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How Can I Asynchronously Send a Sequence of Serial Commands and Handle Responses Effectively?
How Can I Asynchronously Send a Sequence of Serial Commands and Handle Responses Effectively?
Dec 26, 2024 am 04:05 AM
Sending a Sequence of Commands and Waiting for Response
Communication over serial ports often requires sending a sequence of commands and waiting for a response after each command. This can be a challenge, especially if the device you're communicating with takes time to process commands. Blocking functions, such as waitForReadyRead(), can stall your program while waiting for a response.
The Problem with Blocking Functions
The issue you encountered is that readLines() returns false when it doesn't find the expected keyword within a certain timeout. This happens when the device sends only a small portion of the response before the timeout expires.
A Non-Blocking Solution
To overcome this problem, you can use a more asynchronous approach implemented with a state machine. A state machine allows you to define different states for your communication protocol and transition between these states based on specific events.
Consider the following state machine:
- Boot State: Sends the "boot" command and waits for a "boot successful" response.
- Send State: Sends the file data to the device.
- Expect State: Waits for a "load successful" response, indicating that the file has been transferred.
You can create a state machine and define these states using Qt's State Machine Framework. The send(), expect(), and delay() functions allow you to send commands, wait for specific responses, and delay transitions.
An Example Implementation
Here's an example implementation of the state machine:
class Programmer : public StatefulObject {
public:
Programmer(QObject *parent = 0) : StatefulObject(parent) {
...
send(&s_boot, &serial, "boot\n");
expect(&s_boot, &serial, "boot successful", &s_send, 1000, &s_failed);
send(&s_send, &serial, ":HULLOTHERE\n:00000001FF\n");
expect(&s_send, &serial, "load successful", &s_ok, 1000, &s_failed);
}
...
};
Benefits of Using a State Machine
Using a state machine provides several benefits:
- Asynchronous: Does not block your program while waiting for a response.
- Configurable: Allows you to define custom states and transitions for your specific communication protocol.
- Extensible: Can be easily extended to handle more complex protocols.
- Thread-safe: Can be implemented in different threads, as communication with the device is handled via signals and slots.
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