readyRead signal not activating while using QSerialProt

[Adar70]

Hello. I have this program here:

import sys
from time import sleep

from PySide6 import QtSerialPort as qts
from PySide6 import QtCore as qtc


class Serial_Port():
    def __init__(self):
        self.port = qts.QSerialPort()
        self.port.setBaudRate(qts.QSerialPort.Baud38400)
        
        self.port.readyRead.connect(self.on_receive)
        self.port.errorOccurred.connect(self.on_error)

        qtc.QTimer.singleShot(0, self.program)


    def program(self):
        print(self.con_discon())
        order = [0x86, 0x01]
        for o in order:
            self.send(o.to_bytes())
            sleep(0.001)
        print("fin")

    
    def con_discon(self):
        if self.port.isOpen(): 
            self.port.close() 
            return False
        else: 
            for port in qts.QSerialPortInfo.availablePorts():
                if port.manufacturer() == 'STMicroelectronics' and port.serialNumber() == '0668FF505271754867083433':
                    self.port.setPort(port)
                    break
            return self.port.open(qtc.QIODeviceBase.ReadWrite)


    def send(self, data):
        print("send: ", data)
        self.port.write(data)
    

    def on_receive(self):
        print('!')
        print("message: ", self.port.read(2))


    def on_error(self, error):
        print("Serial port error:")
        print(error.name)
        exit()


def main():
    if not qtc.QCoreApplication.instance(): 
        app = qtc.QCoreApplication(sys.argv) 
    else:
        app = qtc.QCoreApplication.instance() 

    Serial_Port()

    app.exec()


if __name__ == '__main__':
    main()

It's supposed to send 0x86 and then 0x01 through serial port and get an answer from a device. I know the device is working correctly, because the answer is showing up with Termite and, interestingly, when I run this program without an event loop, which looks like this:

import sys
from time import sleep

from PySide6 import QtSerialPort as qts
from PySide6 import QtCore as qtc


class Serial_Port():
    def __init__(self):
        self.port = qts.QSerialPort()
        self.port.setBaudRate(qts.QSerialPort.Baud38400)
        
        self.port.readyRead.connect(self.on_receive)
        self.port.errorOccurred.connect(self.on_error)


    def program(self):
        print(self.con_discon())
        order = [0x86, 0x01]
        for o in order:
            self.send(o.to_bytes())
            sleep(0.001)
        self.port.waitForReadyRead()
        print("fin")

    
    def con_discon(self):
        if self.port.isOpen(): 
            self.port.close() 
            return False
        else: 
            for port in qts.QSerialPortInfo.availablePorts():
                if port.manufacturer() == 'STMicroelectronics' and port.serialNumber() == '0668FF505271754867083433':
                    self.port.setPort(port)
                    break
            return self.port.open(qtc.QIODeviceBase.ReadWrite)


    def send(self, data):
        print("send: ", data)
        self.port.write(data)
    

    def on_receive(self):
        print('!')
        print("message: ", self.port.read(2))


    def on_error(self, error):
        print("Serial port error:")
        print(error.name)
        exit()


def main():
    sp = Serial_Port()
    sp.program()


if __name__ == '__main__':
    main()

I don't know why it doesn't work nor why only without the event loop. With the event loop, after sending the data, it just does nothing. Please help.

[JonB]

@Adar70
Maybe you are doing the above (mostly) in your first code, I looked initially at your second.

Meanwhile, I am worried about your Python lifetime of the instance you create in first code via plain Serial_Port() call. You do not assign return result to any variable. If I am not mistaken, won't the created Serial_Port instance be destroyed immediately after return from Serial_Port.__init__()? Not certain whether the qtc.QTimer.singleShot(0, self.program) will keep it alive. Even if it does, it may die before the reply bytes are received, at least with no waitFor...(). Verify if that is the case, do something to keep the Serial_Port instance around?

[JonB]

@Adar70
Don't do sleep()s. Allow the event loop to run. Don't use both readyRead() signal and waitForReadyRead(). Get rid of the latter. Don't read 2 bytes in case there is only 1. There's a start.

[JonB]

@Adar70
Maybe you are doing the above (mostly) in your first code, I looked initially at your second.

Meanwhile, I am worried about your Python lifetime of the instance you create in first code via plain Serial_Port() call. You do not assign return result to any variable. If I am not mistaken, won't the created Serial_Port instance be destroyed immediately after return from Serial_Port.__init__()? Not certain whether the qtc.QTimer.singleShot(0, self.program) will keep it alive. Even if it does, it may die before the reply bytes are received, at least with no waitFor...(). Verify if that is the case, do something to keep the Serial_Port instance around?

[Adar70]

@JonB Thanks for the reply. After putting the call to Serial_Port() in a variable like sp = Serial_Port() in the code with event loop it worked. Sadly the amount of times the readyRead signal is emitted is unreliable. Sometimes it's two, sometimes it's three. I don't know how to make it more robust. Could you help with that?

[jsulm]

@Adar70 said in readyRead signal not activating while using QSerialProt:

I don't know how to make it more robust

Don't rely on the number of times readyRead is emitted. Instead accumulate the received data until you received all you expect to receive.