Difference between revisions of "Tasking Event-B Tutorial"

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THIS PAGE IS UNDER CONSTRUCTION !!!!!!
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For more information contact Andy Edmunds - University of Southampton - mailto:ae2@ecs.soton.ac.uk
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<< I AM UPDATING THIS PAGE >>
  
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For more information contact Andy Edmunds - University of Southampton - mailto:ae2@ecs.soton.ac.uk
 
 
=== Tasking Event-B Tutorial Overview ===
 
=== 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.
+
This tutorial follows on from the abstract development described [http://wiki.event-b.org/index.php/Development_of_a_Heating_Controller_System here].
 +
 
 +
This code generation tutorial extends the Heating Controller tutorial example, and makes use of example projects from the download site. The code generation stage produces Java code, and also an Event-B model. It is a model of the implementation, and contains flow control variables that model the flow of execution through the task body. The Java code is produced from an intermediate model that is not visible to the user. The Common Language model (CLM), is generated from the Tasking Event-B by a translation tool. Java (and other implementations) may be generated from the CLM. An overview of Tasking Event-B can be found [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview here].
  
−
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.
+
In the example so far, the Heating Controller 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 modelling tasks, shared objects and the environment are identified, and extended with the appropriate implementation details.
  
−
The example/tutorial projects are,
+
The example/tutorial projects are are available from [https://github.com/andyed2003/codeGenExamples Git] or clone [https://github.com/andyed2003/codeGenExamples.git this].
  
 
{| border="1"
 
{| border="1"
−
|Heating_ControllerTutorial_Completed
+
|Heating_ControllerTutorial2_Completed
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|An example project with a completed Tasking Development and IL1 model (post IL1 translation, but before Event-B translation).
+
|An example project with an environment simulation. The environment variables are monitored and controlled using subroutine calls. The project contains a complete Tasking Development with generated Event-B and Java code.
 
|-
 
|-
−
|Heating_ControllerTutorial_Completed_Gen
+
|Heating_ControllerTutorial2_Partial1
−
|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.
+
|A project with the final decomposition completed, ready to begin Tasking Event-B Development.  
 
|-
 
|-
−
|Heating_ControllerTutorial_Step1
+
|Heating_ControllerTutorial2_Partial2
−
|A bare project for step 1 of the [[Code_Generation_Tutorial#The_Tutorial |tutorial]].
+
|A partially completed tasking specification for the continuation of the tutorial.
 
|-
 
|-
−
|Heating_ControllerTutorial_Step2
+
|TheoriesForCG
−
|A partially completed tasking development for steps 2, 3 and 4 of the [[Code_Generation_Tutorial#The_Tutorial |tutorial]].
+
|Contains the mathematical language translations; encoded as rules in a theory plug-in rule-base.
 
|}
 
|}
  
−
== Preliminaries ==
+
== Using the Tasking Extension ==
−
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,
 
The steps needed to generate code from an Event-B model, in this tutorial, are as follows,
−
* Step 1 - [[Tasking Event-B_Tutorial#Creating The Tasking Development|Create the tasking development]].
+
* Step 1 - [[Tasking Event-B_Tutorial#Adding the Implementation Level Refinement|Adding the Implementation Level Refinement]]
−
* Step 2 - [[Tasking Event-B_Tutorial#Providing the Annotations for Implementations|Add Tasking annotations]].
+
* Step 2 - [[Tasking Event-B_Tutorial#Pre-processing|Pre-processing]]
−
* Step 3 - [[Tasking Event-B_Tutorial#Optional Annotations for Addressed Variables|Add annotations for addressed variables (optional)]].
+
* Step 3 - [[Tasking Event-B_Tutorial#Adding Tasking Event-B|Add Tasking annotations]].
 
* Step 4 - [[Tasking Event-B_Tutorial#Invoking the Translation|Invoke translators]].
 
