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

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=== Tasking Event-B ===
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For more information contact Andy Edmunds - University of Southampton - mailto:ae2@ecs.soton.ac.uk
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Tasking Event-B can be viewed as an extension of the existing Event-B language. We use the existing approaches of refinement and decomposition to structure a project that is suitable for a Tasking Development. During the modelling phase parameters are introduced to facilitate decomposition. As a result of the decomposition process, parameters become part of the interface that enables event synchronization. We make use of this interface and add information (see [[#Implementing Events]]) to facilitate code generation. The tasking extension consists of the constructs in the following table.
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=== 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 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].
 +
 
 +
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/Heating_ControllerTutorial_v0.2.0/ SVN].
  
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<center>
 
 
{| border="1"
 
{| border="1"
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!Construct
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|Heating_ControllerTutorial2_Completed
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!Options
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|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.
−
|-
 
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|Machine Type
 
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|DeclaredTask, [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines AutoTask], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Shared_Machines Shared], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#The_Environ_Machine Environ]
 
−
|-
 
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|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Control_Constructs Control]
 
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|Sequence, Loop, Branch, Event, Output
 
 
|-
 
|-
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|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines Task Type]
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|Heating_ControllerTutorial2_Partial1
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|Periodic(n), Triggered, Repeating, OneShot
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|A project with the final decomposition completed, ready to begin Tasking Event-B Development.
 
|-
 
|-
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|Priority
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|Heating_ControllerTutorial2_Partial2
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| -
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|A partially completed tasking specification for the continuation of the tutorial.
 
|-
 
|-
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|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Implementing_Events Event Role]
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|TheoriesForCG
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| Actuating, Sensing
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|Contains the mathematical language translations; encoded as rules in a theory plug-in rule-base.
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|-  
 
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|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Addressed_Variables Addressed Variable]
 
−
|Address, Base
 
 
|}
 
|}
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</center>
 
  
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==== Tasking Machines ====
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== Using the Tasking Extension ==
−
The following constructs relate to Tasking and Environ Machines, and provide implementation details. Timing of periodic tasks is not modelled formally. Tasking and Environ Machines model Ada tasks, so they can be implemented easily in Ada; in C using the pthread library, or in Java using threads.
+
The steps needed to generate code from an Event-B model, in this tutorial, are as follows,
 +
* Step 1 - [[Tasking Event-B_Tutorial#Adding the Implementation Level Refinement|Adding the Implementation Level Refinement]]
 +
* Step 2 - [[Tasking Event-B_Tutorial#Pre-processing|Pre-processing]]
 +
* 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]].
 +
=== 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.
 +
 
 +
=== 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.  
  
−
* Tasking Machines may be one of the following types:
+
* The Code Generator requires a flattened version of each machine; all of the Event-B elements should be available in the implementation level machine.  
−
** AutoTasks - Anonymous Tasks running from start-up.
+
* Composed machines are not currently able to be refined, so anything that requires synchronization of events requires some manual updates.
−
** Declared tasks - (Not currently used) A task template relating to an Ada ''tasktype'' declaration.  
 
  
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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.
+
===== 'Flattening' the Implementation Machines =====
  
−
* Tasking and Environ Machines options are:
+
The temporary solution for flattening:
−
** TaskType - Defines the scheduling, cycle and lifetime of a task. i.e. one-shot periodic or triggered. The period of a task is specified in milliseconds.
+
* Make events ''not extended''.
−
** Priority - An integer value is supplied, the task with the highest value priority takes precedence when being scheduled. The default priority is 5.
+
* Copy missing invariants.
  
−
==== Shared Machines ====
+
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)
−
A Shared Machine models a protected resource, such as a monitor. It may be implemented in Ada as a Protected Object, in C using mutex locking, or in Java as a monitor.
 
  
−
* A Shared Machine is identified using the ''Shared Machine'' annotation.
+
===== Providing the correct Composed Machine =====
  
−
==== The Environ 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.
−
An Environ machine is a model of the environment. It can be used to generate code for use in a simulation, or be discarded in the case that a simulated environment is not required.
 
