Agenda

1. Using VisSim State ChartsVisual Solutions, Inc.487 Groton Road, Westford MA 01886 USA(800) VISSIM-1www.vissim.com

2. Agenda • Creating State Charts • Hierarchy • Transitions • Debugging/Logging • Embedded Considerations

3. What is a State Chart? • A graphical representation of a finite-state machine • A system with a fixed number of named states. Transitions between states occur when certain conditions are met. • VisSim State Charts are OMG UML 2.1 conformant • Create state charts anywhere in a VisSim diagram • Exchange data between the state chart and the continuous portion of a diagram • Use VisSim variables or Triggers in chart, as well as defined input and output pins

4. Example State Chart

5. Basic state chart elements • States – set of named system configurations • Transitions - control movement between states • Pseudo states – Alter transition operation • Behaviors- code associated with transitions and state events • Triggers – named events that can cause transitions or code to be executed

6. Creating a State Chart • Insert a State Chart block into a VisSim diagram. • Right click drills down and enters State Chart world • Notice normal VisSim blocks are disabled and State Chart elements are enabled • Insert an Initial State and two states

7. Creating Transitions • 1. Position the cursor over the edge of a source state. The cursor shape changes to a pencil • If the cursor is a crosshair with arrow heads, moving the mouse moves the state rather than draws the arc. • 2. Depress the mouse and drag into the target state body. • If the state is a composite state, you may connect to a state within the composite state. • 3. Release the mouse button.

8. Moving Transitions • Click the mouse over a transition you want to bend or move. • The transition line turns purple, indicating that you can edit it. • To bend the transition, left click on it and drag the mouse. • Labels will move with the arc • To move where the transition arc connects to a state edge, position the cursor over the end of the arc you want to move. • When the cursor changes to a 4-arrow crosshair, depress and drag the mouse to the desired location.

9. Controlling Transitions • You can use triggers and C expressions to control if and when transitions are taken • Double click on Transition to edit • Transitionsyntax: trigger(s) [guard] / C-code • Guard is C expression • Triggers and guard are optional, but ‘/’ is not • All triggers and guard must be true to execute transition and C-code

10. Triggers • Triggers are True or False • Declare in Continuous space via Trigger Block • or Data Browser (type = Trigger) • Assign value in continuous space • Like VisSim variables only one definition point • or State Chart Action via SendT(<trigname>) • Reference in State Chart Transitions and Actions.

11. Deferred Triggers • If you defer a Trigger in a state, the state will remember any True setting and hold it for one tick after the state is exited. • This makes it available for an action in the next state transitioned to for 1 tick. • defer a trigger by adding to Deferred Triggers list in State Activity Manager

12. Transition Evaluation Order • Multiple output transitions have an evaluation order indicated by number near start of arc • To change, right click transition, select “Reorder Transitions” • Click transitions in order of desired execution • Transitions with no trigger are always evaluated after transitions with trigger (regardless of order number) • At most one transition fires per Chart Region during one simulation or codegen timer tick.

13. Defining state chart variables • To exchange data between the VisSim model and the state chart, use variables. • State chart variables are declared in the State Chart Block Properties • Activate View > Connector Labels to see the pin names • To define input and output variables: • Add Connector command (or toolbar button) • Or ctrl+right click the state chart block and click Data Browser. Data Browser gives you ability to choose name, data type and storage for each variable

14. Data Browser • Click (new item icon) to create new variable • Type • char .. double = data type as in C • Trigger = Boolean (True or False) • State ID = currently active state • Scope • Local = only seen within State Chart • Input/output = input/output pins • Constant = constant value • External = Seen outside State Chart

15. Data Browser (cont.) • Pin – assigned to inputs and outputs • Default value – initial value before 1st assignment • Value – current value • Comment – whatever you like • To edit a variable, double click the property

16. Configuring States • Right click in State title bar to open properties • Options tab gives name and comment fields and shows some activity code (not editable) • Activity Manager Tab lets you associate C-code to be called on certain events (actions) • Entry – on State entry • Exit – on State exit • Do – while in State • On trigger – when in State and trigger is True

17. Allowable C-code in Activity • ANSI C expressions, statements and functions are OK. • Can put initial C file in Sim Properties> Preferences > startup script file • Standard library math functions (pow, abs, exp, min, max etc) • No preprocessor commands supported (#define, #if, #else)