* Step 4 - [[Tasking Event-B_Tutorial#Invoking the Translation|Invoke translators]].
 +
=== Download and Copy the Theories ===
 +
The translations of the Event-B mathematical language to the target language constructs are specified as rules in the theory plug-in. Example rule files are included for the example, and are available in MathExtension from the [https://github.com/andyed2003/codeGenTheoryRepo Git] repository, or clone [https://github.com/andyed2003/codeGenTheoryRepo.git this]. After checking out the theories, they must be un-deployed, then re-deployed, ensuring that the builder cretaes all of the appropriate files. Right-Click on the theory file and select deploy to do this. If you already have a MathExtensions folder then it should be renamed else the import will be prevented. Files from this folder can be copied and deployed in the new folder if necessary.
  
−
==== Creating The Tasking Development ====
+
=== Adding the Implementation Level Refinement ===
−
* Change to the Event-B Perspective.
+
The final decomposition generates the machines that are required for code generation. However, it is not possible to edit the machines since they are machine generated, and therefore this is prohibited. In order to be able to modify the models we will refine the generated machines. This is where we begin with the ''Heating_ControllerTutorial2_Partial1'' project (Where the pre-processing steps, described below, have been performed already). To refine the machines we can use the automatic refinement feature, but this presents us with two problems that are dealt with in the pre-processing steps.  
−
* 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.
+
=== Pre-processing ===
  
−
* Change the tasking development, if necessary, so that the machine that models the environment is at the top of the tree of machines.
+
The pre-processing steps, described here, should be a temporary solution. The steps can be performed automatically, if appropriate changes are made to facilitate refinement of composed machines, and flattening of files.  
  
−
In the simulation implementation, elements of the Environ machine must be declared first.
+
* The Code Generator requires a flattened version of each machine; all of the Event-B elements should be available in the implementation level machine.
 +
* Composed machines are not currently able to be refined, so anything that requires synchronization of events requires some manual updates.
  
−
Change to the Project ''Heating_ControllerTutorial_Step2'' to begin the next step.
+
===== 'Flattening' the Implementation Machines =====
  
−
==== Providing the Annotations for Implementations ====
+
The temporary solution for flattening:
−
* Close any Tasking Pretty Print Viewers that remain open. The incomplete model will give rise to exceptions.
+
* Make events ''not extended''.
−
* Go to the to the Resource Perspective.
+
* Copy missing invariants.
−
* Open and inspect the ''.tasking'' machine.
 
  
−
The ''Temp_Ctrl_Task1Impl'', ''Envir1'' and ''Shared_Object1'' machines are incomplete. We will take the necessary steps to provide implementation details.  
+
I found the Event-B Machine Editor's synthesis view useful for this. Invariants can be copy-pasted into the implementation machine from the abstraction. (A dummy invariant can be added and selected for pasting)
  
−
===== The Temp_Ctrl_Task1Impl Machine =====
+
===== Providing the correct Composed Machine =====
−
In the partially complete tutorial project we have already identified the ''Temp_Ctrl_Task1Impl'' 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 Sensing between TCSense_Temperatures and ENSense_Temperatures'''.
+
The composed machine problem is sub-divided into two sub-problems. Firstly composed machines cannot be refined, and secondly when a machine is further decomposed there is no link between the first composed machine and the newly generated composed machine. So one or both of these problems may occur, depending on the number of decompositions.
−
** Expand the Temp_Ctrl_Task1Impl ''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 ''tc1'' 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''' ''TCSense_Temperatures'' event.
 
−
** Go to the drop-down menu of the ''Remote Event'' property.
 
−
** From the list of events select the '''first''' ''ENSense_Temperatures'' event.
 
  
−
By relating the sensing events in this way we describe a simulation of the interaction between the task and environment. The details of the interaction are embodied in the events themselves. This is implemented in the simulation code as a write to environment variables using a subroutine call.  
+
We must manually add the information to the composed machines to address these two problems.
  
