etl/docs/state machines/hierarchical-finite-state-machine.md

title
Hierarchical Finite State Machine

{{< callout type="info">}} Header: hfsm.h
Since: 20.10.0 {{< /callout >}}

Hierarchical Finite State Machine

The ETL's etl::hfsm is derived from etl::fsm and utilises the same state template classes.
See etl::fsm

Note:
For an etl::hfsm, on_enter_state() cannot force a state change. It must return etl::ifsm_state::No_State_Change.
If it does not, then an ETL_ASSERT will be raised.

Defines etl::hfsm plus all defined in fsm.h.

hfsm

The state machine.
Inherits from etl::fsm.

hfsm(etl::message_router_id_t id)

Constructor.
Sets the router id for the HFSM.
The HFSM is not started.

void receive(const etl::imessage& message)

Top level message handler for the HFSM.

Errors

Additional errors to etl::fsm.

fsm_state_composite_state_change_forbidden

Inherits from etl::fsm_exception

Example

The states

Idle        idle;
Running     running;
WindingUp   windingUp;
WindingDown windingDown;
AtSpeed     atSpeed;

struct StateId
{
  enum
  {
    Idle,
    Running,
    Winding_Up,
    Winding_Down,
    At_Speed,
    Number_Of_States
  };
}

struct EventId
{
  enum
  {
    Start,
    Stop,
    EStop,
    Stopped,
    Set_Speed,
    Timeout
  };
};

// These are all of the states for this HSFM.
etl::ifsm_state* stateList[StateId::Number_Of_States] =
{
  &idle, &running, &windingUp, &windingDown, &atSpeed
};

// These states are child states of 'Running'.
etl::ifsm_state* childStates[] =
{
  &windingUp, &atSpeed, &windingDown
};

MotorControl motorControl;

running.set_child_states(childStates, etl::size(childStates));

motorControl.Initialise(stateList, etl::size(stateList));