Difference between revisions of "Tasking Event-B Tutorial"

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For more information contact Andy Edmunds - University of Southampton - mailto:ae2@ecs.soton.ac.uk
 
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 ===
 +
 +
<span style="color: RED">'''Caution''': This Page is under Construction - some parts are incomplete</span>
 +
 
This tutorial follows on from the abstract development described [http://wiki.event-b.org/index.php/Development_of_a_Heating_Controller_System here].
 
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 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 [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview 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 implementable Ada 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 Ada 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. Ada (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 representing the implemented tasks, shared objects and environment (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 are available in the [http://deploy-eprints.ecs.soton.ac.uk/304/ e-prints archive], or on [https://codegenerationd.svn.sourceforge.net/svnroot/codegenerationd/Examples/HeatingController_Tutorial_v0.1.4/ SVN].
+
The example/tutorial projects are are available in the [http://deploy-eprints.ecs.soton.ac.uk/304/ e-prints archive], or on [https://codegenerationd.svn.sourceforge.net/svnroot/codegenerationd/Examples/Heating_ControllerTutorial_v0.2.0/ SVN].
  
 
{| border="1"
 
{| border="1"
|Heating_ControllerTutorial_Completed
+
|Heating_ControllerTutorial2_Completed
|An example project generating an environment simulation. Generates code, where environment variables are monitored and controlled using subroutine calls. Contains a completed Tasking Development and IL1 model.
+
|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 Ada code.
 
|-
 
|-
|Heating_ControllerTutorial_Completed_Gen
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|Heating_ControllerTutorial2_Partial1
|Same as the example project above, but additionally with Event-B model translations. The difference: 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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|A project with the final decomposition completed, ready to begin Tasking Event-B Development.  
 
|-
 
|-
|Heating_ControllerTutorial_Step1
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|Heating_ControllerTutorial2_Partial2
|A bare project for step 1 of the [[Code_Generation_Tutorial#The_Tutorial |tutorial]].
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|A partially completed tasking specification for the continuation of the tutorial.
 
|-
 
|-
|Heating_ControllerTutorial_Step2
+
|TheoriesForCG
|A partially completed tasking development for steps 2, and 4 of the [[Code_Generation_Tutorial#The_Tutorial |tutorial]] (step 3 not required here).
+
|Contains the mathematical language translations; encoded as rules in a theory plug-in rule-base.
|-
 
|Heating_Controller5AddressedSim_Completed
 
|A completed example that uses Addressed Variables in the tasks, and also in the environment simulation. Generates Memory Mapped IO for sensing and actuation. 
 
|-
 
|Heating_Controller5AddressedNotSim_Completed
 
|A completed example that uses Addressed Variables in the tasks only. Generates Deployable Memory Mapped IO for sensing and actuation. Similar to above but we discard the environment task from generated code.  
 
 
|}
 
|}
 
== 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.
 
  
 
== Using the Tasking Extension ==
 
== Using the Tasking Extension ==
 
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]].
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* 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#Providing the Annotations for Implementations|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. Two rule files are included for the example, and are available in the [https://codegenerationd.svn.sourceforge.net/svnroot/codegenerationd/Examples/Heating_ControllerTutorial_v0.2.0/ SVN]. The files can be downloaded and copied into an Event-B project called ''MathExtensions''. The theory must then be deployed. Right-Click on the theory file and select deploy to do this. The non-Event-B project, the original download may now be deleted.
  
==== Creating The Tasking Development ====
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=== Adding the Implementation Level Refinement ===
* Change to the Event-B Perspective.
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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. 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 step. It is also at this stage that any remaining non-deterministic constructs should be removed by replacing them with deterministic constructs.
* 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.  
+
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.
  
* Change the tasking development, if necessary, so that the machine that models the environment is at the top of the list of machines.
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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
  
This is due to a temporary technical limitation in the translator.
+
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 is 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.
  