−
Note that the Synch Events construct is used in several ways. We use it to implement [[Tasking Event-B Overview#Control Constructs|Event Synchronisation]]; sensing and actuation; and as a simple event wrapper. An example of its use in a simple event wrapper follows. The simple event wrapper is used to update local state; there is no synchronisation, as such, but we re-use the constructs that already exist rather than create new ones. We now add a wrapped event to the sequence,
+
The temporary solution for composed machines:
 +
* Modify the lowest level decomposed machine, HCtrl_M1_cmp, to ''include'' the implementation level machines (task names ending in *Impl). To do this,
 +
* open the composed machine editor. Open the INCLUDES edit feature.
 +
* Select the second drop-down box and find the *Impl version of each machine.
 +
* Save the composed machine.
 +
* Now add missing synchronizations to the composed machine. Add the ''Envir1Impl'' to the includes of HCtrl_M1_cmp.
 +
* Each composed event in the task, that synchronizes with the Environ machine, must have the remote event synchronization added manually. This can only be done by inspection of each composed event. We need to update Sense_Temperatures, Display_Current_Temperature, Actuate_OverHeat_Alram, Actuate_Heat_Source, Sense_Heater_Status, Actuate_NoHeat_Alarm, Sense_PressIncrease_Target_Temperature, Sense_PressDecrease_Target_Temperature, Display_Target_Temperature. One by one, expand the events in the composed events section of the composed machine editor; add a new event in the combines events section, select ''Envir1Impl'' and add the synchronizing event from the list-box to the right.
  
−
*'''Add the Wrapped Event TCCalculate_Average_Temperature'''.
+
=== Removing Non-deterministic Constructs ===
−
** 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 ''tc2'' 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 ''TCCalculate_Average_Temperature'' event.
 
  
−
The addition of the wrapped event, to the sequence, is simply specification of event ordering. It is implemented in code as a sequential subroutine call statement. We now specify event synchronisation between the task and shared object.  
+
It is also at this stage that any remaining non-deterministic constructs should be removed by replacing them with deterministic constructs.
  
−
*'''Add Synchronisation between TCGet_Target_Temperature2 and SOGet_Target_Temperature2'''.
+
TIP: Non-deterministic constructs cause strange characters to appear in the source code. If you see strange characters in the generated code, check for non-deterministic constructs in the implementation level machines.
−
** Further expand the ''Seq'' sub-tree until Eventwrapper tc3 appears.
 
−
** Right-click on the sibling ''Seq'' node (lowest in the tree) and select ''New Child/Left Branch EventWrapper''.
 
−
** Provide the event label ''tc4'' 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''' ''TCGet_Target_Temperature2'' event.
 
−
** Go to the drop-down menu of the ''Remote Event'' property.
 
−
** From the list of events select the '''second''' ''SOGet_Target_Temperature2'' event.
 
  
−
We have now completed the task body, and next provide additional details for events. In the first instance we focus on the the ''TCGet_Target_Temperature2 '' event in ''Temp_Ctrl_Task1Impl'' which is to be synchronized with the ''SOGet_Target_Temperature2 '' event in ''Shared_ObjectImpl''.
+
Alter_Temperature_Sensor1 in Envir1Impl: action becomes ts1 := ts1 + 1
 +
Alter_Temperature_Sensor2 in Envir1Impl: action becomes ts1 := ts1 + 1
 +
Alter_Heater_Status in Envir1Impl: action becomes hss := FALSE
 +
INITIALISATION in Heater_Monitor_TaskImpl: becomes shs := FALSE
  
−
*'''Add The Event Synchronisation Extension'''.
+
We also need to add a typing flag to an invariant. We need to add it in only one place, and this is where an invariant is used type a variable, in the Heating Controller machine. The flag is used to guide the translator to the typing invariant. This is because there may be more than one invariant involving that particular variable. They may also be added to guards where parameters are typed in guards, and the parameters are referred to in more than one guard.
−
** Right-click on the ''TCGet_Target_Temperature2'' Event node.
 
