How to Send a Sequence of Serial Commands and Handle Responses with Qt's State Machine?

Sending a Sequence of Commands and Waiting for Response

Problem: How to send a sequence of commands to a device connected via serial port and wait for a response, with handling of timeouts and error conditions.

Solution using Qt's State Machine Framework:

Benefits:

• Asynchronous, non-blocking
• Automatic timeout handling
• Clear and readable code structure

Implementation:

1. Create a State Machine:

   • Create a QStateMachine and define states for each step in the communication sequence (e.g., boot, send, expect).

2. Define Action Generators:

   • Define functions that describe actions to be performed when entering each state, such as sending commands or expecting responses.

3. Connect Signals and Transitions:

   • Connect signals (e.g., readyRead) to transition from one state to another.
   • Use GuardedSignalTransition to add conditions to transitions based on received data.

4. Create a Programmer Object:

   • Use StatefulObject as a base class to manage the state machine and signals.
   • Wrap the serial port with AppPipe (a non-blocking QIODevice) and define actions for sending commands and expecting responses.

5. Emulate Device Behavior (Optional):

   • Create another StatefulObject (Device) to simulate the device's responses to commands.

6. In the main function:

   • Instantiate Programmer and Device objects.
   • Connect their AppPipes to allow communication.
   • Start the Programmer object and track its state.
   • Optionally start the Device object and track its state.

Example Code:

// Programmer object using Qt's State Machine Framework
class Programmer : public StatefulObject {
  Q_OBJECT
  AppPipe m_port;
  QStateMachine m_mach;
  State s_boot, s_send;
public:
  Programmer() : StatefulObject() {
    connectSignals();
    m_mach.setInitialState(&s_boot);
    send(&s_boot, &m_port, "boot\n");
    expect(&s_boot, &m_port, "boot successful", &s_send, 1000, &s_failed);
    ... // Define other states and actions
  }
  void start() { m_mach.start(); }
};

// main function
int main() {
  QApplication app;
  Programmer prog;
  Device dev;
  dev.pipe().addOther(&prog.pipe());

  prog.pipe().addHasOutgoing([](const QByteArray &data){ qDebug() << "> " << data; });
  prog.pipe().addHasIncoming([](const QByteArray &data){ qDebug() << "< " << data; });

  prog.start();
  return app.exec();
}

Advantages:

• Clean and structured code, minimizing the risk of race conditions or missed responses.
• Possibility to add complex state transitions and error handling scenarios.
• Extensibility to support various communication protocols with different command sequences.

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