Reading from Arduino using QSerialPort stops after a few bytes

FlyingDude

Hi,

I am trying to receive bytes from an Arduino's (emulated USB) serial port using QSerialPort.

Currently I simply send an incrementing / overflowing single byte on the arduno side:

void loop() {
static unsigned char cnt = 0;
cnt++;
Serial.write(&cnt, 1);
}

When I connect to the emulated COM-port using putty, I receive an endless stream of bytes, as expected.

However, when I try to achieve the same using QSerialPort, the Arduino sends for a short time (TX led is active), I receive a batch of bytes in one go but then the TX led stays dark and I don't receive any more data.

port.setPortName("COM23");
if (!port.open(QIODevice::ReadWrite)) {
printf("Error opening serial: %d\n", port.error());
}

if(!port.setParity(QSerialPort::NoParity) ||
    !port.setStopBits(QSerialPort::OneStop) ||
    !port.setDataBits(QSerialPort::Data8) ||
    !port.setFlowControl(QSerialPort::NoFlowControl ) ||
    !port.setBaudRate(115200))
 {
    qFatal("Unable to configure serial port");
    exit(1);
 }

char ackStatus = 0;
while(1) {
    int bytesRead = port.read(&ackStatus, 1);

    if(bytesRead > 0) {
      printf("Data received, length: %d, val: %d\n", bytesRead, ackStatus);
      fflush(stdout);
    }else {
      qApp->processEvents(QEventLoop::ExcludeUserInputEvents);
    }
}

Any idea what the difference between putty and QSerialPort might be in this case?

Thank you in advance, Clemens

mrjj

Hi could you try the "Terminal sample"
and see if it has same behavior?

FlyingDude

I figured out, it was nescessary to set DTR:

port.setDataTerminalReady(true);

Thanks & br, Clemens