−
** Select ''New Child/Implementation'' from the menu.
 
−
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''ProcedureSynch''.
 
  
−
We have identified the event as one that partakes in a synchronisation.
+
* Go to the ''Heater_Monitor_TaskImpl typing_shs'' invariant.
 +
* Add the typing flag, by right-clicking on the invariant and selecting typing from the menu.
  
−
*'''Identify a parameter direction'''.
+
=== Adding Tasking Event-B ===
−
** Right-click on the ''tm'' node.
+
We will now work with the last of the tutorial projects, ''Heating_ControllerTutorial2_Partial2''.
−
** Select''New Child/Parameter Type''.
 
−
** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''actualIn''.
 
  
−
We have now identified the parameter as an actualIn (this models a call's return value).
+
*Setting Context attributes.
 +
**Open the project ''Heating_ControllerTutorial2_Partial2''.
 +
**Open the context, select the Tasking Context drop-down box, and select Tasking, as the type for the context.  
  
 +
This will ensure that code generation related static checks are performed. Select the 'Typing' option for Axioms ''axm3'' and ''axm4'', i.e. ''Min'' and ''Max'' are Typing axioms. The other axioms should be set to non-typing.
  
 +
Each Machine should be completed as follows.
 +
==== The Temp_Ctrl_TaskImpl Machine ====
 +
During this part of the tutorial we will cut and paste from ''Heating_ControllerTutorial2_Completed'' model when, specifying the task bodies, to save typing.
  
 +
*Set the Task Type to ''Auto Task''
 +
**Open The Tasking section of the Event-B editor.
 +
**Click on + to add a new Machine Type.
 +
**Ensure Auto Task is selected in the Drop-down box.
  
 +
''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.
  
−
Next we look at the sensing event ''TCSense_Temperatures'' event in ''Temp_Ctrl_Task1Impl''. Sensing (and actuating) can be viewed as a kind of synchronisation. The simulation code has a subroutine corresponding to the ''ENSense_Temperatures'' event in the Environ machine ''Envir1Impl''.  
+
*'''Add a new TaskBody'''.
 +
**Open Task Type (click on |> right arrow) in the Machine Type element
 +
**Set the task type to ''Periodic'',
 +
**Set a period of 250 milliseconds.  
 +
**Add a new Task Body section.
 +
**Copy and paste the task body from ''Heating_ControllerTutorial2_Completed/Temp_Ctrl_TaskImpl''
 +
**Save the model and rectify any problems highlighted.
 +
<!-- We now look at the sensing event ''Sense_Temperatures'' event in ''Temp_Ctrl_TaskImpl''. In order to assist with the translation we add the following annotation:
  
−
*'''Add The Sensed Event Extension'''.
+
*'''Add a Sensed Event Annotation'''.
−
** Right-click on the ''TCGet_Target_Temperature2'' Event node.
+
** Right-click on the ''Sense_Temperatures'' Event node.
 
** Select ''New Child/Implementation'' from the menu.
 
** Select ''New Child/Implementation'' from the menu.
−
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''ProcedureSynch''.
+
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''Sensing''.
  
−
We have identified the event as one that partakes in a synchronisation.
+
We now look at the actuating event ''Display_Current_Temperatures'' event in ''Temp_Ctrl_TaskImpl''. In order to assist with the translation we add the following annotation:
  
−
*'''Identify a parameter direction'''.
+
*'''Add an Actuating Event Annotation'''.
−
** Right-click on the ''tm'' node.
+
** Right-click on the ''Display_Current_Temperatures'' Event node.
−
** Select''New Child/Parameter Type''.
+
** Select ''New Child/Implementation'' from the menu.
−
** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''actualIn''.
+
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''Actuating''.
 +
-->
  
−
We have now identified the parameter as an actualIn (this models a call's return value).
+
==== The Shared Machine ====
  
−
===== The Shared Machine =====
+
The next step is to identify the ''Shared_ObjectImpl'' machine as a ''Shared Machine''.
 +
*Open the Tasking Section.
 +
*Add a Machine Type by clicking +.
 +
* Select ''Shared'' in the Machine Type drop Down box.
  
