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

From Event-B
(Difference between pages)
Jump to navigationJump to search
imported>Andy
 
imported>Andy
 
Line 1: Line 1:
=== Tasking Event-B ===
+
THIS PAGE IS UNDER CONSTRUCTION !!!!!!
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.
+
 
 +
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,
  
<center>
 
 
{| border="1"
 
{| border="1"
!Construct
+
|HeatingController20110429Demo
!Options
+
|An example project with a completed Tasking Development and IL1 model (post IL1 translation, but before Event-B translation).
 
|-
 
|-
|Machine Type
+
|HeatingController20110429Tasking
|[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 Shared], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#The_Environ_Machine Environ]
+
|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.
 
|-
 
|-
|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Control_Constructs_used_in_the_Task_body Task body]
+
|HeatingController20110429Tutorial
|Sequence, Loop, Branch, Event, Output
+
|A bare project for step 1 of the [[Code_Generation_Tutorial#The_Tutorial |tutorial]].
 
|-
 
|-
|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines Task Type]
+
|HeatingController20110429Tutorial2
|Periodic, Repeating, OneShot
+
|A partially completed tasking development for steps 2 and 3 of the [[Code_Generation_Tutorial#The_Tutorial |tutorial]].
|-
 
|Priority
 
| n
 
 
|}
 
|}
</center>
 
 
==== Tasking Machines ====
 
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 map easily to Ada; and can implemented in C using the pthread library, or in Java using threads.
 
 
* Tasking Machines may be one of the following types:
 
** AutoTasks - Anonymous Tasks running from start-up.
 
 
''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.
 
 
* Tasking and Environ Machines options are:
 
** 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.
 
** Priority - An integer value is supplied, the task with the highest value priority takes precedence when being scheduled. The default priority is 5.
 
 
==== Shared Machines ====
 
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.
 
 
* A Shared Machine is identified using the ''Shared Machine'' annotation.
 
 
==== The Environ Machine ====
 
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.
 
 
* An Environ Machine is identified using the ''Environ Machine'' annotation.
 
 
=== Control of Program Flow ===
 
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.
 
==== Control Constructs used in the Task body ====
 
Each Tasking Machine has a ''task body'' which contains the flow control (algorithmic constructs).
 
 
* We have the following constructs available in the Tasking Machine body:
 
** Sequence - for imposing an order on events.
 
** Branch - choice between a number of mutually exclusive events.
 
** Loop - event repetition while it's guard remains true.
 
** Event - a wrapper for the Event-B element (soon to be redundant). 
 
** Text Output - writes textual output to the screen.
 
 
The syntax for task bodies, as used in the Rose TaskBody editor, is as follows:
 
 
<br/>
 
[[Image:Syntax2.png]]
 
<br/>
 
 
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.
 
  
==== Translating Branches ====
+
== Preliminaries ==
In the explanation that follows, there may be a number of sub-branches, so we index the events of sub-branches (if they exist) with ''i''. Events can be used in the branching constructs, ''if'', ''elseif'' or ''else'', in the following way,
+
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''.
  
if evt_1
+
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.
[ elseif evt_i ]*
 
else evt _ n
 
  
where i = 2..(n-1)
+
* Open the ''HeatingController20110429Demo'' 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.
  
The events are translated to pseudocode in the following way:
+
==== Viewing Source Code ====
 +
aka. The PrettyPrint View of an IL1 Model.
  
if( g_1 ) then a_1
+
To view Ada source code,
[ elsif( g_i ) then a_i end ]*
+
* from the top-menu select ''Window/Show View/Other/IL1 Pretty Printer''.
else a_n end
+
* Open the ''HeatingController20110429Demo'' 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.
  
However, the guards of each branch must be disjoint; and of all branches must be complete.
+
==== 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.
  