Change to the Project ''Heating_ControllerTutorial_Step2'' to begin the next step.
+
* 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.
  
==== Providing the Annotations for Implementations ====
+
=== Pre-processing ===
* 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 ''Temp_Ctrl_Task1Impl'', ''Envir1'' and ''Shared_Object1'' machines are incomplete. We will take the necessary steps to provide implementation details.  
+
The pre-processing step should be a temporary, the solutions can be incorporated into the tool to automatically perform the changes that are required.  
  
===== The Temp_Ctrl_Task1Impl Machine =====
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* The Code Generator requires a flattened version of each machine; all of the Event-B elements should be available in the implementation level 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 have provided a PrettyPrint view of the completed ''Temp_Ctrl_Task1Impl'' [http://wiki.event-b.org/images/Temp_Ctrl_Task1Impl.pdf here], it can be read in conjunction with the tutorial.
+
* Composed machines are not currently able to be refined, so anything that requires synchronization of events requires some manual updates.
  
The next step is to construct the task body using control constructs such as sequence, branch, loop and output. These constructs are discussed in the [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview overview] of Tasking Event-B. We will now complete the sequence that has been partially defined in the task body.
+
===== 'Flattening' the Implementation Machines =====
  
*'''Synchronize Sensing between TCSense_Temperatures and ENSense_Temperatures'''.
+
The temporary solution for flattening:
** Expand the Temp_Ctrl_Task1Impl ''Auto Task Machine'' node.
+
* Make events ''not extended''.
** Expand the ''Seq'' sub-tree.
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* Copy missing invariants.
** Right-click on the first ''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 in the properties view.
 
** 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 '''second''' ''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; and this is implemented in the simulation code by reading the values of the environment variables.
+
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)
  
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:
+
===== Providing the correct Composed Machine =====
  
*'''Add the Wrapped Event TCCalculate_Average_Temperature'''.
+
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 sub-tree of the second ''Seq'' node.
 
** Right-click on this (same as above) ''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 '''second''' ''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:
+
We must manually add the information to the composed machines to address these two problems.
  
*'''Add Synchronisation between TCGet_Target_Temperature2 and SOGet_Target_Temperature2'''.
+
The temporary solution for composed machines:
** Further expand the ''Seq'' sub-tree until Eventwrapper tc3 appears.
+
* Modify the lowest level decomposed machine, HCtrl_M1_cmp, to ''include'' the implementation level machines (task names ending in *Impl). To do this,
** Right-click on the sibling ''Seq'' node (lowest in the tree) and select ''New Child/Left Branch EventWrapper''.
+
* open the composed machine editor. Open the INCLUDES edit feature.
** Provide the event label ''tc4'' using the properties view.
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* Select the second drop-down box and find the *Impl version of each machine.
** Right-click on Event Wrapper and select ''New Child/ Synch Events''.
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* Save the composed machine.
** Select ''Synch Events'' and go to the drop-down menu of the ''Local Event'' property.
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* Now add missing synchronizations to the composed machine. Add the ''Envir1Impl'' to the includes of HCtrl_M1_cmp.
** At this point the drop-down box displays a number of event names, select the '''second''' ''TCGet_Target_Temperature2'' event.
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* 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.
** 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_Object1Impl''.  
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=== Adding Tasking Event-B ===
 +
Each Machine should be completed as follows.
 +
==== The Temp_Ctrl_TaskImpl Machine ====
 +
Continuing with the tutorial project ''Heating_ControllerTutorial2_Partial2'', we need to make changes to the following machines. During the tutorial we will cut and paste from ''Heating_ControllerTutorial2_Completed'' model when, specifying the task bodies, to save typing.
  
