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Note that this page refers to the new textual SCCharts syntax (SCTX). See Converting Legacy Models (sct) on how to convert legacy files.

Semantics

For a detailed description of the basic concept and semantics of SCCharts please consult Sections 3.1 & 3.2 in the dissertation of Christian Motika.




SCCharts Statemachine

Each SCChart starts with the keyword scchart followed by an IDA ID can be any alpha-numerical combination, but must start with an alphabetical character or an underscore (a single underscore is prohibited). However, underscores are used to identify auto-generated constructs, so the modeler should not use them as prefix.

Simple States

One of the basic constructs of SCCharts is a simple state. A simple state does not have any inner behavior and can be connected via transitions to other states.

Initial State

To tell the program where to start, a state can be marked as initial. Exactly one state (per concurrent region, see concurrency) must be marked as initial.

Transitions


Transitions connect states. There are different kinds of Transitions, but we will restrict ourselves to the two basic types for now. (See below for more complex transitions.)

They can be guarded by a trigger that determines when this transition is enabled and they can have effects that are executed whenever this transition becomes active.

The exact syntax is as follows:

[immediate] [if condition] [do effect[; effect]*] (go | abort | join) to targetstate

Delayed Transitions

A delayed transition cannot trigger in the instance the parent state is entered. If a state is entered, they become active in the next tick. You can see this in the Simple example. Just write go to.

Immediate Transitions

Immediate transitions are checked as soon as their parent state is entered. Hence, the state can be entered and left within the same tick. Use the keyword immediate to create an immediate transition

Explicit Delay Behavior

UPCOMING

Transitions can be marked as delayed or auto explicitly. At the moment this is identical as not being immediate. However, in the upcoming 1.1 update, this will play a bigger role, when code generators can decide themselves if a transition has to be delayed or not.

Final State

A state can also be marked as final. A final state marks the end of a thread. If a final state is reached on root level, the program terminates.

scchart Simple {
	
  initial state A
  go to B 
  
  state B
  go to C 
  
  state C
  immediate go to A 
}
scchart Simple {
	
  initial state A
  auto go to B 
  
  state B
  delayed go to C 
  
  final state C
}




Declarations & Variables

Each scope (for now just the SCChart) can have a list of declarations. The SCChart code on the right gives an example. A declaration starts with the type, followed by a list of variable identifier. Each variables can be initialized with a specific value. 

Types

The following native types are supported: bool, int, float, string, host, and signal (see below)

Additionally, you can mark a declaration as extern and give it a string that will be used in the serialization of the final code, e.g., the name of a host type. You can then add variables as before.

Please note that most code generators will translate the semantical type float into a high-precision floating point host type (e.g. double in java).

Arrays

If you add brackets to a variable and specify cardinalities, you declare an array.

Constants

Declarations can be marked as constant, meaning that each occurrence is then replaced by the initialization because the variable is not allowed to be changed.

scchart Variables {
  input bool second
  output bool beep
  int i, j, k
  int arr[10]
  bool alarm = false
  const bool ON = 1
  extern "rObj" rail  
  
  initial state A
  go to B
  
  state B
}


Vectors

You can assign a whole vector to an array at once. 

scchart tuples {
  output int arr[5] = {1, 2, 3, 4, 5}

  initial state init {
    entry do arr = {6, 7, 8, 9, 10}
  }
}

To assign only certain values of an array, you can also use the ignore value placeholder. Consult the expression manual for further information.

scchart tuples {
  const int A = 1
  output int arr[3][2] = {{A,0}, {2,0}, {3,0}}

  initial state init
    do arr = {{arr[0] + 1, _}, _, {arr[2] + 1, _}} go to init
}

This would, for example, result in c code assignments as displayed on the right.

void logic(TickData* d) {
  d->_g0 = d->_GO;
  if (d->_g0) {
    d->arr[0][0] = 1;
    d->arr[0][1] = 0;
    d->arr[1][0] = 2;
    d->arr[1][1] = 0;
    d->arr[2][0] = 3;
    d->arr[2][1] = 0;
  }
  d->_g2 = d->_pg1;
  if (d->_g2) {
    d->arr[0][0] = d->arr[0] + 1;
    d->arr[2][0] = d->arr[2] + 1;
  }
  d->_g1 = d->_g0 || d->_g2;
}




Comments

You can simply use JavaDoc-style comments to comment you SCChart. The comments will appear in the synthesized diagram as comment boxes. You can toggle these boxes in your sidebar. 

