[Interest] Parsing data from serialport

Jérôme Godbout godboutj at amotus.ca
Wed Apr 3 00:01:49 CEST 2019


Make sure your reading loop and processing data are separated. Call you read device when needed or into a loop that can take some pause to avoid 100% CPU usage for nothing.

QByteArray buffer;

void ReadDeviceHaveData()
{

   while(serial_port->bytesAvailable()) // This can be dangerous is data keep coming  and might be removed
{
            // You can read bytes per bytes or smaller chunk over here for better reactivity and less memory consumption
            buffer.append(serial_port->readAll());
            processData();
            serial_port->waitForReadyRead(5);
     }
}

void ProcessData()
{
   int pos = buffer.indexOf(‘\n’);

   while(pos >= 0)
   {
     QByteArray line = buffer.left(pos);
     // Strip trailing \r for windows here
     // Do whatever you need with your line, check data integrity

     // Remove the processed data but leave the unprocessed data alone
     buffer.remove(0, pos + 1); // Remove \n too
     pos = buffer.indexOf(‘\n’);
   }
}

From: Interest <interest-bounces at qt-project.org> On Behalf Of Martin Marmsoler
Sent: April 2, 2019 3:58 PM
To: Thiago Macieira <thiago.macieira at intel.com>
Cc: interest at qt-project.org
Subject: Re: [Interest] Parsing data from serialport

 > To be able to roll back, in case your reading from the device didn't result in
what you wanted or you got an error. See QDataStream.
Ah ok I understand.

So this minimal example
QSerialPort sPort;
sPort.open(QIODevice::ReadOnly);

if(sPort.waitForReadyRead(2000)){

  while (!device.atEnd()) {

        if (device.canReadLine()) {

               newData.push_back(device.readLine());

               linesToRead++;

        } else {

               return;

        }

               }

   ...

}

works fine, if I go trough it step by step (maybe, because enouth data come in). But if I'm to fast it does not work.

If I'm using the signal readyRead I will have the same problem, because new data come everytime. So I check that in the

readyRead function if a complete line come in, and if no complete line I return without doing something otherwise I do

something with the data? Is this the right way?



Martin




Thiago Macieira <thiago.macieira at intel.com<mailto:thiago.macieira at intel.com>> schrieb am Di., 2. Apr. 2019, 18:02:
On Tuesday, 2 April 2019 07:04:03 PDT Martin Marmsoler wrote:
> Thank you Thiago for your response. But what is transactionstart for?

To be able to roll back, in case your reading from the device didn't result in
what you wanted or you got an error. See QDataStream.

--
Thiago Macieira - thiago.macieira (AT) intel.com<http://intel.com>
  Software Architect - Intel System Software Products



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