Command Structure

EmbMessenger is command based, intended to be used where each command does one simple action. For example, toggle an LED, get the value of an ultrasonic sensor, or set the position for a servo motor. Commands must be defined and registered in two places. On the Device, where the command is implemented; and on the Host, where the command interface is implemented.

Commands

In this example, we'll make three commands.

1. Ping - An empty command, does nothing. Used for testing purposes.
2. Set Led - Set the new state for the LED. Takes one bool parameter, the new LED state.
3. Toggle Led - Toggle the LED. Returns one bool parameter, the new LED state.

Device

bool ledState = false;

// Do nothing, EmbMessenger will just send a message received.
void ping()
{
}

// Set the LED using the parameter from EmbMessenger
void setLed()
{
    // Receive the new LED state
    messenger.read(ledState);
    digitalWrite(LED_BUILTIN, ledState ? HIGH : LOW);
}

// Toggle the LED and return the new state to EmbMessenger
void toggleLed()
{
    ledState = !ledState;
    digitalWrite(LED_BUILTIN, ledState ? HIGH : LOW);

    // Send the new LED state
    messenger.write(ledState);
}

Host

// Doesn't send or receive anything
class Ping : public emb::host::Command
{
};

// Set the new state of the LED
class SetLed : public emb::host::Command
{
    bool m_ledState;

public:
    // Take the new state as a constructor parameter
    SetLed(bool ledState)
    {
        m_ledState = ledState;
    }
    
    // Override the default send method
    void send(emb::host::EmbMessenger* messenger)
    {
        // Send the new LED state
        messenger->write(m_ledState);
    }
};

// Toggle the state of the LED
class ToggleLed : public emb::host::Command
{
    bool m_ledState;

public:
    // Override the default receive method
    void receive(emb::host::EmbMessenger* messenger)
    {
        // Receive the new LED state
        messenger->read(m_ledState);
    }
    
    // Get the new LED state
    bool getLedState() const
    {
        return m_ledState;
    }
};