Additionally, for documentation reason, you can annotate different elements to give them a user-defined style. E.g. colorize a state or comment box for visual effect. Use html-like color codes for different colors. Please read more on annotations in the section below.

/**
 * Getting there!
 */
scchart Root {
  /** Test */
  input bool second 
  output bool speaker 

  /**
    * Main region!
    */
  region main:

  /**	
    * The initial state
    * This is entered as soon as the program starts.
    */    
  @foreground f0f024
  @background ffffcc
  @backgroundTarget fff9ba
  initial state Superstate {
    initial state R1
  } 
  /** Transition */
  /** Transition 2 */
  join to S

  /**
    * The final state!
    * @foreground f00
    * @background a00
    */
  final state S
}






Hierarchy & Concurrency

Superstates

Superstates model hierarchy. Each nested superstate creates a new scope. The syntax is easy: just start a new scope via curly brackets after your initial state declaration.

A superstate can be exited by any transition preemption type. However, especially the termination (or join) is of interest as it is taken as soon as the superstate finishes (meaning a final state is reached.)

Regions

Regions model concurrency. They follow the initialize-update-read protocol if scheduling between different regions becomes necessary.

A termination transition is taken if all regions of the superstate have reached a final state.


scchart superstates {
  input bool F
	
  initial state init {
    initial state init
    if F go to done 
		
    final state done 	
  }
  join to done
	
  final state done
}
scchart concurrencies {
  input bool E, F 

  initial state EF {
    
    region handleF {
      initial state init
      if F go to done
	
      final state done
    }
		
    region handleE {
      initial state init
      if E go to done
	
      final state done
    }
	
  }
  join to done
	
  final state done
}

For Regions

You can automatically duplicate regions and access a region counter variable.

scchart IIIRO {
  input int I
  input bool R
  output bool O

  initial state IIO {
    entry do O = false

    initial state II {
      region main for i : 1 to 3 {
        initial state IWait
        if I == i go to IDone
	
        final state IDone
      }
    }
    do O = true join to Done 
		
    state Done
  }
  if R go to IIO 
}

This is also possible for a complete array.

scchart IIIRO {
  input int I
  input bool R
  output bool O
  input bool ACTIVE[10]

  initial state IIO {
    entry do O = false

    initial state II {
      region for i : ACTIVE {
        initial state IWait
        if ACTIVE[i] go to IDone 
	
        final state IDone
      }
    }
    do O = true join to Done 
	
    state Done
  }
  if Rgo to IIO 
}


Complex Final States

Complex Final states are final states that comprise inner behavior. Besides being a superstate, also actions and outgoing transitions count. Basically, any not simple final state without outgoing transitions is a complex final state.


Actions

Action in SCCharts are defined at the beginning of a state after the declarations.

Entry Action

An entry action is executed immediately when its state is entered. If the optional trigger is specified the effect(s) will only be executed if the trigger condition is true.

During Action

A during action is executed in each tick its state is active except when the state is entered. If an immediate during is used the action is also executed in the tick the state is entered. If the optional trigger is specified the effect(s) will only be executed if the trigger condition is true.

Exit Action

An entry action is executed when its state is left. Exit actions are considered inner behavior and are consequently suppressed if the state is strongly aborted. If the optional trigger is specified the effect(s) will only be executed if the trigger condition is true.

scchart Actions {
  input bool trigger
  output int effect
  initial state A
    go to B

  state B {
    entry do effect = 0
    entry if trigger do effect++
    during if trigger do effect++
    immediate during if trigger do effect++
    exit if trigger do effect *= 10
    initial state B1
      if trigger go to B2
    state B2
  }
}

Suspend

Suspend suppresses the inner behavior of a state, if is trigger is evaluated to true. If the immediate modifier is present the suspension can already be enabled in the tick the state is entered, otherwise the trigger is only checked in subsequent ticks. The weak modifier allows instantaneous inner behavior of a suspended state but the reached state is not memorized.

Weak suspend is not fully supported in 1.0 and may not be transformed or visualized (during simulation) correctly.

scchart Suspension {
  input bool S1, S2, S3, S4
  output int O = 0
  
  suspend if S1
  immediate suspend if S2
  weak suspend if S3
  immediate weak suspend if S3
  
  initial state A
    do O++ go to A
}

Complex Transitions

In Core SCCharts only simple transitions that originate from simple states and terminations for superstates are legit. However, there are more complex transition types if taking Extended SCCharts into account.

Abort

SCCharts knows two types of preemption: weak and strong aborts.

Semantically, a weak abort allows the behavior of the aborting superstate in the current tick to proceed before preemption, whereas strong aborts terminate the superstate immediately. In the diagram, strong aborts are depicted with a red circle decorator.

