QSerialPort reads wrong count of data - c++

Question

here is what I want to do:
I have a measurement device that measures pressure. It's connected via COM1. By sending the "ASCII letter 9" data, respectively measurements are retrieved from this device.
These measurements should be shown in a QTableView-subclass in my GUI. I don't want the GUI to freeze while reading from the measurement device, so I guess this is called non-blocking.
In my code and for testing I want to retrieve 10 measurements in a for-loop. But I always just get 6, sometimes 7.
I have also subclassed QSerialPort.
The code is shown below. A hint what I am doing wrong or maybe even a correction of my code would be very appreciated. Also feel free to comment on the design of the code.
void MainWindow::startInspection()
{
SauterFH_S *sauterFH_S;
try
{
sauterFH_S = new SauterFH_S(new SerialPort(serialPort,
baudRate));
}
catch(QSerialPort::SerialPortError& e)
{
qDebug() << e;
}
connect(sauterFH_S, SIGNAL(measurandAvalaible(char*)),
measurandTableWidget, SLOT(insertMeasurand(char*)));
// Retrieve 10 measurements
for(int i=0; i<10; ++i)
sauterFH_S->getMeasurand();
delete sauterFH_S;
}
The constructor of the subclassed QSerialPort is as follows:
TASte::IO::SerialPort::SerialPort(const QString &portName, qint32
baudRate, DataBits dataBits, Parity parity, StopBits stopBits,
QIODevice::OpenMode openMode, QObject *parent)
:QSerialPort(parent)
{
setPort(QSerialPortInfo(portName));
setBaudRate(baudRate);
setDataBits(dataBits);
setParity(parity);
setStopBits(stopBits);
if( !open(openMode) ) throw error();
}
And here the rest of what should be important:
TASte::Gauge::SauterFH_S::SauterFH_S(IO::SerialPort *port)
:_port(port)
{
connect(_port, SIGNAL(readyRead()),this, SLOT(onReadyRead()));
}
TASte::Gauge::SauterFH_S::~SauterFH_S()
{
// delete _port;
}
void TASte::Gauge::SauterFH_S::getMeasurand()
{
// typedef QByteArray SerialCommand
IO::SerialCommand command("9");
_port->write(command);
}
void TASte::Gauge::SauterFH_S::onReadyRead()
{
// static const int DATA_LENGTH=8;
char data[DATA_LENGTH];
_port->read(data, DATA_LENGTH);
emit measurandAvalaible(data);
}
Thanks in advance!

Answer 1

Object QSerialPort works well if You send and recive data in other thread. In your case data it can be lost, and program sometimes freeze. I had this same problem. I show you something. I write code each using transmition in UDP, but in serialport is this same conception. So first you must create thread for your serial port. In my case I create therad but for UDP. And you must define your all connections each that be some Interafe beetwen Threads MainWindow and SerialPort.
thForUdp = new QThread();
udp->moveToThread(thForUdp);
thForUdp->start();
connect(this , SIGNAL(SIGNAL_RefreshStatus()) , udp , SLOT(SLOT_refreshStatus()) , Qt::QueuedConnection);
connect(udp , SIGNAL(SIGNAL_TransmitionFailed()) , this , SLOT(SLOT_TrasmitionFailed()) , Qt::QueuedConnection); //od
connect(udp , SIGNAL(SIGNAL_ActualStatus(QByteArray)) , schema , SLOT(SLOT_ActualStatus(QByteArray)) , Qt::QueuedConnection);
connect(udp , SIGNAL(SIGNAL_RefreshTimer()) , this , SLOT(SLOT_StartRefreshTimer()) , Qt::QueuedConnection ); //do
connect(this , SIGNAL(SIGNAL_GetAllName()) , udp , SLOT(SLOT_GetAllName()) , Qt::QueuedConnection );
connect(udp , SIGNAL(SIGNAL_AllName(QVector<QString>)) , schema , SLOT(SLOT_AllName(QVector<QString>)), Qt::QueuedConnection);
connect(udp , SIGNAL(SIGNAL_setEnableRefresh(bool)) , this , SLOT(SLOT_setEnableRefresh(bool)) , Qt::QueuedConnection);
Now you must create object inherited from QSerialPort. In my case I inhert from QUdpSocket
class Udp : public QUdpSocket , public Object
{
Q_OBJECT
public:
Udp(Mediator *medium);
private slots:
void SLOT_ReadyToReadStatus();
signals:
void SIGNAL_TransmitionFailed();
void SIGNAL_RefreshTimer();
void SIGNAL_ActualStatus(QByteArray stat);
void SIGNAL_AllName(QVector<QString> vec);
void SIGNAL_setEnableRefresh(bool state);
};
As you see Udp class have all SIGNAL then you see in first block code. Then you creat in your serial port class right signal and slot to send and recever data
In my case this is in construktor Udp
QObject::connect(this , SIGNAL(readyRead()) , this , SLOT(SLOT_ReadyToReadStatus()));`
Now your program will be worked in this rules.
MainWindow form tread A send signal (get data) --->> in object serialport in thread B data is send and in Thread B data is received then serialport send signal to thread A (send recived data to thread A) --->> MainWindow Received data
Very important is communicate between MainWindow and SerialPort via mechanism SIGNAL & SLOT becase the are two difrent thread. This is in QT rule.
This solution will that your program not freeze and data is be complet received, because another thread take care this.
Generaly I recommend use function waitForReadyRead() after you send data, and receive via waitForReadtRead
{
if(!this->waitForReadyRead(3000))
{
// here is wait for data maximum 3 second
// if recived your data find in slot SLOT_ReadyToReadStatus()
}
// if data is correct receive from this block you send to Thread A via SIGNAL!!
QByteArray array
SIGNAL_Here_Data_To_To_Thread_A(array)
}
Try this