Stateflow    

Transitions to and from Exclusive (OR) States

Example: Processing of One Event

This example shows the semantics of a simple transition focusing on the implications of states being active or inactive.

Initially the Stateflow diagram is asleep. State On and state Off are OR states. State On is active. Event E_one occurs and awakens the Stateflow diagram. Event E_one is processed from the root of the Stateflow diagram down through the hierarchy of the Stateflow diagram:

  1. The Stateflow diagram root checks to see if there is a valid transition as a result of E_one. A valid transition from state On to state Off is detected.
  2. State On exit actions execute and complete (ExitOn()).
  3. State On is marked inactive.
  4. The event E_one is broadcast as the transition action. The second generation of event E_one is processed but because neither state is active, it has no effect. (Had a valid transition been possible as a result of the broadcast of E_one, the processing of the first broadcast of E_one would be preempted by the second broadcast of E_one.)
  5. State Off is marked active.
  6. State Off entry actions execute and complete (entOff()).
  7. The Stateflow diagram goes back to sleep waiting to be awakened by another event.

This sequence completes the execution of the Stateflow diagram associated with event E_one when state On was active.

Example: Processing of a Second Event

Using the same example, what happens when the next event, E_one, occurs?

Again, initially the Stateflow diagram is asleep. State Off is active. Event E_one occurs and awakens the Stateflow diagram. Event E_one is processed from the root of the Stateflow diagram down through the hierarchy of the Stateflow diagram:

  1. The Stateflow diagram root checks to see if there is a valid transition as a result of E_one. A valid transition from state Off to state On is detected.
  2. State Off exit actions execute and complete (exitOff()).
  3. State Off is marked inactive.
  4. State On is marked active.
  5. State On entry actions execute and complete (entOn()).
  6. The Stateflow diagram goes back to sleep waiting to be awakened by another event.

This sequence completes the execution of the Stateflow diagram associated with the second event E_one when state Off was active.

Example: Processing of a Third Event

Using the same example, what happens when a third event, E_two, occurs?

Again, initially the Stateflow diagram is asleep. State On is active. Event E_two occurs and awakens the Stateflow diagram. Event E_two is processed from the root of the Stateflow diagram down through the hierarchy of the Stateflow diagram:

  1. The Stateflow diagram root checks to see if there is a valid transition as a result of E_two. There is none.
  2. State On during actions execute and complete (durOn()).
  3. The Stateflow diagram goes back to sleep waiting to be awakened by another event.

This sequence completes the execution of the Stateflow diagram associated with event E_two when State On was active.

Example: Transition from a Substate to a Substate

This example shows the semantics of a transition from an OR substate to an OR substate

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Initially the Stateflow diagram is asleep. State A.A1 is active. Event E_one occurs and awakens the Stateflow diagram. Condition C_one is true. Event E_one is processed from the root of the Stateflow diagram down through the hierarchy of the Stateflow diagram:

  1. The Stateflow diagram root checks to see if there is a valid transition as a result of E_one. There is a valid transition from state A.A1 to state B.B1. (Condition C_one is true.)
  2. State A executes and completes during actions (durA()).
  3. State A.A1 executes and completes exit actions (exitA1()).
  4. State A.A1 is marked inactive.
  5. State A executes and completes exit actions (exitA()).
  6. State A is marked inactive.
  7. The transition action, A, is executed and completed.
  8. State B is marked active.
  9. State B executes and completes entry actions (entB()).
  10. State B.B1 is marked active.
  11. State B.B1 executes and completes entry actions (entB1()).
  12. The Stateflow diagram goes back to sleep waiting to be awakened by another event.

This sequence completes the execution of this Stateflow diagram associated with event E_one.


 Semantics of Transitions Condition Actions