Count Delay

In a count delay transition, the transiton trigger has to become true multiple times before firing. 

Shallow History

If a superstate is entered via a shallow history transition, the superstate continues its execution at the point it was left excluding deeper hierarchies.

Deep History

With deep history transitions, the execution also recognizes deeper nesting levels, when re-entering the superstate.

Deferred

If a deferred transition is taken in the current tick, the target state will be entered in the next tick.


History and deferred transitions are not fully supported in 1.0 and may result in unexpected behavior when combined. They may not be visualized correctly during simulation.

Signals

Signals, as known from languages such as Esterel, are set to absent at the beginning of the tick. They can then be set to present during the current tick. Pure signals just know their activity state, whereas valued signals - in addition to their state also carry a value, which is persistent across ticks.



scchart Aborts {
  input bool I, S, W, Imm
  output int F = 0

  initial state A {

    initial state A0
    immediate if I && Imm go to A1
    if I go to A2

    final state A1
    final state A2
  }
  immediate if S && Imm do F = 1 abort to F1
  if S  do F = 2 abort to F2
  immediate if W && Imm  do F = 3 go to F3
  if W  do F = 5 go to F4
  do F = 5 join to F5

  final state F1
  final state F2
  final state F3
  final state F4
  final state F5
}
scchart ComplexTransitions {
  input bool CD, SH, DH, D
  output int F, F2  
  
  initial state A {
    entry do F = 0
    during do F++
    
    initial state AA {
      entry do F2 = 0
      during do F2++
    }
  }
  if 3 CD go to Wait

  state Wait
  if SH go to A shallow history
  if DH go to A history
  if D go to A deferred
  go to A
}

References

We will use the beep.sctx as example for referenced SCCharts.

scchart Beep {
	input bool second
	output bool beep = false
	
	initial state A
	if second do beep = true go to B 
	
	state B
	if second do beep = false go to A 
}

If you want to use another SCChart inside your model, you must first include it with an import statement. For example, if you want to include beep into the comment example "root" from above, you can add import "beep" and include a state that references beep.

import "beep"

/**
 * Getting there!
 */
scchart Root {
	/** Test */
	input bool second 
	output bool speaker 
	
	/**
 	 * Main region!
     */
	region main:
	
	/**	
	 * The initial state
	 * This is entered as soon as the program starts.
	 * @foreground f0f024
	 * @background ffffcc
     * @backgroundTarget fff9ba
	 */    
	initial state R is Beep(second to second, speaker to beep) 
	/** Transition */
	/** Transition 2 */
	join to S
	
	/**
	 * The final state!
	 * @foreground f0f0240
     * @background ffc
     */
	final state S
}

The keyword is indicates that R is a reference. When you are referencing, you have to bind the interface of the referenced SCChart model to variables of the actual on. You must do this in the parentheses after the referenced state. In the example second is bound to second, and the local speaker boolean is bound to the beep from beep's interface. You can read more about variable bindings in the next paragraph. Also, the content assist will help you with your bindings and inform you about missing bindings.

Details about Bindings

There are three different kinds of bindings: explicit bindings, order bindings, and implicit bindings. In the example we used explicit bindings, which are the safest way of bindings.

initial state R is Beep(second to second, speaker to beep) 

They state explicitly which local variable gets bound to which remote. The content assist will help you with errors.

If you know the order of the variables (and/or listen to the content assist), you can also use order bindings and simply state the list of local variables.

initial state R is Beep(second, speaker) 

They will be bound to the interface in the order of declaration in the remote SCChart. However, be aware of the fact that the bindings will change, when the declarations of the referenced SCChart change.

In the example, the names of the local and referenced second variables are identical. Hence, you can also omit the binding completely.

initial state R is Beep(speaker to beep) 

SCCharts will then bind the variable implicitly. However, we also consider this kind of binding unsafe and the editor will warn you about any implicit bindings. They can be handy though when dealing with large interfaces.

Continuation

As any state, referenced states are allowed to own transitions. However, if you are using terminations, you must make sure that the referenced SCChart terminates. Otherwise, the transition will never trigger. The content assist will help you with this issue.

Legacy

You do not need to activate the Xtext nature as in previous versions of SCCharts. In fact, we recommend to deactivate the Xtext nature for SCCharts projects.



Example warnings from the content assist:


Inheritance

SCCharts support inheritance, similar to the concept of references.

Each root state can extend multiple base states (since the name super states is already used) by listing them after the extends keyword.