18. Creating Actions • Click on the action or trigger you wish to activate C-code then click “Add Action” • Code is inserted in “Edit Behavior” and may be edited further. • Action code syntax • {action name}/{C-code} i.e. Entry / startup = 1;

19. Controlling State Chart Execution • Initial State - indicates starting point for State Chart, Submachines and Composite States • Terminate - indicates final state end point. • Exits from Submachine or Composite region • Choice – expression selects destination state • Fork – Notational convenience for entering multiple regions in Composite State • Join– Notational convenience for leaving multiple regions in Composite State

20. Transition Choice if (A) { /* exit State One*/ B; if (C) {D; /*Enter State Two*/ } else if (E){ F; /*Enter State Three*/ } } • It is a FATAL ERROR to enter a choice but not take exit leg to a state. • Only place State Charts can halt besides Terminate

21. To avoid Choice FATAL ERROR • Always have one exit leg with no predicate • Check Integrity will check for this. • Don’t use Choice, use Join with predicates. That way, current state will never be left unless possible path exists.

22. Interacting with State Charts • To send data from the continuous portion to a State Chart you can use: • State Chart input/output pins • VisSim variables • Triggers • To read the current state in the continuous portion • Use an output pin set to State ID • Use a state id block.

23. Controlling VisSim execution • Use state id block “is active” mode • Test “State Id” output pin of state against state id block in “State Id” mode. • State ID values are unique but can change. Don’t depend on actual value. Values change between simulation and code generation and as states are added and removed. • Can use merge to select data or enabled Compound block to control execution

24. Hierarchical States • You can encapsulate a state chart within a state chart by using a Submachine state. • Enter a Submachine by double click on title bar • You can use Initial State or Terminate to enter and exit, or • Use Entry and Exit points for different initial and final states. • Entry and exits are placed inside the Submachine and will automatically appear on Submachine face

25. Parallel State Execution Regions • Use Composite State for multiple active states • Right click in Composite body, select insert vertical/horizontal region to create new region • To delete region, drag dashed line off screen. • Use Initial State to indicate first state in region • Use Terminate State to end region. When all regions are done, can leave Composite State • Can transition directly from state in region to state outside Composite State • Other regions active states are ended immediately

26. History • If you transition directly out of a Composite Region without termination of other regions, and a history element is present, the history element will remember currently active states. • If you renter Composite Region via History, prior active state(s) will be entered. • See examples ShallowHistory001&002

27. Deep History vs Shallow • Shallow history only remembers active state(s) on current layer of Composite or Submachine. • Deep history remembers all active states in all nested Composite and Submachines.

28. Debugging State Charts • You can set break points or log action for any action in any state or transition • Right click to open properties, click on action, and check “Attach Breakpoint” (red ball appears) or “Log Message” (red exclamation appears) • When sim is run and action occurs, sim will stop at time step for breakpoint. Data Browser contains current data values.

29. VisSim Error Reporting • The menu item “Check Integrity” will scan and report on ill-formed charts. • Click error, then use arrow and hand to jump to state in error • “Check Integrity”is also run when you click “Go” • States with errors are highlighted.

30. Breakpoints • Menu item State Charts > Breakpoints… • Shows list of Breakpoints and Log points • Can remove one or more BPs • Can jump to next occurance of BP

31. Logging Actions • To log actions, right click state or transition to open properties, click on action, and “Log Message” (red exclamation appears on state, red ball on transition) • Place identifing text in the edit box to the right of “Log Message” to be entered into the event log • To see the events in the log, leave the state chart and place an standard VisSim Block > Signal Consumer > Event Display block into the workspace. • When the simulation is run, time stamped events will appear in the event log.

32. Logging C-code execution • To enable C-code logging, Ctrl-Right Click on the enclosing State Chart and enable "Log executed C instructions“, then press Ok • Run the diagram • Ctrl-Right Click on the chart again and click “Open”

33. Embedded Considerations • Compiled State Chart should work the same as simulated, so simulate as much as you can • Compiled States IDs may be different numerical values than simulated. • State Lookup… menu item has “embedded” option • sim ID->embedded ID convert block in works • For low freq state change, use State ID from Data Browser as output from top level compound. • For high freq state change use Monitor Buffer Write

34. Embedded Operations to Avoid • Terminate – halts operation • Choice without Else

35. Q&A