*'''Add The Event Synchronisation Extension'''.
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*Add the ''Auto Task'' extension.
** Navigate to the list of events in the machine.
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**Right-Click on the Machine node in the Rose tree-editor,
** Right-click on the ''TCGet_Target_Temperature2'' Event node.
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**and click on ''New Child Element/Auto Task Machine'' menu option.
** 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. The corresponding event in the Shared machine is dealt with [http://wiki.event-b.org/index.php/Tasking_Event-B_Tutorial#The_Shared_Machine here]
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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.  
  
*'''Identify a parameter direction'''.
+
*'''Edit the TaskBody'''.
** Right-click on the ''tm'' node.
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**Open the properties editor for the task body.
** Select''New Child/Parameter Type''.
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**Copy and paste the task body from ''Heating_ControllerTutorial2_Completed/Temp_Ctrl_TaskImpl''
** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''actualIn''.
+
**Set the task type to ''Periodic'',
 +
**Set a period of 250 milliseconds.
 +
**Click on the Set Task Body button.
  
We have now identified the parameter as an actualIn (this models a call's return value).
+
The task body is parsed, and if successful will add the structure to the EMF tree. If parsing is not successful an error panel will display the source of the error.
  
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. Synchronisation between tasks and shared objects are represented as subroutine calls. The sensing/actuating synchronisations only occur between tasks and the environment.
+
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 ''TCSense_Temperatures'' 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 ''Sensing''.
 
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''Sensing''.
  
We have identified the event as a sensing event. Now we add the parameter direction:
+
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 parameter directions'''.
+
*'''Add an Actuating Event Annotation'''.
** Right-click on the ''t1'' 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''.
** Right-click on the ''t2'' node.
 
** 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 parameters as an actualIn (modelling a received value from the environment).
+
==== The Shared Machine ====
  
===== The Shared Machine =====
+
The next step is to identify the ''Shared_ObjectImpl'' machine as a ''Shared Machine''.
 
+
* Right-click on the ''Shared_Object'' Machine node in the Rose tree-editor.
The next step is to identify the ''Shared_Object1Impl'' machine as a ''Shared Machine''. A PrettyPrint view of the [http://wiki.event-b.org/images/Shared_Object1Impl.pdf Shared_Object1Impl] shared machine can be read in conjunction with the text.
 
* Optionally collapse open branches of the EMF editor to remove clutter. 
 
* Right-click on the ''Shared_Object'' Machine node in the ''.tasking'' file.
 
 
* Select ''New Child/Shared Machine'' from the menu.
 
* Select ''New Child/Shared Machine'' from the menu.
  
We now show how to extend the ''SOGet_Target_Temperature2'' event of the Shared Machine with details about its implementation. The ''SOGet_Target_Temperature2'' event in ''Shared_Object1Impl'' synchronizes with the ''TCGet_Target_Temperature2'' event in the '' Temp_Ctrl_Task1Impl''.
+
==== The Environ Machine ====
 +
In the prepared machine we identify the ''Envir1Impl'' as an ''Environ Machine'',
  
* '''Identify SOGet_Target_Temperature2 as a Synchronized event'''.
+
*Add the ''Environ Machine'' extension.  
** Right-click on the ''SOGet_Target_Temperature2 '' Event node.
+
**Right-click on the Machine node in the Rose tree-editor.
** Select ''New Child/Implementation'' from the menu.
+
**Select the ''New Child Element/Auto Task Machine'' menu option.
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''ProcedureSynch''.
 
  
* '''Identify the outgoing (return) parameter'''.
+
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 ''tm'' node.
 