Such an state will inherit all declarations, action and regions of the base states. If conflicts arise or a state has a cyclic inheritance hierarchy, a warning will be displayed. If a state is contained multiple times in the inheritance hierarchy its content will inherited only once.

Declarations can have the private keyword to prevent extending SCCharts from accessing these variables.

Root-level regions of base states can be overriden with the override keyword and consequently replace the behavior by the new definition. Anonymous regions (defined without an ID) cannot be overridden.

Regions can also be references similar to states by using the is keyword. If the reference should refer to the implementation in the base state, the super keyword must be used.

scchart MotorWithButton
  extends ButtonBehavior, MotorBehavior {
    
  override region HandleMotor {
    suspend if !buttonPressed
    
    region is super.HandleMotor
  }
}

scchart MotorBehavior {
  output int motorRotation
  
  const int motorRotationMax = 16
  entry do motorRotation = 0
  
  region HandleMotor {
    initial state Increment {
      during do motorRotation++
    } if motorRotation == motorRotationMax
      do motorRotation = 0
      abort to Increment
  }
}

scchart ButtonBehavior {
  input float buttonPosition
  
  bool buttonPressed = false
  private const float threshold = 0.5
  
  region HandleButton {
    initial state Released
      if buttonPosition < threshold
      do buttonPressed = true
      go to Pressed
    
    state Pressed
      if buttonPosition >= threshold
      do buttonPressed = false
      go to Released
  }
}

Dataflow

You can convert a region into a dataflow region by replacing the region keyword with the keyword dataflow. Within a dataflow scope, you can simply write down your equations.

On the right you see several examples and their synthesized diagrams.

Equations (df#0007)

You can use all expressions in the kexpressions language. This includes standard operations such as arithmetics and binary/logical logic. A full set of operations can be found at the end of this page (in the future).

References (df#0461)

Just as before, you can declare references to other SCCharts. As before, use the ref keyword in your declaration section. Each variable represents an instance. Inputs and outputs are separated by a dot (.). Same wires are merged automatically in the diagram.

Input/Output Loops (df#0521)

Of course you can model loops in your wiring. However, depending on the consecutive compilation/scheduling the program may or may not be executable/schedulable.

Tuples (df#0603)

You can use the aforementioned tuple syntax to assign all/some inputs at once. Hence, it is possible to construct complex models with only a few lines of code.

Skins (df#1000, df#1100)

You can use customized skins instead of the standard referenced SCCharts actor diagram. Since we are using Klighd, you have to specify your actor in Klighd's Graph Syntax (.kgt). Once you have created a custom .kgt, you can add it to an SCChart with the @figure annotation. The annotation combined with a skinpath relative to the calling model points to the target .kgt.

For example: Imaging df#0007 is annotated with @figure "and2AN.kgt". Now df#1000 can set a skinpath pragma. Together they point to the .kgt that should be used as actor diagram. In this case, we get an and with a negated input.

Even if df#0007 was not annotated, you can archive the same result if you annotate the ref declaration in df#1000.:

  @figure "and2AN.kgt" 
  ref df#0008 A, A2
scchart df#0007 {
  input bool in1, in2
  output bool out
	
  dataflow:
  out = in1 + in2
}
import "DF-0002"

scchart df#0461 {
  output int O, O2, O3, O4
  ref df#0002 A, A2, A3, A4

  dataflow:
  O = A.O || A2.O || A3.O 
  O2 = A.O || A2.O || A3.O 
  O3 = A.O || A2.O || A3.O 
  O4 = A.O || A2.O || A3.O 
}
import "DF-0000"

scchart df#0521 {
  input bool I
  output int O
  ref df#0000 A

  dataflow:
  A.I = I + A.O
  O = A.O
}
import "DF-0006"

scchart df#0603 {
  input int I, I2
  output int O
  ref df#0006 A, A2

  dataflow:
  A = {0, 1, _, I}
  A2 = {0, A.O, I + 1, I - 1}
  A.I3 = 100
  O = A2.O
}
import "DF-0007"
#skinpath "skin"

scchart df#1000 {
  input int I, I2
  output int O
  ref df#0007 A, A2

  dataflow:
  A = {true, false}
  A2 = {true, A.out}
  O = A2.out
}

Hostcode

There are several ways to add hostcode to your models.

External References (hostcode#10)

You can declare a new object as external reference like before with (internal) references. Use the keyword extern to mark it as extern. Then use a string to set the name of the function and an object which you will use to reference this hostcode snippet. As it is handled as a call, you can add parameters and they will be recognized by the dependency analysis.