−
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.
+
==== The Environ Machine ====
−
* Right-click on the ''SharedObj'' Machine node in the ''.tasking'' file.
+
In the prepared machine we identify the ''Envir1Impl'' as an ''Environ Machine'',
−
* 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''.
+
*Open the Tasking Section in the Machine Editor
−
* '''Identify SWrite as a Syncronisation'''.
+
* Click on + to add a machine type.
−
** Right-click on the ''SWrite'' Event node.
+
*Select ''Environ Machine'' in the drop down box.  
−
** 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'''.
+
In the implementation, ''Environ Tasks'' are declared and defined in the ''Main'' procedure . The ''Envir1Impl'' machine models a task that simulates the environment, and can be used to generate simulation code. For deployment in a non-simulated environment the environ machine's generated code can be ignored. To specify the Environment task's behaviour we add edit the task body.
−
** 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''.
 
  
−
==== Optional Annotations for Addressed Variables ====
+
*'''Add the Task Details'''.
 +
**Open the Task Type section.
 +
**Set the task type to ''Periodic'',
 +
**Set a period of 100 milliseconds.
 +
**Add a new Task Body by clicking + in the Task Body section
 +
**Copy and paste the task body from ''Heating_ControllerTutorial2_Completed/Envir1Impl''
 +
**Save the model.
 +
**Resolve any problems that are highlighted.
  
−
Link To Addressed Variables!!!!!
+
When saving, the task body text is sent to the parser. If parsing is successful then a builder adds the structure to the underlying EMF tree. If parsing fails then an error panel displays the source of the error.
 +
<!-- The final step is to complete the ''Sense_Temperatures'' event. The event, being a kind of synchronization, synchronizes with the ''Sense_Temperatures'' event in the ''Temp_Ctrl_Task'' tasking machine. We annotate the model with sensing and actuating implementation types.
  
 +
*'''Add a Sensed Event Annotation'''.
 +
** Right-click on the ''Sense_Temperatures'' Event node.
 +
** Select ''New Child/Implementation'' from the menu.
 +
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''Sensing''.
  
−
===== A Summary of Steps =====
+
*'''Add an Actuating Event Annotation'''.
−
If generating environment simulation code:
+
** Right-click on the ''Display_Current_Temperatures'' Event node.
−
# Ensure the Environ Machine is first machine in the development.
+
** Select ''New Child/Implementation'' from the menu.
 +
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''Actuating''.
 +
-->
  
 +
=== A Summary of Steps ===
 
For a Tasking Machine definition:
 
For a Tasking Machine definition:
−
# Add the Tasking Machine type (Auto etc).
+
# Select the Tasking Machine type (Auto etc).
−
# Add the task type (Periodic etc.).
+
# Set the task type (Periodic etc.).
−
# Define the task priority.
+
# Set the task priority.
−
# Define the task body.
+
# Specify the task body.
−
# For each event, add the Event Type.
+
<!-- # For sensing/actuating events, add the Event Type. -->
−
# For each event parameter, add the Parameter Type.
 
−
# Optionally define addressed variables.
 
  
 
For a Shared Machine definition:
 
For a Shared Machine definition:
 
# Add the ''SharedMachine'' Machine type.
 
# Add the ''SharedMachine'' Machine type.
−
# For each event, define the Event Type.
 
−
# For each event parameter, define the Parameter Type.
 