** Select ''New Child/Parameter Type''.
 
** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''formalOut''.
 
  
===== The Environ Machine =====
+
*'''Edit the TaskBody'''.
In the prepared machine we have identified the ''Envir1Impl'' as an ''Environ Machine'', by adding the ''Environ Machine'' extension. ''Envir1Impl'' 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; we provide details of non-simulated code using addressed variables later. As before, a PrettyPrint view is available [http://wiki.event-b.org/images/Envir1Impl_2.pdf here]. In the prepared Environment Machine we have already added a ''Periodic Task'' extension, and set a period of 100 milliseconds.
+
**Open the properties editor for the task body.
+
**Copy and paste the task body from ''Heating_ControllerTutorial2_Completed/Envir1Impl''
We will now complete the sequence that has been partially defined in the task body. The following specification models simulation of a temperature change; the temperature value is represented by a monitored variable in the environment. The generated code simulates the temperature change in the environment by changing the monitored value.
+
**Set the task type to ''Periodic'',  
 +
**Set a period of 100 milliseconds.  
 +
**Click on the Set Task Body button.
  
*'''Model Temperature Change in the environment'''.
+
When clicking on Set Task Body, the task body text is sent to the parser. If parsing is successful then a builder adds the structure to the EMF tree. If parsing fails then an error panel displays the source of the error.
** Optionally collapse open branches of the EMF editor to remove clutter. 
 
** Expand the Environ1Impl ''Environ Machine'' node.
 
** Expand the ''Seq'' sub-tree fully.
 
** Right-click on the last ''Seq'' node in the tree and and select ''New Child/Left Branch EventWrapper''.
 
** Provide the event label ''e4'' 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''' ''ENAlter_Temperature_Sensor1'' event.
 
  
Output to the screen during the simulation can be specified as follows:
+
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.
  
*'''Text Output during Simulation.'''.
+
*'''Add a Sensed Event Annotation'''.
** Right-click on the last ''Seq'' node in the tree and and select ''New Child/Right Branch Output''.
+
** Right-click on the ''Sense_Temperatures'' Event node.
** Select the ''Output'' node, and in the properties menu select the ''Element'' property drop down box.
 
** Select the ''last'' variable ''ctd'' that appears in the list.
 
** In the ''Text'' property field, add a textual description to accompany the text output.
 
 
 
The generated code will print the text, and the value of the variable, to the screen. The next step is to identify the ''ENAlter_Temperature_Sensor1'' as a ''ProcedureDef''. This event enables the environment to manipulate the monitored variable.
 
 
 
* '''Identify ENAlter_Temperature_Sensor1 as a ProcedureDef event'''.
 
** Right-click on the ''ENAlter_Temperature_Sensor1'' 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 ''ProcedureDef''.
+
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''Sensing''.
 
 
The final step is to complete the ''ENSense_Temperatures'' event. The event is a sensing event, sensing is a kind of synchronisation, it synchronises with the ''TCSense_Temperatures'' event in the ''Temp_Ctrl_Task1'' tasking machine. We add formal parameters annotations corresponding to the actual parameters that we have already defined in the task.
 
  
*'''Add The Sensed Event Extension'''.
+
*'''Add an Actuating Event Annotation'''.
** Right-click on the ''ENSense_Temperatures'' Event node.
+
** Right-click on the ''Display_Current_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 ''Sensing''.
+
** Go to the Implementation properties view and set the ''Implementation Type'' property to ''Actuating''.
 
 
We have identified the event as a sensing event. Now we add the parameter direction:
 
 
 
*'''Identify parameter directions'''.
 
** Right-click on the ''t1'' node.
 
** Select''New Child/Parameter Type''.
 
** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''formalOut''.
 
** Right-click on the ''t2'' node.
 
** Select''New Child/Parameter Type''.
 
** Go to the ''Parameter Type'' properties view and set the ''Parameter Type'' property to ''formalOut''.
 
 
 
We have now identified the parameters as an formalOut (modelling a simulation's subroutine call return value). This completes the necessary annotations for the simulation, and we can proceed to the translation step. In the event that memory mapped IO is required (non-simulation) then addresses can be added to the model at this stage, before translation takes place. See section on [http://wiki.event-b.org/index.php/Tasking_Event-B_Tutorial#Optional_Annotations_for_Addressed_Variables Addressed Variables] for details.
 