Additionally, you can annotate your code snippets with the name of the code generator (e.g. C, Java) to tell the code generation which one should be used when. See the example on the right for more details.

Function Calls

While an External Reference is the preferred way to declare a hostcode call, you can call any function without declaring it first. However, due to grammar limitations and platform-dependency this older features is considered deprecated. You should really use external references. 

Nevertheless, you can still use this feature by using the extern keyword directly inside the expression (e.g. r = extern gettimeofday()) without declaring the call beforehand. 

The dependency analysis will consider parameters.

Legacy Hostcode (hostcode#30)

You can simply place the host code in accent grave (`) quotes. The code is put as it is into the final code. There is no further processing and also no parameter list. You can of course put the parameters inside the host code quotes, but they will be copied as they are.

scchart hostcode#10 {
  output float r
  extern @C "rand", 
         @Java "Math.random" 	rand
	
    entry do rand(0)
		
    initial state init 
    do r = rand() go to init
}
scchart hostcode#30 {
	entry do `srand();`
	
	initial state init
}




Annotations

The textual SCCharts language supports several annotations to influence the visual representation of the model.

Annotation are processed in sequential order.

PatternUsageDescriptionExample
@diagram[<key>] <value>
Location:scchart
<key>The name of the synthesis option. The given name is evaluated case-insensitive and whitespace-ignoring. The options are searched for the first matching prefix.
<value>

The value type depends on the option type:

CheckBox: true or false

Choice: Name of choice item

Slider: Float value

Sets the synthesis option identified by <key> to the given value.

The available synthesis options for a diagram are displayed in the sidebar of the diagram view.

The values from the sidebar will be ignored if a corresponding annotation is present.

 Commonly Used
initiallycollapseregions
Collapses all regions. Very helpful for lager models, since it fastens initial diagram rendering.



@diagram[paper] true
scchart Testing {
  initial state A
  --> B;
  final state B;
}
@layout[<key>] <value>
Location:scchart, state, region, transition
<key>The ID of the layout option. The options are searched for the first matching postfix.
<value>

The value type depends on the option type. The value is parsed case-sensitive.

Sets the layout property identified by <key> to the given value on the annotated element.

The available layout options are documented here.

Layout options will only affect the annotated element and no underlying hierarchy levels.

If a layout direction is specified with this annotation it overrides the layout direction set by HV-/VH-Layout in any parent element for this element.

Special case: If the direction is set on the scchart element (top level) it overrides the default alternating layout.

The layout option is identified by matching a postfix. Hence the key direction matches both org.eclipse.elk.direction and org.eclipse.elk.layered.priority.direction.
If none or multiple options match a warning is displayed.

 Commonly Used
elk.direction
Layout direction
elk.priorityInfluences the order of regions
scchart Testing {
    @layout[algorithm] org.eclipse.elk.graphviz.circo
    region:
    initial final state A
    --> B;
    state B
    --> C;
    state C
    --> A;
}



scchart Testing {
    @layout[elk.direction] UP
    region "up":
    initial state A
    --> B;
    final state B;
    @layout[elk.direction] LEFT
    region "left":
    initial state A
    --> B;
    final state B;
}



@HVLayout
@VHLayout
Location:scchart, state, region

Defines the order of the alternating layout directions.

The annotation can be mixed and nested in the SCChart and will only affect succeeding hierarchy levels.

The default is an implicit HVLayout starting at the top level state.

@VHLayout
scchart Testing {
  initial state A
    go to B;
  final state B;
}
@collapse
@expand
Location:region
The annotated region will be initially collapse or expanded.
scchart Testing {
  @collapse  
  region {
    initial state A
      go to B;
    final state B;
  }
}
@hide
Location:scchart, state, region, transition

The annotated element will be excluded from the diagram.

Transitions with a hidden source or target state will be hidden as well.

scchart Testing {
  initial state A
    go to B;
  @hide
  final state B;
}

Pragmas

Pragmas are annotations that are valid for the whole file in contrast to annotations that are valid for semantic model elements. They are placed in front of an .sctx.

PragmaEffect
#KiCoEnv {<json>}Configures the compiler environment.
#hostcodeAllows hostcode additions that are placed at the beginning of the generated code file. The exact handling may depend on the used code generator.




Quick Overview

Here you can see an SCCharts graphical notation overview.



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1 Comment

  1. Some feedback regarding the experimental syntax for transitions:

    I vastly prefer the suggested version with the `if` first, followed by the actions and the target last.

    The only thing I can't place right on the first try is the history keyword. I always try to place it before the `go to`.