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SCCharts are typically modeled using the textual SCT language defined as an Xtext grammar in KIELER. Generally, if you do not know which elements can be placed at a certain cursor position you are assisted by a content-assist that can be called pressing <Ctrl>+<Space>. It will display all possible valid elements also considering scoping of variables.

In the following we will demonstrate SCT using the famous ABRO example (the hello world of synchronous programming/modelling). We will then give details for modelling other SCCharts language constructs with SCT. For details on their semantics please be referred to to  our PLDI paper [1].

ABRO Example

In the following we will describe the basic elements using the famous ABRO example:

[1] R. von Hanxleden, B. Duderstadt, C. Motika, S. Smyth, M. Mendler, J. Aguado, S. Mercer, and O. O’Brien. SCCharts: Sequentially Constructive Statecharts for Safety-Critical Applications. In Proc. ACM SIGPLAN Conference on Programming Language Design and Implementation (PLDI’14), Edinburgh, UK, June 2014. (pdf)

ABRO Example

In the following we will describe some basic elements using the famous ABRO example:

@HVLayout
scchart ABRO {
  input bool A;
  input bool B;
  input bool , B, R;
  output bool O = false; 
  region Main:
  initial state ABO "ABthenO" {
    entry initial/ stateO WaitAB= {false;
    initial state WaitAandB {
      region HandleA: 
      initial state WAwA 
      --> DAdA with A;
      final state DAdA;
      region HandleB:
      initial state WBwB
      --> DBdB with B;
      final state DBdB;
    }
    >-> Donedone with / O = true;
    final state Donedone;
  }
  o-> ABO with R;
}            

1. In the first line you see how an SCChart is defined using the scchart keyword where the ID of the SCChart will be ABRO. An optional label can be inserted after ABRO using "<LABEL>".
2. In the next three lines variables are declared, namely, A, B, R and O, where O is initialized with the value false. A, B, and R are inputs which must not be initialized and get there valued from the environment.
3. An SCChart typically contains concurrent regions which are introduced with the keyword region as shown in Line 69.
4. Every region must at least have one state, and every region must exactly have one initial state. An initial state ABO is defined for region Main in Line 76.
5. Every state is terminated by a ; as shown in line 11 for state HandleA.
6. If you like to specify internal behavior of a state, you can add concurrent regions to a state in { <regions> } as done for state ABO or state WaitAB.
7. Transitions outgoing from a state must be declared right before a state is terminated with ;. For example a transition from state WA wA to state DA dA is declared in Line 11.
8. Transitions can have triggers and effects which are separated by a dash: <trigger>/<effects>. Multiple sequential effects are separated by a ;. The transition in Line 11 declares just a trigger A (a dash is not necessary in this case), while the transition from line 18 declares only an effect O = true (here the dash is mandatory).
9. There are three types of transitions: 1. normal/weak abort transitions -->,  2. strong abort transitions o-> and 3. termination/join transitions >->.

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Detailed SCT Syntax of SCCharts

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Elements

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SCChart, Initial State, State, Transition and Immediate Transition

 scchart StateTransition {
  initial state A
  --> B;
  state B
  --> C;
  state C
  --> A immediate;
}

Variable

scchart Variable {
  int var1;
  bool var2;
  int var3 = 3;
  bool var4 = false;
  input int var5;
  output float var6;
  input output bool var7;
  initial state A
  --> B;
  state B;
}

Transition: Trigger & Effect

scchart TriggerEffect {
  input int var1;
  output bool var2;
  initial state A
  --> B with var1 == 3 / var2 = true;
  state B;
}

Super State

scchart SuperState {
  initial state A
  --> B;
  state B {
    initial state B1
    --> B2;
    state B2;
  };
}

Super State: Final States & Termination Transition

scchart FinalStateTermination {
  initial state A
  --> B;
  state B {
    initial state B1
    --> B2;
    final state B2;
  }
  >-> C;
  state C;
}

Super State: Weak Abort Transition

scchart WeakAbort {
  input bool W;
  initial state A
  --> B;
  state B {
    initial state B1
    --> B2;
    state B2;
  }
  --> C with W;
  state C;
}

Super State: Strong Abort Transition

scchart StrongAbort {
  input bool S;
  initial state A
  --> B;
  state B {
    initial state B1
    --> B2;
    state B2;
  }
  o-> C with S;
  
  state C;
}

Concurrent Regions (inside a Super State)

scchart Regions {
  input bool S;
  initial state A
  --> B;
  state B {
    region Region1 :
    initial state B1
    --> B2;
    state B2; region Region2 :
    initial state B3;
  };
}

