspective, change to the resource perspective, open and inspect the new .tasking file. The Tasking Development contains (the EMF representation of) the machines that we wish to provide implementations for. In order to introduce the new concepts we have prepared a partially complete development.

Change to the Project Heating_ControllerTutorial_Step2 to begin the next step.

Providing the Annotations for Implementations

  • Close any Tasking Pretty Print Viewers that remain open. The incomplete model will give rise to exceptions.
  • Go to the to the Resource Perspective.
  • Open and inspect the .tasking machine.

The Display_Update_Task1, Envir1 and Shared_Object1 machines are incomplete. We will take the necessary steps to provide implementation details.

The Display_Update_Task1 Machine

In the partially complete tutorial project we already identified the Display_Update_Task1 as an Auto Task Tasking Machine, by adding the Auto Task extension. Auto Tasks are tasks that will be declared and defined in the Main procedure of the implementation. The effect of this is that the Auto Tasks are created when the program first loads, and then activated (made ready to run) before the Main procedure body runs. We have added the Periodic Task extension to the Auto Task, and set a period of 500 milliseconds. We will now complete the sequence that has been partially defined in the task body.

TO HERE!!!

  • Add Synchronisation between DIGet_Target_Temperature1 and SOGet_Target_Temperature1.
    • Expand the Auto Task Machine node.
    • Expand the Seq sub-tree.
    • Right-click on the Seq node and select New Child/Left Branch EventWrapper.
    • Provide the event label d1 using the properties view.
    • Right-click on Event Wrapper and select New Child/ Synch Events.
    • Select Synch Events and go to the drop-down menu of the Local Event property.
    • At this point the drop-down box displays a number of event names, select the second DIGet_Target_Temperature1 event.
    • Go to the drop-down menu of the Remote Event property.
    • From the list of events select the second SOGet_Target_Temperature1 event.

The Synch Events construct is used to implement Event Synchronisation. The next step wraps an event in an Event Wrapper in order to update the local state; there is no synchronisation as such but we will re-use the constructs that already exist.

  • Add the Wrapped Event TcalcWVal.
    • Expand the sub-tree of the second Seq node.
    • Right-click on the Seq node and select New Child/Left Branch EventWrapper.
    • Provide the event label w2 using the properties view.
    • Right-click on Event Wrapper and select New Child/ Synch Events.
    • Select Synch Events and go to the drop-down menu of the Local Event property.
    • From the list of events select the TcalcWVal event.

We have now completed the task body, and it just remains to complete provide details for the TWrite event. The TWrite event in WriterTsk is to be synchronized with the SWrite event in the SharedObj.

  • Add Event Extensions.
    • Right-click on the TWrite Event node.
    • Select New Child/Extension.
    • Right-click on the Extension node and select New Child/Implementation from the menu.
    • Go to the Implementation properties view and set the Implementation Type property to ProcedureSynch.
  • Identify Incoming and Outgoing parameters.
    • Right-click on the outAP node and add an Extension.
    • Right-click on the Extension and selectNew Child/Parameter Type.
    • Go to the Parameter Type properties view and set the Parameter Type property to actualOut.
    • Right-click on the inAP node and add an Extension.
    • Right-click on the Extension and selectNew Child/Parameter Type.
    • Go to the Parameter Type properties view and set the Parameter Type property to actualIn.
The Shared Machine

The next step is to identify the SharedObj machine as a Shared Machine. The SharedObj Machine will be extended using the Event-B EMF extension mechanism.

  • Right-click on the SharedObj Machine node in the .tasking file.
  • Select New Child/Extension.
  • Right-click on the Extension node and select New Child/Shared Machine from the menu.

We now show how to extend the SWrite event of the Shared Machine with details about its implementation. The SWrite event in SharedObj is to be synchronized with the TWrite event in the WriterTsk.

  • Identify SWrite as a Syncronisation.
    • Right-click on the SWrite Event node.
    • Select New Child/Extension.
    • Right-click on the Extension node and select New Child/Implementation from the menu.
    • Go to the Implementation properties view and set the Implementation Type property to ProcedureSynch.
  • Identify incoming and outgoing parameters.
    • Right-click on the inFP node and add an Extension.
    • Right-click on the Extension and selectNew Child/Parameter Type.
    • Go to the Parameter Type properties view and set the Parameter Type property to formalIn.
    • Right-click on the outFP node and add an Extension.
    • Right-click on the Extension and selectNew Child/Parameter Type.
    • Go to the Parameter Type properties view and set the Parameter Type property to formalOut.

Optional Annotations for Addressed Variables

Link To Addressed Variables!!!!!


A Summary of Steps

For a Tasking Machine definition:

  1. Add the Tasking Machine type (Auto etc).
  2. Add the task type (Periodic etc.).
  3. Define the task priority.
  4. Define the task body.
  5. For each event, add the Event Type.
  6. For each event parameter, add the Parameter Type.
  7. Optionally define addressed variables.

For a Shared Machine definition:

  1. Add the SharedMachine Machine type.
  2. For each event, define the Event Type.
  3. For each event parameter, define the Parameter Type.

Invoking the Translation

  • To create the IL1 model,
    • Right-Click on the Main node, select Epsilon Translation/Translate Task Mch 2 IL1 EMF.
    • Open the Resource Perspective.
    • Right-click on the sharedbuffer20100819Tutorial2 project folder.
    • Select refresh, the .il1 file should appear in the project.
    • Open and inspect the file, and view the source code by opening the IL1 Pretty Print view if desired.
  • To create the Event-B model of the implementation,
    • Return to the Rodin Modelling Perspective.
    • Right-Click on the Main node, select Epsilon Translation/Translate Task Mch 2 Event-B EMF.
    • The sharedbuffer20100819bTasking project is generated, it can be opened and inspected.

There are errors in the generated machines (not investigated the cause yet); these can be fixed in the following way.

  • Open a Machine in the Event-B Machine Editor.
  • Select the Edit tab.
  • Open the REFINES section, the error lies here.
  • The correct machine is refined, but choose a different machine to refine (any one, it doesn't matter).
  • Select the original refined machine again.
  • Save and clean the project, and the error should disappear.
  • Repeat for the same errors in the other machines; save and clean again.
  • The machines can viewed as normal using the Rodin editors.
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