  
−
==== Invoking the Translation ====
+
For an Environ Machine definition:
 +
# Make the type an Environ Machine type.
 +
# Set the task type Periodic; a shorter period than the shortest task period is best for simulation.
 +
# Set the task priority.
 +
# Specify the task body, it will contain a simulation of changes in the environment.
 +
# For each sensing/actuating event, add the Event Type.
 +
 
 +
== Invoking the Translators ==
  
−
* To create the IL1 model,
+
* To generate Ada code,
−
** Right-Click on the Main node, select ''Epsilon Translation/Translate Task Mch 2 IL1 EMF''.
+
** Right-Click on the composed machine, or any tasking machine in the development, select ''Code Generation/Translate Event-B to Ada''.
−
** Open the Resource Perspective.
+
** Open the generated ''code'' directory in the project to view the source files. A refresh will be necessary to make the code visible. The .gpr file has been provided for AdaCore GPS users.
−
** 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,
 
* To create the Event-B model of the implementation,
−
** Return to the Rodin Modelling Perspective.
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** Right-Click on the composed machine, or any tasking machine in the development, select ''Code Generation/Translate Tasking Event-B to Event-B''.
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** Right-Click on the Main node, select ''Epsilon Translation/Translate Task Mch 2 Event-B EMF''.
+
** The Event-B model should be updated with the flow control variables. Users are not able to manually edit the generated elements. The additions can be removed using the menu option ''Code Generation/Remove Generated Event-B''
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** The ''sharedbuffer20100819bTasking'' project is generated, it can be opened and inspected.
 
−
 
 
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There are errors in the generated machines (not investigated the cause yet); these can be fixed in the following way.
 
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* Open a Machine in the Event-B Machine Editor.
 
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* Select the Edit tab.
 
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* Open the REFINES section, the error lies here.
 
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* The correct machine is refined, but choose a different machine to refine (any one, it doesn't matter).
 
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* Select the original refined machine again.
 
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* Save and clean the project, and the error should disappear.
 
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* Repeat for the same errors in the other machines; save and clean again.
 
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* The machines can viewed as normal using the Rodin editors.
 
  
 +
=== Generated Code ===
 +
Generated code will be visible in the code directory, in the Event-B project. However a refresh of the workspace is required. The directory is visible in the resource view; or alternatively, click on the view menu in the Event-B perspective, select customize view, and uncheck the ''all file and folders'' filter.
 
[[Category:User documentation]]
 
[[Category:User documentation]]

Revision as of 09:57, 2 September 2013

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 tutorial follows on from the abstract development described here.

This code generation tutorial extends the Heating Controller tutorial example, and makes use of example projects from the download site. The code generation stage produces Java code, and also an Event-B model. It is a model of the implementation, and contains flow control variables that model the flow of execution through the task body. The Java code is produced from an intermediate model that is not visible to the user. The Common Language model (CLM), is generated from the Tasking Event-B by a translation tool. Java (and other implementations) may be generated from the CLM. An overview of Tasking Event-B can be found here.

In the example so far, the Heating Controller 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 modelling tasks, shared objects and the environment are identified, and extended with the appropriate implementation details.

The example/tutorial projects are are available from Git or clone this.

Heating_ControllerTutorial2_Completed An example project with an environment simulation. The environment variables are monitored and controlled using subroutine calls. The project contains a complete Tasking Development with generated Event-B and Java code.
Heating_ControllerTutorial2_Partial1 A project with the final decomposition completed, ready to begin Tasking Event-B Development.
Heating_ControllerTutorial2_Partial2 A partially completed tasking specification for the continuation of the tutorial.
TheoriesForCG Contains the mathematical language translations; encoded as rules in a theory plug-in rule-base.

Using the Tasking Extension

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

Download and Copy the Theories

The translations of the Event-B mathematical language to the target language constructs are specified as rules in the theory plug-in. Example rule files are included for the example, and are available in MathExtension from the Git repository, or clone this. After checking out the theories, they must be un-deployed, then re-deployed, ensuring that the builder cretaes all of the appropriate files. Right-Click on the theory file and select deploy to do this. If you already have a MathExtensions folder then it should be renamed else the import will be prevented. Files from this folder can be copied and deployed in the new folder if necessary.