Entry Action, During Action, Exit Action

scchart Actions {
  input bool var1;
  output bool var2;
  initial state A
  --> B;
  state B {
    entry var1 / var2 = true;
    during var1 / var2 = true;
    immediate during var1 / var2 = true;
    exit var1 / var2 = true;
    initial state B1
    --> B2;
    state B2;
  };
}

Shallow History Transition

scchart HistoryShallow {
  input bool var1;
  output bool var2;
  initial state A
  --> B shallow history with var1;
  state B {
    initial state B1
    --> B2;
    state B2;
  }
  --> A with var1;
}

Deep History Transition

scchart HistoryDeep {
  input bool var1;
  output bool var2;
  initial state A
  --> B history with var1;
  state B {
    initial state B1
    --> B2;
    state B2;
  }
  --> A with var1;
}

Deferred Transition

scchart Deferred {
  input bool var1;
  output bool var2;
  initial state A
  --> B deferred with var1;
  state B {
    entry var1 / var2 = true;
  }
  --> A with var1;
}

Transition with Count Delay

scchart CountDelay {
  input bool var1;
  output bool var2;
  initial state A
  --> B with 4 var1;
  state B
  --> A with var1;
}

Array

scchart Array {
  int myArray[10][2];
    initial state init
  --> done with myArray[1][0] == 1 / myArray[2][1] = 2;
  final state done;
} 

Signal

scchart Signal {
  input signal i;
  output signal o
    initial state init
  --> done with i / o;
  final state done;
}  

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Array

scchart Array {
  int myArray[10][2];
    initial state init
  --> done with myArray[1][0] == 1 / myArray[2][1] = 2;
  final state done;
} 

Signal

scchart Signal {
  input signal i;
  output signal o
    initial state init
  --> done with i / o;
  final state done;
}  

Reference States

Important: To use the referenced SCCharts feature, activate the Xtext nature for your project!

scchart MainSCChart {
  bool A[3];
  
  initial state S1 references InnerSCChart; 
}

scchart InnerSCChart  {
  input bool A[3];
  
  initial state S1
  --> S2 with A[0];
  
  final state S2;
} 

Hostcode

You can also use you host language directly.

Function Calls

Call host code functions with dependency analysis. Use angle brackets to point to an extern function. You can also declare extern variables.

@hostcode "#include <stdio.h>"
@hostcode "#include <stdlib.h>"
scchart functionCall {
  output int i;
  extern int stdout;
  
  initial state getChar {
    entry / <printf("Enter an integer: ")>;
    entry / <fflush( stdout )>;
    entry / <scanf("%d", &i)>;
  }
  --> print with / <printf("The interger you entered: %d\\n", i)>; 
  				   <fflush( stdout )>;
  
  state print 
  --> getChar;
} 

Hostcode (inline)

Inline hostcode just as it is. Use the @hostcode annotation to add hostcode line before the tick function. Also use hostcode in single quotes as hostcode effects.

Important: Inline hostcode is not type-safe. Be careful.

@hostcode "#include <stdio.h>"
@hostcode "#include <stdlib.h>"
@hostcode "#include <unistd.h>"
@hostcode "#include <sys/time.h>"
@hostcode "struct timeval val;"
scchart hostcode {
  output int ms;
  
  initial state getChar {
    entry / 'gettimeofday(&val, NULL)'; 
    		ms = 'val.tv_sec'
  }
  --> print with / 'printf("Second: %d\\n", ms); fflush( stdout )';
  
  state print 
  --> getChar;
}

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Annotations

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

Annotation are processed in sequential order.

@diagram[<key>] <value>

@diagram[paper] true
scchart Testing {
  initial state A
  --> B;
  final state B;
}

@layout[<key>] <value>

direction

scchart Testing {
    @layout[algorithm] de.cau.cs.kieler.graphviz.circo
    region:
    initial final state A
    --> B;
    state B
    --> C;
    state C
    --> A;
}

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

@HVLayout
@VHLayout

@VHLayout
scchart Testing {
  initial state A
  --> B;
  final state B;
}

@collapse
@expand

scchart Testing {
  @collapse  
  region:
  initial state A
  --> B;
  final state B;
}

@hide

scchart Testing {
  initial state A
  --> B;
  @hide
  final state B;
}

Overview of Operators

The following briefly describes the operators that can be used in expressions.

Increment