89 lines
2.2 KiB
Markdown
89 lines
2.2 KiB
Markdown
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Elevator Project
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================
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Example implementation of a simplified elevator logic, using [TinyFSM].
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[TinyFSM]: https://digint.ch/tinyfsm/
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Overview
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--------
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Imagine a elevator having:
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- "Call" button on each floor,
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- "Floor Sensor" on each floor, triggering an event as soon as the
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elevator arrives there,
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- "Alarm" button.
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Implementation
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--------------
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The elevator example implements two state machines interacting with
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each other:
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1. Elevator
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- State: Idle
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- State: Moving
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- State: Panic
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2. Motor
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- State: Stopped
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- State: Up
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- State: Down
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[insert ascii-art here]
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A good state machine design avoids circular dependencies at all
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cost: While the elevator sends events to the motor, the motor NEVER
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sends events to the elevator (top-down only).
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FAQ
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---
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Did you notice the motor starting twice? This is by design, let's
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have a look at the call stack of fsm_list::start() in main.cpp:
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FsmList<Motor, Elevator>::start()
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Motor::set_initial_state()
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Motor::current_state = Stopped
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Elevator::set_initial_state()
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Elevator::current_state = Idle
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Motor::enter()
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Motor:Stopped->entry()
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cout << "Motor: stopped" <-- HERE
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Motor::direction = 0
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Elevator::enter()
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Elevator:Idle->entry()
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send_event(MotorStop)
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Motor::react(MotorStop)
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Motor:Stopped->transit<Stopped>
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Motor:Stopped->exit()
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Motor::current_state = Stopped
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Motor:Stopped->entry()
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cout << "Motor: stopped" <-- HERE
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Motor::direction = 0
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Elevator::react(MotorStop)
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If we really had to work around this, we could either:
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1. Change the initialization (bad design practice!) in main.cpp:
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- fsm_list::start();
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+ fsm_list::set_initial_state();
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+ Elevator::enter();
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2. Modify the Motor:Stopped->entry() function in motor.cpp:
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class Stopped : public Motor {
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void entry() override {
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+ if(direction == 0)
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+ return;
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cout << "Motor: stopped" << endl;
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direction = 0;
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};
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