Serial port buffer Size

[isan]

I open the serial port in ReadWrite mode. First I have to send a command to a device to receive the data.
The packet size sent from the device is 10240 but in serial-> readAll() I only get 4096 bytes
I also use serial-> setReadBufferSize (10240) But nothing changes. Is there a limit to the size of the serial port buffer?

RandomWalk::RandomWalk(RandomWalk::DataHandler *handler, QString port,
                       QString Config, QString model, void *param)
    : stopThread(false), command(false), handler(handler), param(param),
      recievedData{0} {
  serial = new QSerialPort(this);
  connect(serial, &QSerialPort::readyRead, this, &RandomWalk::readData);
  openSerialPort(port, QIODevice::ReadWrite);
  writeData(Config.toUtf8());
}

void RandomWalk::openSerialPort(QString port, QIODevice::OpenModeFlag device) {
  serial->setPortName(port);
  serial->setBaudRate(115200);
  serial->setDataBits(QSerialPort::Data8);
  serial->setParity(QSerialPort::NoParity);
  serial->setStopBits(QSerialPort::OneStop);
  serial->setFlowControl(QSerialPort::NoFlowControl);
  serial->setReadBufferSize(10240);
 // serial->waitForReadyRead(2000);
  if (serial->open(device)) {

    qDebug() << "Connected";

  } else {
    qDebug() << "Open error";
  }
}

void RandomWalk::writeData(const QByteArray &data) { serial->write(data); }

void RandomWalk::readData() {
  while (serial->bytesAvailable()) {
  recievedData.append(serial->readAll());
  }
  qDebug() << "recieveddata" << recievedData.size();

}

[JonB]

@isan
You should not assume there is any relationship between how many bytes readAll() returns and the size of any buffer. readAll()/bytesAvailable() return whatever they currently "see" as there. Repeated calls will later pick up any further data. I do not think you can influence the minimum/maximum number of bytes it returns in any one call.

Since you are (correctly) appending bytes received to a member buffer use that to accumulate whatever you want. If you need to wait for > 4096 bytes for some reason that is the place to do it.

In fact reading QSerialPort::setReadBufferSize() I think you might be better leaving it at the default of 0 which means

If the buffer size is limited to a certain size, QSerialPort will not buffer more than this size of data. The special case of a buffer size of 0 means that the read buffer is unlimited and all incoming data is buffered. This is the default.

So it sounds like specifying a buffer size actually places a maximum bytes limit, risking dropping of data if you do not read it fast enough.

[mrjj]

Hi
Depending on the SENDING hardware, the payload will come in one or more
"waves"/readAll()

So once recievedData.size() is the expected size, all data has been read.

There is no setting to avoid this. Its how it works.