 
 
==== A Quick Check ====
 
 
 
It should now be possible to open the tasking PrettyPrinter view (Window menu) without errors. If the PrettyPrint fails, then this is a sign that the model has been incorrectly constructed. The point of failure (the extent of the printout before failure) may indicate the location of the error in the model.
 
 
 
===== A Summary of Steps =====
 
If generating environment simulation code:
 
# Ensure the Environ Machine is first machine in the development.
 
  
 +
=== A Summary of Steps ===
 
For a Tasking Machine definition:
 
For a Tasking Machine definition:
 
# Add the Tasking Machine type (Auto etc).
 
# Add 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.
 
  
 
For an Environ Machine definition:
 
For an Environ Machine definition:
 
# Make the type an Environ Machine type.
 
# Make the type an Environ Machine type.
# Make the task type Periodic; a shorter period than the shortest task period is best for simulation.
+
# Set the task type Periodic; a shorter period than the shortest task period is best for simulation.
# Define the task priority.
+
# Set the task priority.
# Define the task body, it will contain a simulation of changes in the environment.
+
# Specify the task body, it will contain a simulation of changes in the environment.
# For each event, add the Event Type.
+
# For each sensing/actuating event, add the Event Type.
# For each event parameter, add the Parameter Type.
 
# Optionally define addressed variables.
 
  
 
== Invoking the Translators ==
 
== 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 ''Heating_ControllerTutorial_Step2'' 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.
 
 
 
In the event that the translator fails check that the correct events have been selected in the ''synchEvents'' construct. This can be done by looking at each task's ''taskBody'' construct, in the Tasking Pretty Printer view. In the PrettyPrinter view, each synchronization has a ''target'' and ''event'' seprated by dot-notation. The target is either the name of a shared machine or an environ machine. In this example check that the ''target'' refers to the correct machine, i.e. ''Envir1Impl'' rather than ''Envir1''; ''Temp_Ctrl_Task1Impl'' rather than ''Temp_Ctrl_Task1''; and ''SharedObject1Impl'', rather than ''SharedObject1''. After correcting any errors, invoke the translator again.
 
  
 
* To create the Event-B model of the implementation,
 
* To create the Event-B model of the implementation,
** Return to the Rodin Modelling Perspective.
+
** Right-Click on the composed machine, or any tasking machine in the development, select ''Code Generation/Translate Tasking Event-B to Event-B''.
** 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''
** The ''Heating_Controller5AGen'' project is generated, it can be opened and inspected.
 
 
 
There may be errors in the generated machines (the issue will disappear in a future release); 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.
 
 
 
== Optional Annotations for Addressed Variables ==
 
To use memory mapped IO (Addressed Variables) in our generated code we can specify which addresses to use in our [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Implementing_Events sensing and actuating events]. The addresses are added to the event parameters of  a Tasking Machine's sensing and actuating events. The addresses may also be added to the Environ machine's machine variables, for use in simulation. It should be noted that the use of addressed variables, in simulation, has to be done cautiously to prevent memory errors. In the current release the translator generates code for all of these situations, and the environment task should be discarded if simulation is not required.
 
 
 
We now add addressed variable to the ''TCSense_Temperatures'' event in ''Temp_Ctrl_Task1Impl'', a PrettyPrint view is available [http://wiki.event-b.org/images/AddressedVarsTask.pdf here]. 
 
 
 
* '''Add Address Information to Event Parameters'''.
 
** Right-click on the parameter node.
 
** Select ''New Child/Addressed Variable''.
 
** Go to the ''Addressed Variable'' properties view and set the ''Address'' and ''Base'' properties to appropriate values.
 
 
 
Reads of the monitored variables of the sensing event can therefore be made directly from the address specified. Their is also a ''base'' property which can be set to indicate the base of the property value. The default value is 16. The environment simulation may also make use of addressed variables, but in this case the extension is made to the Environ Machine machine variables and used as shown [http://wiki.event-b.org/images/AddressedVarsEnvir.pdf here].
 