Adding the Implementation Level Refinement

The final decomposition generates the machines that are required for code generation. However, it is not possible to edit the machines since they are machine generated, and therefore this is prohibited. In order to be able to modify the models we will refine the generated machines. This is where we begin with the Heating_ControllerTutorial2_Partial1 project (Where the pre-processing steps, described below, have been performed already). To refine the machines we can use the automatic refinement feature, but this presents us with two problems that are dealt with in the pre-processing steps.

Pre-processing

The pre-processing steps, described here, should be a temporary solution. The steps can be performed automatically, if appropriate changes are made to facilitate refinement of composed machines, and flattening of files.

  • The Code Generator requires a flattened version of each machine; all of the Event-B elements should be available in the implementation level machine.
  • Composed machines are not currently able to be refined, so anything that requires synchronization of events requires some manual updates.
'Flattening' the Implementation Machines

The temporary solution for flattening:

  • Make events not extended.
  • Copy missing invariants.

I found the Event-B Machine Editor's synthesis view useful for this. Invariants can be copy-pasted into the implementation machine from the abstraction. (A dummy invariant can be added and selected for pasting)

Providing the correct Composed Machine

The composed machine problem is sub-divided into two sub-problems. Firstly composed machines cannot be refined, and secondly when a machine is further decomposed there is no link between the first composed machine and the newly generated composed machine. So one or both of these problems may occur, depending on the number of decompositions.

We must manually add the information to the composed machines to address these two problems.

The temporary solution for composed machines:

  • Modify the lowest level decomposed machine, HCtrl_M1_cmp, to include the implementation level machines (task names ending in *Impl). To do this,
  • open the composed machine editor. Open the INCLUDES edit feature.
  • Select the second drop-down box and find the *Impl version of each machine.
  • Save the composed machine.
  • Now add missing synchronizations to the composed machine. Add the Envir1Impl to the includes of HCtrl_M1_cmp.
  • Each composed event in the task, that synchronizes with the Environ machine, must have the remote event synchronization added manually. This can only be done by inspection of each composed event. We need to update Sense_Temperatures, Display_Current_Temperature, Actuate_OverHeat_Alram, Actuate_Heat_Source, Sense_Heater_Status, Actuate_NoHeat_Alarm, Sense_PressIncrease_Target_Temperature, Sense_PressDecrease_Target_Temperature, Display_Target_Temperature. One by one, expand the events in the composed events section of the composed machine editor; add a new event in the combines events section, select Envir1Impl and add the synchronizing event from the list-box to the right.

Removing Non-deterministic Constructs

It is also at this stage that any remaining non-deterministic constructs should be removed by replacing them with deterministic constructs.

TIP: Non-deterministic constructs cause strange characters to appear in the source code. If you see strange characters in the generated code, check for non-deterministic constructs in the implementation level machines. 

Alter_Temperature_Sensor1 in Envir1Impl: action becomes ts1 := ts1 + 1
Alter_Temperature_Sensor2 in Envir1Impl: action becomes ts1 := ts1 + 1
Alter_Heater_Status in Envir1Impl: action becomes hss := FALSE
INITIALISATION in Heater_Monitor_TaskImpl: becomes shs := FALSE

We also need to add a typing flag to an invariant. We need to add it in only one place, and this is where an invariant is used type a variable, in the Heating Controller machine. The flag is used to guide the translator to the typing invariant. This is because there may be more than one invariant involving that particular variable. They may also be added to guards where parameters are typed in guards, and the parameters are referred to in more than one guard.

  • Go to the Heater_Monitor_TaskImpl typing_shs invariant.
  • Add the typing flag, by right-clicking on the invariant and selecting typing from the menu.

Adding Tasking Event-B

We will now work with the last of the tutorial projects, Heating_ControllerTutorial2_Partial2.