  
−
* An Environ Machine is identified using the ''Environ Machine'' annotation.
+
We must manually add the information to the composed machines to address these two problems.
  
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=== Control of Program Flow ===
+
The temporary solution for composed machines:
−
At the implementation stage we need to think about controlling the flow of execution; and where interaction with the environment is concerned, how events should be implemented. The following section describes the constructs that we have introduced to facilitate this.
+
* Modify the lowest level decomposed machine, HCtrl_M1_cmp, to ''include'' the implementation level machines (task names ending in *Impl). To do this,
−
==== Control Constructs ====
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* open the composed machine editor. Open the INCLUDES edit feature.
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Each Tasking Machine has a ''task body'' which contains the flow control (algorithmic constructs).  
+
* 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.
  
−
* We have the following constructs available in the Tasking Machine body:
+
=== Adding Tasking Event-B ===
−
** Sequence - for imposing an order on events.
+
Each Machine should be completed as follows.
−
** Branch - choice between a number of mutually exclusive events.
+
==== The Temp_Ctrl_TaskImpl Machine ====
−
** Loop - event repetition while it's guard remains true.
+
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.
−
** Event - a wrapper for the Event-B element (soon to be redundant).
 
−
** Text Output - writes textual output to the screen.
 
  
−
The syntax for task bodies, as used in the Rose TaskBody editor, is as follows:
+
*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.
  
−
<br/>
+
''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.  
−
[[Image:Syntax2.png]]
 
−
<br/>
 
  
−
The ''String'' will be an event name, a variable name, or a text fragment to be output to the screen. The concrete syntax is shown in bold red font. '*' indicates 0 or more; [] indicates 0 or 1.
+
*'''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.
  
−
===== Event Translation =====
+
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.
−
When an event, used in the task body, is translated to an implementation its translation depends on where it is used in the task body. The mappings are relatively simple for branch, loop, and sequence; but, in addition to the parent construct, the Event translation depends on whether it is part of a synchronization. Obviously the simplest translation is when no synchronization is involved. The translator checks the composed machine to see if the event is paired in a combined event. We say that events is a Tasking machine are local, and that events in a Shared or Environ machine, are remote. If there is no synchronization, then the actions of the local event are expanded in-line in the subroutine body.  
 
  
−
<span style="color: RED">'''Caution''': As a result of the decomposition process, the tool can produce a remote event, without a corresponding local event. A local event, with no guards and skip action, must be added manually to the tasking machine, and composed machine in order to facilitate code generation. This relates to an implementation with a subroutine call, where there are no parameters passed, and no local updates i.e. remote updates only. The addition of the 'dummy' event will be automated in a pre-processing step in the near future. It is not necessary to have a dummy remote event if a remote event does not exist.</span>
+
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:
  
−
See [[ Outstanding Tooling Issues]]
+
*'''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''.
  
−
===== Synchronization =====
+
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:
  
−
Synchronization between local events (in AutoTasks) and remote events (in shared/Environ Machines) is determined using the composed machine. To use an event simply enter its name in the TaskBody editor. The translator will in-line any local actions, and add a call to perform remote updates, and obtain remote data.
+
*'''Add 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''.
  
−
Synchronization corresponds to:
+
==== The Shared Machine ====
−
* a subroutine call from task to shared machine, or,
 
−
* sensing or actuating of environment variables.
 
  
−
In the case of a subroutine call the subroutine is an atomic (with respect to an external viewer) update to state. The updates in the protected resource are implemented by a procedure call to a protected object, and tasks do not share state. The synchronization construct also provides the means to specify parameter passing, both in and out of the task.
+
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.
  
−
In the case of a sensing or actuating event, the updates of the action correspond to reads of monitored variables, and writes to controlled variables of the environment.
+
==== The Environ Machine ====
 +
In the prepared machine we identify the ''Envir1Impl'' as an ''Environ Machine'',
  
−
=== Implementing Events ===
+
*Add the ''Environ Machine'' extension.
−
An event's role in the implementation is identified by its parent in the task body. A description follows, in general terms, of the possible implementations of an event.
+
**Right-click on the Machine node in the Rose tree-editor.
 +
**Select the ''New Child Element/Auto Task Machine'' menu option.
  