 
 
Invocation of the translators proceeds as detailed above.
 
 
 
== Generated Code ==
 
The Ada Code generated by the translator is available at the following links:
 
 
 
for simulation of environment without addressed variables, [http://wiki.event-b.org/images/Code_Heating_ControllerTutorial_Completed.pdf Heating_ControllerTutorial_Completed]
 
 
 
for simulation of environment with addressed variables, [http://wiki.event-b.org/images/Code_Heating_Controller5AddressedSim_Completed.pdf Heating_Controller5AddressedSim_Completed]
 
 
 
Removal of the environment task from the ''Heating_Controller5AddressedSim_Completed'' should be deployable.
 
  
 +
=== Generated Code ===
 +
Generated code should be visible in the code directory, in the Event-B project. You can see the directory 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 09:46, 2 December 2011

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

Tasking Event-B Tutorial Overview

Caution: This Page is under Construction - some parts are incomplete

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 implementable Ada 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 Ada 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. Ada (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 in the e-prints archive, or on SVN.

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 Ada 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. Two rule files are included for the example, and are available in the SVN. The files can be downloaded and copied into an Event-B project called MathExtensions. The theory must then be deployed. Right-Click on the theory file and select deploy to do this. The non-Event-B project, the original download may now be deleted.

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. 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 step. 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 is 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.

Pre-processing

The pre-processing step should be a temporary, the solutions can be incorporated into the tool to automatically perform the changes that are required.

  • 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.

Adding Tasking Event-B

Each Machine should be completed as follows.

The Temp_Ctrl_TaskImpl Machine

Continuing with the tutorial project Heating_ControllerTutorial2_Partial2, we need to make changes to the following machines. During the tutorial we will cut and paste from Heating_ControllerTutorial2_Completed model when, specifying the task bodies, to save typing.

  • Add the Auto Task extension.
    • Right-Click on the Machine node in the Rose tree-editor,
    • and click on New Child Element/Auto Task Machine menu option.

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.

  • Edit the TaskBody.
    • Open the properties editor for the task body.
    • Copy and paste the task body from Heating_ControllerTutorial2_Completed/Temp_Ctrl_TaskImpl
    • Set the task type to Periodic,
    • Set a period of 250 milliseconds.
    • Click on the Set Task Body button.

The task body is parsed, and if successful will add the structure to the EMF tree. If parsing is not successful an error panel will display the source of the error.

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 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.

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:

  • Add an Actuating Event Annotation.
    • Right-click on the Display_Current_Temperatures Event node.
    • Select New Child/Implementation from the menu.
    • Go to the Implementation properties view and set the Implementation Type property to Actuating.

The Shared Machine

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

  • Right-click on the Shared_Object Machine node in the Rose tree-editor.
  • Select New Child/Shared Machine from the menu.

The Environ Machine

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

  • Add the Environ Machine extension.
    • Right-click on the Machine node in the Rose tree-editor.
    • Select the New Child Element/Auto Task Machine menu option.

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.

  • Edit the TaskBody.
    • Open the properties editor for the task body.
    • Copy and paste the task body from Heating_ControllerTutorial2_Completed/Envir1Impl
    • Set the task type to Periodic,
    • Set a period of 100 milliseconds.
    • Click on the Set Task Body button.

When clicking on Set Task Body, the task body text is sent to the parser. If parsing is successful then a builder adds the structure to the 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.
  • Add an Actuating Event Annotation.
    • Right-click on the Display_Current_Temperatures Event node.
    • 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:

  1. Add the Tasking Machine type (Auto etc).
  2. Set the task type (Periodic etc.).
  3. Set the task priority.
  4. Specify the task body.
  5. For sensing/actuating events, add the Event Type.

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 should be visible in the code directory, in the Event-B project. You can see the directory 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.