So the guards of each event should be as follows;
+
== The Tutorial ==
 +
The steps needed to generate code from an Event-B model, in this tutorial, are as follows,
 +
* Step 1 - [http://wiki.event-b.org/index.php/Code_Generation_Tutorial#Creating_The_Tasking_Development Create the tasking development].
 +
* Step 2 - [http://wiki.event-b.org/index.php/Code_Generation_Tutorial#Providing_the_Annotations_for_Implementations Add annotations]
 +
* Step 3 - [http://wiki.event-b.org/index.php/Code_Generation_Tutorial#Invoking_the_Translation Invoke translators].
  
if evt_1 = g_1 -> a_1                // evt_1
+
==== Creating The Tasking Development ====
[ elseif not(g_(i-1)) & g_i -> a_i ] // evt_i starting from ''i'' = 2
+
* Change to the Event-B Perspective.
else not(g_(i-1)) -> a_n            // there of no guards ''g_n''
+
* Open the ''HeatingController20110429Tutorial'' Project.
 +
* Select the following Machines: Display_Update_Task1, Envir1, Heater_Monitor_Task1, SharedObject1, Temp_Ctrl_Task1 and HC_CONTEXT.
 +
* Right-click and select ''Make Tasking Development/Generate Tasking Development''.
  
In each sub-branch the guards of the preceding branches are negated, and the current guard added. The current guard is translated to the branch condition in the code, and the other guards are redundant. The ''else'' branch is an exception since it has no guard of its own. In a future enhancement we can produce proof obligations to show that the branch is disjoint and guard coverage is complete.
+
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.  
  
===== Event Translation =====
+
Change to the Project ''HeatingController20110429Tutorial2'' to begin the next step.
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; but, in addition to the parent construct, the Event translation depends on whether it is part of a synchronization. Obviously 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. We say that events is a Tasking machine are local, and that events in a Shared or Environ machine, are remote. If there is no synchronization, then the actions of the local event are expanded in-line in the subroutine body.  
 
  
<span style="color: RED">'''Note''': As a result of the decomposition process, the decomposition tool can produce a remote event, without a corresponding local event. This happens when modelling a task that updates a (remote) shared machine, but does not pass any parameters and has no local update. A local event, with no guards and skip action, must be added manually to the tasking machine, and also added to the composed machine. The code generator will then create an implementation with a subroutine call (with no parameters) causing only remote updates. The addition of the 'dummy' event will be automated in the future. It is not necessary to have a dummy remote event if a remote event does not exist.</span>
+
==== 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.
  
See [[ Outstanding Tooling Issues]]
+
The ''WriterTsk'' and ''SharedObj'' machines are incomplete. We will take the steps to necessary to provide implementation details.
  
===== Synchronization =====
+
===== The WriterTsk Machine =====
 +
In the partially complete tutorial project we already identified the ''WriterTsk'' 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 250 milliseconds. We will now complete the sequence that has been partially defined in the task body.
  
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.
+
*'''Add Synchronisation between TWrite and SWrite'''.
 +
** 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 ''w1'' 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 ''TWrite'' event.
 +
** Go to the drop-down menu of the ''Remote Event'' property.
 +
** From the list of events select the ''SWrite'' event.
  
Synchronization corresponds to:
+
The Synch Events construct is used to implement [http://wiki.event-b.org/index.php/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.
* a subroutine call from task to shared machine, or,
 
* sensing or actuating of environment variables.
 
  
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 not share state. The synchronization construct also provides the means to specify parameter passing, both in and out of the task.
+
*'''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.
  
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.
+
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''.
  
=== Implementing Events ===
+
*'''Identify Incoming and Outgoing parameters'''.
An event's role in the implementation is identified by its parent in the task body. A description follows, in general terms, of the possible implementations of an event.
+
** 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''.
  
<span style="color: BLUE">'''Note''': An event can be to referred only '''once''' in a task body specification. Of course, shared events (in Shared machines) can be re-used, but this is done through synchronization. The task body only refers to local events</span>
+
===== The Shared Machine =====
  
* Event roles in implementation:
+
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.
** Branching: an event is split in the implementation; guards are mapped to branch conditions, and actions are mapped to the branch body. If the branch synchronizes with a Shared machine's event then this is mapped to a procedure call.
+
* Right-click on the ''SharedObj'' Machine node in the ''.tasking'' file.
** Looping: as in branching, the event is split; the guard maps to the loop condition, and actions to to loop body. If the event synchronizes with a Shared Machine event then it is mapped to a procedure call.  
+
* Select ''New Child/Extension''.
** Event: if the event is not contained in a branch or loop then it is one of the following:
+
* Right-click on the ''Extension'' node and select ''New Child/Shared Machine'' from the menu.
*** A local-only event - the event only contains local updates, which are expanded to update actions in the implementation. In this case guards not permitted in the event.
 