−
<span style="color: BLUE">'''Note''': An event can be to referred only '''once''' in a task body specification. Of course, shared events (in Shared machines) can be re-used, but this is done through synchronization. The task body only refers to local events</span>
+
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.
  
−
* Event roles in implementation:
+
*'''Edit the TaskBody'''.
−
** Branching: an event is split in the implementation; guards are mapped to branch conditions, and actions are mapped to the branch body. If the branch synchronizes with a Shared machine's event then this is mapped to a procedure call.  
+
**Open the properties editor for the task body.
−
** Looping: as in branching, the event is split; the guard maps to the loop condition, and actions to to loop body. If the event synchronizes with a Shared Machine event then it is mapped to a procedure call.  
+
**Copy and paste the task body from ''Heating_ControllerTutorial2_Completed/Envir1Impl''
−
** Event: if the event is not contained in a branch or loop then it is one of the following:
+
**Set the task type to ''Periodic'',  
−
*** A local-only event - the event only contains local updates, which are expanded to update actions in the implementation. In this case guards not permitted in the event.
+
**Set a period of 100 milliseconds.  
−
*** A synchronizing event - local updates are expanded to become update actions in the implementation, remote updates are performed by subroutine call. Guards in the remote event may block; in Ada this is implemented as an entry barrier, and in C can be implemented using a pthread condition variable.
+
**Click on the Set Task Body button.
−
** Sensing annotation - This annotation is added to an event in the EMF tree. It identifies an event as one that maps to a read, from the environment. If the environment is simulated, i.e. without address variables, then the sensing event has an update action that models assignment of a return value from a subroutine call. If the event has addressed variables associated with its event parameters, then they map to direct reads from memory mapped variables in the generated code.
 
−
** Actuating - This annotation is added to an event in the EMF tree. It identifies an event as one that maps to a write, to some variable in the environment. If the environment is simulated, without address variables, then the actuating event has no update action. If a sensing event has addressed variables associated with its parameters then they map to direct writes, to memory mapped variables in the generated code.  
 
  
−
Sensing (and actuating) events make use of synchronization. The sensing/actuating synchronizations only occur between AutoTasks and Environ machines. The data exchange, in sensing and actuating events, is modelled by the event parameters, and the result from the decomposition step. Shared machine events are mapped to subroutine declarations, and their parameters are always implemented as formal parameters. Formal parameters are place-holders in a subroutine; they are replaced by the actual parameters at run-time. To assist the code generator, we automatically identify the parameter direction during translation. We identify them as either ''in'' or ''out'' parameters.  
+
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.
  
−
===== Addressed Variables =====
+
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.
−
When sensing monitored variables, or actuating controlled variables, in the environment we can use explicit memory addresses. We can link a task's event parameters, and an Environ machines machine variables with specific addresses, we then implement these in such a way that we can read/write from these in the generated code. <span style="color: RED">Addressed variables are on the TODO list</span>, see [[ Outstanding Tooling Issues]]
 
  
−
=== Theories, for Generating Code ===
+
*'''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''.
  
−
See [http://wiki.event-b.org/index.php/The_Use_of_Theories_in_Code_Generation The Use of Theories in Code Generation]
+
*'''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''.
  
−
=== State-Machines and Code Generation ===
+
=== A Summary of Steps ===
 +
For a Tasking Machine definition:
 +
# Add the Tasking Machine type (Auto etc).
 +
# Set the task type (Periodic etc.).
 +
# Set the task priority.
 +
# Specify the task body.
 +
# For sensing/actuating events, add the Event Type.
  
 +
For a Shared Machine definition:
 +
# Add the ''SharedMachine'' Machine type.
  
−
See [http://wiki.event-b.org/index.php/State-Machines_and_Code_Generation State Machines and Code Generation]
+
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.
  
−
== References ==
+
== Invoking the Translators ==
  
−
<references/>
+
* 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.
 
[[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.

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