  • Setting Context attributes.
    • Open the project Heating_ControllerTutorial2_Partial2.
    • Open the context, select the Tasking Context drop-down box, and select Tasking, as the type for the context.

This will ensure that code generation related static checks are performed. Select the 'Typing' option for Axioms axm3 and axm4, i.e. Min and Max are Typing axioms. The other axioms should be set to non-typing.

Each Machine should be completed as follows.

The Temp_Ctrl_TaskImpl Machine

During this part of the tutorial we will cut and paste from Heating_ControllerTutorial2_Completed model when, specifying the task bodies, to save typing.

  • Set the Task Type to Auto Task
    • Open The Tasking section of the Event-B editor.
    • Click on + to add a new Machine Type.
    • Ensure Auto Task is selected in the Drop-down box.

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.

  • Add a new TaskBody.
    • Open Task Type (click on |> right arrow) in the Machine Type element
    • Set the task type to Periodic,
    • Set a period of 250 milliseconds.
    • Add a new Task Body section.
    • Copy and paste the task body from Heating_ControllerTutorial2_Completed/Temp_Ctrl_TaskImpl
    • Save the model and rectify any problems highlighted.

The Shared Machine

The next step is to identify the Shared_ObjectImpl machine as a Shared Machine.

  • Open the Tasking Section.
  • Add a Machine Type by clicking +.
  • Select Shared in the Machine Type drop Down box.

The Environ Machine

In the prepared machine we identify the Envir1Impl as an Environ Machine,

  • Open the Tasking Section in the Machine Editor
  • Click on + to add a machine type.
  • Select Environ Machine in the drop down box.

In the implementation, Environ Tasks are declared and defined in the Main procedure . The Envir1Impl machine models a task that simulates the environment, and can be used to generate simulation code. For deployment in a non-simulated environment the environ machine's generated code can be ignored. To specify the Environment task's behaviour we add edit the task body.

  • Add the Task Details.
    • Open the Task Type section.
    • Set the task type to Periodic,
    • Set a period of 100 milliseconds.
    • Add a new Task Body by clicking + in the Task Body section
    • Copy and paste the task body from Heating_ControllerTutorial2_Completed/Envir1Impl
    • Save the model.
    • Resolve any problems that are highlighted.

When saving, the task body text is sent to the parser. If parsing is successful then a builder adds the structure to the underlying EMF tree. If parsing fails then an error panel displays the source of the error.

A Summary of Steps

For a Tasking Machine definition:

  1. Select the Tasking Machine type (Auto etc).
  2. Set the task type (Periodic etc.).
  3. Set the task priority.
  4. Specify the task body.

For a Shared Machine definition:

  1. Add the SharedMachine Machine type.

For an Environ Machine definition:

  1. Make the type an Environ Machine type.
  2. Set the task type Periodic; a shorter period than the shortest task period is best for simulation.
  3. Set the task priority.
  4. Specify the task body, it will contain a simulation of changes in the environment.
  5. For each sensing/actuating event, add the Event Type.

Invoking the Translators

  • To generate Ada code,
    • Right-Click on the composed machine, or any tasking machine in the development, select Code Generation/Translate Event-B to Ada.
    • Open the generated code directory in the project to view the source files. A refresh will be necessary to make the code visible. The .gpr file has been provided for AdaCore GPS users.
  • To create the Event-B model of the implementation,
    • Right-Click on the composed machine, or any tasking machine in the development, select Code Generation/Translate Tasking Event-B to Event-B.
    • The Event-B model should be updated with the flow control variables. Users are not able to manually edit the generated elements. The additions can be removed using the menu option Code Generation/Remove Generated Event-B

Generated Code

Generated code will be visible in the code directory, in the Event-B project. However a refresh of the workspace is required. The directory is visible in the resource view; or alternatively, click on the view menu in the Event-B perspective, select customize view, and uncheck the all file and folders filter.

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