*** A synchronizing event - local updates are expanded to become update actions in the implementation, remote updates are performed by subroutine call. Guards in the remote event may block; in Ada this is implemented as an entry barrier, and in C can be implemented using a pthread condition variable.
 
** Sensing annotation - This annotation is added to an event in the EMF tree. It identifies an event as one that maps to a read, from the environment. If the environment is simulated, i.e. without address variables, then the sensing event has an update action that models assignment of a return value from a subroutine call. 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.
 
** Actuating - This annotation is added to an event in the EMF tree. It identifies an event as one that maps to a write, to some variable in the environment. If the environment is simulated, without address variables, then the actuating event has no update action. 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.  
 
  
Sensing (and actuating) events make use of synchronization. The sensing/actuating synchronizations only occur between AutoTasks and Environ machines. The data exchange, in sensing and actuating events, is modelled by the event parameters, and the result from the decomposition step. Shared machine events are mapped to subroutine declarations, and their parameters are always implemented as formal parameters. Formal parameters are place-holders in a subroutine; they are replaced by the actual parameters at run-time. To assist the code generator, we automatically identify the parameter direction during translation. We identify them as either ''in'' or ''out'' parameters.  
+
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''.
  
===== Addressed Variables =====
+
* '''Identify incoming and outgoing parameters'''.
When sensing monitored variables, or actuating controlled variables, in the environment we can use explicit memory addresses. We can link a task's event parameters, and an Environ machines machine variables with specific addresses, we then implement these in such a way that we can read/write from these in the generated code. <span style="color: RED">Addressed variables are on the TODO list</span>, see [[ Outstanding Tooling Issues]]
+
** Right-click on the ''inFP'' 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 ''formalIn''.
 +
** Right-click on the ''outFP'' 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 ''formalOut''.
  
=== Theories, for Generating Code ===
+
===== A Summary of Steps =====
  
See [http://wiki.event-b.org/index.php/The_Use_of_Theories_in_Code_Generation The Use of Theories in Code Generation]
+
For a Tasking Machine definition:
 +
# Add the Tasking Machine type (Auto etc).
 +
# Add the task type (Periodic etc.).
 +
# Define the task priority.
 +
# Define the task body.
 +
# For each event, add the Event Type.
 +
# For each event parameter, add the Parameter Type.
  
=== State-Machines and Code Generation ===
 
  
 +
For a Shared Machine definition:
 +
# Add the ''SharedMachine'' Machine type.
 +
# For each event, define the Event Type.
 +
# For each event parameter, define the Parameter Type.
  
See [http://wiki.event-b.org/index.php/State-Machines_and_Code_Generation State-Machines and Code Generation]
+
==== Invoking the Translation ====
  
== References ==
+
* 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.
  
<references/>
+
* 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 15:39, 27 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,

HeatingController20110429Demo An example project with a completed Tasking Development and IL1 model (post IL1 translation, but before Event-B translation).
HeatingController20110429Tasking 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.
HeatingController20110429Tutorial A bare project for step 1 of the tutorial.
HeatingController20110429Tutorial2 A partially completed tasking development for steps 2 and 3 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 HeatingController20110429Demo 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 HeatingController20110429Demo 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 HeatingController20110429Tutorial Project.
  • Select the following Machines: Display_Update_Task1, Envir1, Heater_Monitor_Task1, SharedObject1, 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 HeatingController20110429Tutorial2 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 WriterTsk and SharedObj machines are incomplete. We will take the steps to necessary to provide implementation details.

The WriterTsk Machine

In the partially complete tutorial project we already identified the WriterTsk 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 250 milliseconds. We will now complete the sequence that has been partially defined in the task body.

  • Add Synchronisation between TWrite and SWrite.
    • 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 w1 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 TWrite event.
    • Go to the drop-down menu of the Remote Event property.
    • From the list of events select the SWrite 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.
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.


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.