Tutorial 10 — Multi-Stage Missions

This tutorial brings together everything you have learned to study two complete multi-stage state machines: sm_multi_stage_1 (a complex hierarchical demo) and sm_cl_px4_mr_test_1 (a real-world PX4 flight mission).

sm_multi_stage_1: Architecture

sm_multi_stage_1 demonstrates the largest SMACC2 hierarchical pattern:

SmMultiStage1
├── MsMode1
│   ├── SequenceA (loop: StiLoop → Sti1 → Sti2 → ... → Sti9)
│   ├── SequenceB
│   ├── SequenceC
│   └── SequenceD → EvLoopEnd → MsMode2
├── MsMode2
│   ├── SequenceA → SequenceB → SequenceC → SequenceD → MsMode3
├── MsMode3
│   └── ... → MsMode4
├── MsMode4
│   └── ... → MsMode5
├── MsMode5
│   └── ... (terminal or loop back)
├── MsRecovery1
│   └── Recovery sequences → MsMode::deep_history
└── MsRecovery2
    └── Recovery sequences → MsMode::deep_history

Key patterns:

  • 5 operational modes with multiple sequences each

  • Recovery modes that restore the previous state via deep history

  • Sequence super states with inner loop states (each sequence loops through 9 steps)

  • Mode-to-mode transitions via EvLoopEnd<SequenceD>

Mode State Transitions

struct MsMode1 : smacc2::SmaccState<MsMode1, SmMultiStage1, SequenceA>
{
  using SmaccState::SmaccState;

  typedef mpl::list<
    Transition<EvLoopEnd<SequenceD>, MsMode2>
    >reactions;
};

When SequenceD inside MsMode1 finishes its loop iterations, it posts EvLoopEnd<SequenceD>. The mode state catches this and transitions to MsMode2.

sm_cl_px4_mr_test_1: Real-World Mission

This state machine flies a PX4 multirotor through a complete mission: arm → takeoff → navigate → orbit → return → land.

State Machine Definition

// sm_cl_px4_mr_test_1.hpp
struct SmClPx4MrTest1
  : public smacc2::SmaccStateMachineBase<SmClPx4MrTest1, MsDisarmedOnGround>
{
  using SmaccStateMachineBase::SmaccStateMachineBase;

  virtual void onInitialize() override
  {
    this->createOrthogonal<OrPx4>();
    this->createOrthogonal<OrTimer>();
  }
};

Mode States

The mission is organized into 6 flight phases, each a mode state:

Mode State

Initial Child

Purpose

MsDisarmedOnGround

StWaitForReady

Wait for PX4 topics

MsArmedOnGround

StArmPx4

Arm the vehicle

MsTakeoff

StTakeoff

Climb to target altitude

MsInFlight

StGoToWaypoint1

Execute mission waypoints

MsLanding

StLand

Descend and touch down

MsLanded

(terminal)

Mission complete

Mission Flow

MsDisarmedOnGround
  └── StWaitForReady ──[EvTimer]──→ MsArmedOnGround
        └── StArmPx4 ──[EvCbSuccess]──→ MsTakeoff
              └── StTakeoff(5.0m) ──[EvCbSuccess]──→ MsInFlight
                    ├── StGoToWaypoint1(10,0,-5) ──[EvCbSuccess]──→
                    ├── StOrbitLocation(r=5,n=3) ──[EvCbSuccess]──→
                    └── StReturnToBase(0,0,-5) ──[EvCbSuccess]──→ MsLanding
                          └── StLand ──[EvCbSuccess]──→ MsLanded

Each state uses a single behavior that posts EvCbSuccess on completion:

// states/in_flight/st_go_to_waypoint_1.hpp
struct StGoToWaypoint1 : smacc2::SmaccState<StGoToWaypoint1, MsInFlight>
{
  using SmaccState::SmaccState;

  typedef mpl::list<
    Transition<EvCbSuccess<CbGoToLocation, OrPx4>, StOrbitLocation, SUCCESS>
    >reactions;

  static void staticConfigure()
  {
    // NED coordinates: 10m North, 0m East, 5m altitude (negative Z = up)
    configure_orthogonal<OrPx4, CbGoToLocation>(10.0f, 0.0f, -5.0f);
  }
};

// states/in_flight/st_orbit_location.hpp
struct StOrbitLocation : smacc2::SmaccState<StOrbitLocation, MsInFlight>
{
  using SmaccState::SmaccState;

  typedef mpl::list<
    Transition<EvCbSuccess<CbOrbitLocation, OrPx4>, StReturnToBase, SUCCESS>
    >reactions;

  static void staticConfigure()
  {
    // center=(10,0), alt=5m, radius=5m, angular_vel=0.5 rad/s, 3 orbits
    configure_orthogonal<OrPx4, CbOrbitLocation>(
      10.0f, 0.0f, 5.0f, 5.0f, 0.5f, 3);
  }
};

Signal Wiring End-to-End

The complete chain from state configuration to event:

  1. State calls configure_orthogonal<OrPx4, CbGoToLocation>(10.0f, 0.0f, -5.0f)

  2. CbGoToLocation::onEntry() calls requiresComponent(goalChecker_) and requiresComponent(trajectorySetpoint_)

  3. CbGoToLocation sets the goal on CpGoalChecker and the setpoint on CpTrajectorySetpoint

  4. CpGoalChecker::update() (called at 20 Hz) compares current position vs goal

  5. When within tolerance, CpGoalChecker fires onGoalReached_ signal

  6. CbGoToLocation::onGoalReachedCallback() calls postSuccessEvent()

  7. EvCbSuccess<CbGoToLocation, OrPx4> matches the transition → next state

Cross-Orthogonal Access

Sometimes a behavior needs data from a component on a different orthogonal. You can access any orthogonal’s client and components through the state machine:

void onEntry() override
{
  // Access a component from a different orthogonal
  auto * otherClient = this->getStateMachine()
    ->getOrthogonal<OrOther>()
    ->getClient<ClOtherClient>();

  ClOtherComponent * comp;
  otherClient->requiresComponent(comp);
}

Designing Your Own Multi-Stage Mission

When designing a complex mission:

  1. Identify the major phases — these become mode states (e.g., Initialization, Active, Recovery, Shutdown)

  2. Break each phase into steps — these become states within the mode state

  3. Identify repeating patterns — these become super state loops

  4. Define recovery strategies — use mode states with deep history transitions

  5. Assign orthogonals — one per independent concern (navigation, manipulation, monitoring, etc.)

Summary

You learned:

  • How sm_multi_stage_1 uses 5 modes with sequence super states for large-scale missions

  • How sm_cl_px4_mr_test_1 organizes a real flight mission into 6 flight-phase mode states

  • The complete signal wiring chain from state configuration to event-driven transition

  • Cross-orthogonal component access

  • Design principles for multi-stage missions

Further Reading